A modern list API for Emacs. No
'cl
required.
It's available on GNU ELPA and MELPA:
M-x package-install dash
Or you can just dump dash.el
in your load-path
somewhere.
If you want the function combinators, then also:
M-x package-install dash-functional
Add something like this to the library's headers:
;; Package-Requires: ((dash "2.17.0"))
To get function combinators:
;; Package-Requires: ((dash "2.17.0") (dash-functional "1.2.0"))
-
For backward compatibility reasons,
-zip
when called with two lists returns a list of cons cells, rather than a list of proper lists. This is a clunky API, and may be changed in a future release to always return a list of proper lists, as-zip-lists
currently does.N.B.: Do not rely on the current behavior of
-zip
for two lists. Instead, use-zip-pair
for a list of cons cells, and-zip-lists
for a list of proper lists.
Font lock of special Dash variables (it
, acc
, etc.) in Emacs Lisp
buffers can optionally be enabled with the autoloaded minor mode
dash-fontify-mode
. In older Emacs versions which do not dynamically
detect macros, the minor mode also fontifies Dash macro calls.
To automatically enable the minor mode in all Emacs Lisp buffers, just
call its autoloaded global counterpart global-dash-fontify-mode
,
either interactively or from your user-init-file
:
(global-dash-fontify-mode)
While editing Elisp files, you can use C-h S
(info-lookup-symbol
)
to look up Elisp symbols in the relevant Info manuals (see (emacs) Info Lookup
).
To enable the same for Dash symbols, use the command
dash-register-info-lookup
. It can be called directly when needed,
or automatically from your user-init-file
. For example:
(with-eval-after-load 'info-look
(dash-register-info-lookup))
All functions and constructs in the library use a dash (-
) prefix.
The library also provides anaphoric macro versions of functions where
that makes sense. The names of these macros are prefixed with two
dashes (--
) instead of one.
While -map
applies a function to each element of a list, its
anaphoric counterpart --map
evaluates a form with the local variable
it
temporarily bound to the current list element instead. For
example:
(-map (lambda (n) (* n n)) '(1 2 3 4)) ; Normal version.
(--map (* it it) '(1 2 3 4)) ; Anaphoric version.
The normal version can of course also be written as follows:
(defun my-square (n)
"Return N multiplied by itself."
(* n n))
(-map #'my-square '(1 2 3 4))
This demonstrates the utility of both versions.
Functions in this category take a transforming function, which is then applied sequentially to each or selected elements of the input list. The results are collected in order and returned as a new list.
- -map
(fn list)
- -map-when
(pred rep list)
- -map-first
(pred rep list)
- -map-last
(pred rep list)
- -map-indexed
(fn list)
- -annotate
(fn list)
- -splice
(pred fun list)
- -splice-list
(pred new-list list)
- -mapcat
(fn list)
- -copy
(list)
Functions returning a sublist of the original list.
- -filter
(pred list)
- -remove
(pred list)
- -remove-first
(pred list)
- -remove-last
(pred list)
- -remove-item
(item list)
- -non-nil
(list)
- -slice
(list from &optional to step)
- -take
(n list)
- -take-last
(n list)
- -drop
(n list)
- -drop-last
(n list)
- -take-while
(pred list)
- -drop-while
(pred list)
- -select-by-indices
(indices list)
- -select-columns
(columns table)
- -select-column
(column table)
Functions returning a modified copy of the input list.
- -keep
(fn list)
- -concat
(&rest lists)
- -flatten
(l)
- -flatten-n
(num list)
- -replace
(old new list)
- -replace-first
(old new list)
- -replace-last
(old new list)
- -insert-at
(n x list)
- -replace-at
(n x list)
- -update-at
(n func list)
- -remove-at
(n list)
- -remove-at-indices
(indices list)
Functions reducing lists to a single value (which may also be a list).
- -reduce-from
(fn init list)
- -reduce-r-from
(fn init list)
- -reduce
(fn list)
- -reduce-r
(fn list)
- -reductions-from
(fn init list)
- -reductions-r-from
(fn init list)
- -reductions
(fn list)
- -reductions-r
(fn list)
- -count
(pred list)
- -sum
(list)
- -running-sum
(list)
- -product
(list)
- -running-product
(list)
- -inits
(list)
- -tails
(list)
- -common-prefix
(&rest lists)
- -common-suffix
(&rest lists)
- -min
(list)
- -min-by
(comparator list)
- -max
(list)
- -max-by
(comparator list)
Operations dual to reductions, building lists from a seed value rather than consuming a list to produce a single value.
- -any?
(pred list)
- -all?
(pred list)
- -none?
(pred list)
- -only-some?
(pred list)
- -contains?
(list element)
- -same-items?
(list list2)
- -is-prefix?
(prefix list)
- -is-suffix?
(suffix list)
- -is-infix?
(infix list)
- -cons-pair?
(obj)
Functions partitioning the input list into a list of lists.
- -split-at
(n list)
- -split-with
(pred list)
- -split-on
(item list)
- -split-when
(fn list)
- -separate
(pred list)
- -partition
(n list)
- -partition-all
(n list)
- -partition-in-steps
(n step list)
- -partition-all-in-steps
(n step list)
- -partition-by
(fn list)
- -partition-by-header
(fn list)
- -partition-after-pred
(pred list)
- -partition-before-pred
(pred list)
- -partition-before-item
(item list)
- -partition-after-item
(item list)
- -group-by
(fn list)
Return indices of elements based on predicates, sort elements by indices etc.
- -elem-index
(elem list)
- -elem-indices
(elem list)
- -find-index
(pred list)
- -find-last-index
(pred list)
- -find-indices
(pred list)
- -grade-up
(comparator list)
- -grade-down
(comparator list)
Operations pretending lists are sets.
- -union
(list list2)
- -difference
(list list2)
- -intersection
(list list2)
- -powerset
(list)
- -permutations
(list)
- -distinct
(list)
Other list functions not fit to be classified elsewhere.
- -rotate
(n list)
- -repeat
(n x)
- -cons*
(&rest args)
- -snoc
(list elem &rest elements)
- -interpose
(sep list)
- -interleave
(&rest lists)
- -iota
(count &optional start step)
- -zip-with
(fn list1 list2)
- -zip
(&rest lists)
- -zip-lists
(&rest lists)
- -zip-fill
(fill-value &rest lists)
- -unzip
(lists)
- -cycle
(list)
- -pad
(fill-value &rest lists)
- -table
(fn &rest lists)
- -table-flat
(fn &rest lists)
- -first
(pred list)
- -some
(pred list)
- -last
(pred list)
- -first-item
(list)
- -second-item
(list)
- -third-item
(list)
- -fourth-item
(list)
- -fifth-item
(list)
- -last-item
(list)
- -butlast
(list)
- -sort
(comparator list)
- -list
(arg)
- -fix
(fn list)
Functions pretending lists are trees.
- -tree-seq
(branch children tree)
- -tree-map
(fn tree)
- -tree-map-nodes
(pred fun tree)
- -tree-reduce
(fn tree)
- -tree-reduce-from
(fn init-value tree)
- -tree-mapreduce
(fn folder tree)
- -tree-mapreduce-from
(fn folder init-value tree)
- -clone
(list)
- ->
(x &optional form &rest more)
- ->>
(x &optional form &rest more)
- -->
(x &rest forms)
- -as->
(value variable &rest forms)
- -some->
(x &optional form &rest more)
- -some->>
(x &optional form &rest more)
- -some-->
(expr &rest forms)
- -doto
(init &rest forms)
Convenient versions of let
and let*
constructs combined with flow control.
- -when-let
((var val) &rest body)
- -when-let*
(vars-vals &rest body)
- -if-let
((var val) then &rest else)
- -if-let*
(vars-vals then &rest else)
- -let
(varlist &rest body)
- -let*
(varlist &rest body)
- -lambda
(match-form &rest body)
- -setq
([match-form val] ...)
Functions iterating over lists for side effect only.
- -each
(list fn)
- -each-while
(list pred fn)
- -each-indexed
(list fn)
- -each-r
(list fn)
- -each-r-while
(list pred fn)
- -dotimes
(num fn)
These combinators require Emacs 24 for its lexical scope. So they are offered in a separate package: dash-functional
.
- -partial
(fn &rest args)
- -rpartial
(fn &rest args)
- -juxt
(&rest fns)
- -compose
(&rest fns)
- -applify
(fn)
- -on
(operator transformer)
- -flip
(func)
- -const
(c)
- -cut
(&rest params)
- -not
(pred)
- -orfn
(&rest preds)
- -andfn
(&rest preds)
- -iteratefn
(fn n)
- -fixfn
(fn &optional equal-test halt-test)
- -prodfn
(&rest fns)
Functions in this category take a transforming function, which is then applied sequentially to each or selected elements of the input list. The results are collected in order and returned as a new list.
Apply fn
to each item in list
and return the list of results.
This function's anaphoric counterpart is --map
.
(-map (lambda (num) (* num num)) '(1 2 3 4)) ;; => '(1 4 9 16)
(-map #'1+ '(1 2 3 4)) ;; => '(2 3 4 5)
(--map (* it it) '(1 2 3 4)) ;; => '(1 4 9 16)
Return a new list where the elements in list
that do not match the pred
function
are unchanged, and where the elements in list
that do match the pred
function are mapped
through the rep
function.
Alias: -replace-where
See also: -update-at
(-map-when 'even? 'square '(1 2 3 4)) ;; => '(1 4 3 16)
(--map-when (> it 2) (* it it) '(1 2 3 4)) ;; => '(1 2 9 16)
(--map-when (= it 2) 17 '(1 2 3 4)) ;; => '(1 17 3 4)
Replace first item in list
satisfying pred
with result of rep
called on this item.
See also: -map-when
, -replace-first
(-map-first 'even? 'square '(1 2 3 4)) ;; => '(1 4 3 4)
(--map-first (> it 2) (* it it) '(1 2 3 4)) ;; => '(1 2 9 4)
(--map-first (= it 2) 17 '(1 2 3 2)) ;; => '(1 17 3 2)
Replace last item in list
satisfying pred
with result of rep
called on this item.
See also: -map-when
, -replace-last
(-map-last 'even? 'square '(1 2 3 4)) ;; => '(1 2 3 16)
(--map-last (> it 2) (* it it) '(1 2 3 4)) ;; => '(1 2 3 16)
(--map-last (= it 2) 17 '(1 2 3 2)) ;; => '(1 2 3 17)
Apply fn
to each index and item in list
and return the list of results.
This is like -map
, but fn
takes two arguments: the index of the
current element within list
, and the element itself.
This function's anaphoric counterpart is --map-indexed
.
For a side-effecting variant, see also -each-indexed
.
(-map-indexed (lambda (index item) (- item index)) '(1 2 3 4)) ;; => '(1 1 1 1)
(--map-indexed (- it it-index) '(1 2 3 4)) ;; => '(1 1 1 1)
(-map-indexed #'* '(1 2 3 4)) ;; => '(0 2 6 12)
Return a list of cons cells where each cell is fn
applied to each
element of list
paired with the unmodified element of list
.
(-annotate '1+ '(1 2 3)) ;; => '((2 . 1) (3 . 2) (4 . 3))
(-annotate 'length '(("h" "e" "l" "l" "o") ("hello" "world"))) ;; => '((5 "h" "e" "l" "l" "o") (2 "hello" "world"))
(--annotate (< 1 it) '(0 1 2 3)) ;; => '((nil . 0) (nil . 1) (t . 2) (t . 3))
Splice lists generated by fun
in place of elements matching pred
in list
.
fun
takes the element matching pred
as input.
This function can be used as replacement for ,@
in case you
need to splice several lists at marked positions (for example
with keywords).
See also: -splice-list
, -insert-at
(-splice 'even? (lambda (x) (list x x)) '(1 2 3 4)) ;; => '(1 2 2 3 4 4)
(--splice 't (list it it) '(1 2 3 4)) ;; => '(1 1 2 2 3 3 4 4)
(--splice (equal it :magic) '((list of) (magical) (code)) '((foo) (bar) :magic (baz))) ;; => '((foo) (bar) (list of) (magical) (code) (baz))
Splice new-list
in place of elements matching pred
in list
.
See also: -splice
, -insert-at
(-splice-list 'keywordp '(a b c) '(1 :foo 2)) ;; => '(1 a b c 2)
(-splice-list 'keywordp nil '(1 :foo 2)) ;; => '(1 2)
(--splice-list (keywordp it) '(a b c) '(1 :foo 2)) ;; => '(1 a b c 2)
Return the concatenation of the result of mapping fn
over list
.
Thus function fn
should return a list.
(-mapcat 'list '(1 2 3)) ;; => '(1 2 3)
(-mapcat (lambda (item) (list 0 item)) '(1 2 3)) ;; => '(0 1 0 2 0 3)
(--mapcat (list 0 it) '(1 2 3)) ;; => '(0 1 0 2 0 3)
Create a shallow copy of list
.
(-copy '(1 2 3)) ;; => '(1 2 3)
(let ((a '(1 2 3))) (eq a (-copy a))) ;; => nil
Functions returning a sublist of the original list.
Return a new list of the items in list
for which pred
returns non-nil.
Alias: -select
.
This function's anaphoric counterpart is --filter
.
For similar operations, see also -keep
and -remove
.
(-filter (lambda (num) (= 0 (% num 2))) '(1 2 3 4)) ;; => '(2 4)
(-filter #'natnump '(-2 -1 0 1 2)) ;; => '(0 1 2)
(--filter (= 0 (% it 2)) '(1 2 3 4)) ;; => '(2 4)
Return a new list of the items in list
for which pred
returns nil.
Alias: -reject
.
This function's anaphoric counterpart is --remove
.
For similar operations, see also -keep
and -filter
.
(-remove (lambda (num) (= 0 (% num 2))) '(1 2 3 4)) ;; => '(1 3)
(-remove #'natnump '(-2 -1 0 1 2)) ;; => '(-2 -1)
(--remove (= 0 (% it 2)) '(1 2 3 4)) ;; => '(1 3)
Remove the first item from list
for which pred
returns non-nil.
This is a non-destructive operation, but only the front of list
leading up to the removed item is a copy; the rest is list
's
original tail. If no item is removed, then the result is a
complete copy.
Alias: -reject-first
.
This function's anaphoric counterpart is --remove-first
.
See also -map-first
, -remove-item
, and -remove-last
.
(-remove-first #'natnump '(-2 -1 0 1 2)) ;; => '(-2 -1 1 2)
(-remove-first #'stringp '(1 2 "first" "second")) ;; => '(1 2 "second")
(--remove-first (> it 3) '(1 2 3 4 5 6)) ;; => '(1 2 3 5 6)
Remove the last item from list
for which pred
returns non-nil.
The result is a copy of list
regardless of whether an element is
removed.
Alias: -reject-last
.
This function's anaphoric counterpart is --remove-last
.
See also -map-last
, -remove-item
, and -remove-first
.
(-remove-last #'natnump '(1 3 5 4 7 8 10 -11)) ;; => '(1 3 5 4 7 8 -11)
(-remove-last #'stringp '(1 2 "last" "second")) ;; => '(1 2 "last")
(--remove-last (> it 3) '(1 2 3 4 5 6 7 8 9 10)) ;; => '(1 2 3 4 5 6 7 8 9)
Return a copy of list
with all occurrences of item
removed.
The comparison is done with equal
.
(-remove-item 3 '(1 2 3 2 3 4 5 3)) ;; => '(1 2 2 4 5)
(-remove-item 'foo '(foo bar baz foo)) ;; => '(bar baz)
(-remove-item "bob" '("alice" "bob" "eve" "bob")) ;; => '("alice" "eve")
Return a copy of list
with all nil items removed.
(-non-nil '(nil 1 nil 2 nil nil 3 4 nil 5 nil)) ;; => '(1 2 3 4 5)
(-non-nil '((nil))) ;; => '((nil))
(-non-nil '()) ;; => '()
Return copy of list
, starting from index from
to index to
.
from
or to
may be negative. These values are then interpreted
modulo the length of the list.
If step
is a number, only each step
th item in the resulting
section is returned. Defaults to 1.
(-slice '(1 2 3 4 5) 1) ;; => '(2 3 4 5)
(-slice '(1 2 3 4 5) 0 3) ;; => '(1 2 3)
(-slice '(1 2 3 4 5 6 7 8 9) 1 -1 2) ;; => '(2 4 6 8)
Return a copy of the first n
items in list
.
Return a copy of list
if it contains n
items or fewer.
Return nil if n
is zero or less.
See also: -take-last
.
(-take 3 '(1 2 3 4 5)) ;; => '(1 2 3)
(-take 17 '(1 2 3 4 5)) ;; => '(1 2 3 4 5)
(-take 0 '(1 2 3 4 5)) ;; => nil
Return a copy of the last n
items of list
in order.
Return a copy of list
if it contains n
items or fewer.
Return nil if n
is zero or less.
See also: -take
.
(-take-last 3 '(1 2 3 4 5)) ;; => '(3 4 5)
(-take-last 17 '(1 2 3 4 5)) ;; => '(1 2 3 4 5)
(-take-last 1 '(1 2 3 4 5)) ;; => '(5)
Return the tail (not a copy) of list
without the first n
items.
Return nil if list
contains n
items or fewer.
Return list
if n
is zero or less.
For another variant, see also -drop-last
.
(-drop 3 '(1 2 3 4 5)) ;; => '(4 5)
(-drop 17 '(1 2 3 4 5)) ;; => nil
(-drop 0 '(1 2 3 4 5)) ;; => '(1 2 3 4 5)
Return a copy of list
without its last n
items.
Return a copy of list
if n
is zero or less.
Return nil if list
contains n
items or fewer.
See also: -drop
.
(-drop-last 3 '(1 2 3 4 5)) ;; => '(1 2)
(-drop-last 17 '(1 2 3 4 5)) ;; => nil
(-drop-last 0 '(1 2 3 4 5)) ;; => '(1 2 3 4 5)
Take successive items from list
for which pred
returns non-nil.
pred
is a function of one argument. Return a new list of the
successive elements from the start of list
for which pred
returns
non-nil.
This function's anaphoric counterpart is --take-while
.
For another variant, see also -drop-while
.
(-take-while #'even? '(1 2 3 4)) ;; => nil
(-take-while #'even? '(2 4 5 6)) ;; => '(2 4)
(--take-while (< it 4) '(1 2 3 4 3 2 1)) ;; => '(1 2 3)
Drop successive items from list
for which pred
returns non-nil.
pred
is a function of one argument. Return the tail (not a copy)
of list
starting from its first element for which pred
returns
nil.
This function's anaphoric counterpart is --drop-while
.
For another variant, see also -take-while
.
(-drop-while #'even? '(1 2 3 4)) ;; => '(1 2 3 4)
(-drop-while #'even? '(2 4 5 6)) ;; => '(5 6)
(--drop-while (< it 4) '(1 2 3 4 3 2 1)) ;; => '(4 3 2 1)
Return a list whose elements are elements from list
selected
as (nth i list)
for all i from indices
.
(-select-by-indices '(4 10 2 3 6) '("v" "e" "l" "o" "c" "i" "r" "a" "p" "t" "o" "r")) ;; => '("c" "o" "l" "o" "r")
(-select-by-indices '(2 1 0) '("a" "b" "c")) ;; => '("c" "b" "a")
(-select-by-indices '(0 1 2 0 1 3 3 1) '("f" "a" "r" "l")) ;; => '("f" "a" "r" "f" "a" "l" "l" "a")
Select columns
from table
.
table
is a list of lists where each element represents one row.
It is assumed each row has the same length.
Each row is transformed such that only the specified columns
are
selected.
See also: -select-column
, -select-by-indices
(-select-columns '(0 2) '((1 2 3) (a b c) (:a :b :c))) ;; => '((1 3) (a c) (:a :c))
(-select-columns '(1) '((1 2 3) (a b c) (:a :b :c))) ;; => '((2) (b) (:b))
(-select-columns nil '((1 2 3) (a b c) (:a :b :c))) ;; => '(nil nil nil)
Select column
from table
.
table
is a list of lists where each element represents one row.
It is assumed each row has the same length.
The single selected column is returned as a list.
See also: -select-columns
, -select-by-indices
(-select-column 1 '((1 2 3) (a b c) (:a :b :c))) ;; => '(2 b :b)
Functions returning a modified copy of the input list.
Return a new list of the non-nil results of applying fn
to each item in list
.
Like -filter
, but returns the non-nil results of fn
instead of
the corresponding elements of list
.
Its anaphoric counterpart is --keep
.
(-keep #'cdr '((1 2 3) (4 5) (6))) ;; => '((2 3) (5))
(-keep (lambda (n) (and (> n 3) (* 10 n))) '(1 2 3 4 5 6)) ;; => '(40 50 60)
(--keep (and (> it 3) (* 10 it)) '(1 2 3 4 5 6)) ;; => '(40 50 60)
Return a new list with the concatenation of the elements in the supplied lists
.
(-concat '(1)) ;; => '(1)
(-concat '(1) '(2)) ;; => '(1 2)
(-concat '(1) '(2 3) '(4)) ;; => '(1 2 3 4)
Take a nested list l
and return its contents as a single, flat list.
Note that because nil
represents a list of zero elements (an
empty list), any mention of nil in l
will disappear after
flattening. If you need to preserve nils, consider -flatten-n
or map them to some unique symbol and then map them back.
Conses of two atoms are considered "terminals", that is, they aren't flattened further.
See also: -flatten-n
(-flatten '((1))) ;; => '(1)
(-flatten '((1 (2 3) (((4 (5))))))) ;; => '(1 2 3 4 5)
(-flatten '(1 2 (3 . 4))) ;; => '(1 2 (3 . 4))
Flatten num
levels of a nested list
.
See also: -flatten
(-flatten-n 1 '((1 2) ((3 4) ((5 6))))) ;; => '(1 2 (3 4) ((5 6)))
(-flatten-n 2 '((1 2) ((3 4) ((5 6))))) ;; => '(1 2 3 4 (5 6))
(-flatten-n 3 '((1 2) ((3 4) ((5 6))))) ;; => '(1 2 3 4 5 6)
Replace all old
items in list
with new
.
Elements are compared using equal
.
See also: -replace-at
(-replace 1 "1" '(1 2 3 4 3 2 1)) ;; => '("1" 2 3 4 3 2 "1")
(-replace "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo")) ;; => '("a" "nice" "bar" "sentence" "about" "bar")
(-replace 1 2 nil) ;; => nil
Replace the first occurrence of old
with new
in list
.
Elements are compared using equal
.
See also: -map-first
(-replace-first 1 "1" '(1 2 3 4 3 2 1)) ;; => '("1" 2 3 4 3 2 1)
(-replace-first "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo")) ;; => '("a" "nice" "bar" "sentence" "about" "foo")
(-replace-first 1 2 nil) ;; => nil
Replace the last occurrence of old
with new
in list
.
Elements are compared using equal
.
See also: -map-last
(-replace-last 1 "1" '(1 2 3 4 3 2 1)) ;; => '(1 2 3 4 3 2 "1")
(-replace-last "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo")) ;; => '("a" "nice" "foo" "sentence" "about" "bar")
(-replace-last 1 2 nil) ;; => nil
Return a list with x
inserted into list
at position n
.
See also: -splice
, -splice-list
(-insert-at 1 'x '(a b c)) ;; => '(a x b c)
(-insert-at 12 'x '(a b c)) ;; => '(a b c x)
Return a list with element at n
th position in list
replaced with x
.
See also: -replace
(-replace-at 0 9 '(0 1 2 3 4 5)) ;; => '(9 1 2 3 4 5)
(-replace-at 1 9 '(0 1 2 3 4 5)) ;; => '(0 9 2 3 4 5)
(-replace-at 4 9 '(0 1 2 3 4 5)) ;; => '(0 1 2 3 9 5)
Return a list with element at n
th position in list
replaced with (func (nth n list))
.
See also: -map-when
(-update-at 0 (lambda (x) (+ x 9)) '(0 1 2 3 4 5)) ;; => '(9 1 2 3 4 5)
(-update-at 1 (lambda (x) (+ x 8)) '(0 1 2 3 4 5)) ;; => '(0 9 2 3 4 5)
(--update-at 2 (length it) '("foo" "bar" "baz" "quux")) ;; => '("foo" "bar" 3 "quux")
Return a list with element at n
th position in list
removed.
See also: -remove-at-indices
, -remove
(-remove-at 0 '("0" "1" "2" "3" "4" "5")) ;; => '("1" "2" "3" "4" "5")
(-remove-at 1 '("0" "1" "2" "3" "4" "5")) ;; => '("0" "2" "3" "4" "5")
(-remove-at 2 '("0" "1" "2" "3" "4" "5")) ;; => '("0" "1" "3" "4" "5")
Return a list whose elements are elements from list
without
elements selected as (nth i list)
for all i
from indices
.
See also: -remove-at
, -remove
(-remove-at-indices '(0) '("0" "1" "2" "3" "4" "5")) ;; => '("1" "2" "3" "4" "5")
(-remove-at-indices '(0 2 4) '("0" "1" "2" "3" "4" "5")) ;; => '("1" "3" "5")
(-remove-at-indices '(0 5) '("0" "1" "2" "3" "4" "5")) ;; => '("1" "2" "3" "4")
Functions reducing lists to a single value (which may also be a list).
Reduce the function fn
across list
, starting with init
.
Return the result of applying fn
to init
and the first element of
list
, then applying fn
to that result and the second element,
etc. If list
is empty, return init
without calling fn
.
This function's anaphoric counterpart is --reduce-from
.
For other folds, see also -reduce
and -reduce-r
.
(-reduce-from #'- 10 '(1 2 3)) ;; => 4
(-reduce-from #'list 10 '(1 2 3)) ;; => '(((10 1) 2) 3)
(--reduce-from (concat acc " " it) "START" '("a" "b" "c")) ;; => "START a b c"
Reduce the function fn
across list
in reverse, starting with init
.
Return the result of applying fn
to the last element of list
and
init
, then applying fn
to the second-to-last element and the
previous result of fn
, etc. That is, the first argument of fn
is
the current element, and its second argument the accumulated
value. If list
is empty, return init
without calling fn
.
This function is like -reduce-from
but the operation associates
from the right rather than left. In other words, it starts from
the end of list
and flips the arguments to fn
. Conceptually, it
is like replacing the conses in list
with applications of fn
, and
its last link with init
, and evaluating the resulting expression.
This function's anaphoric counterpart is --reduce-r-from
.
For other folds, see also -reduce-r
and -reduce
.
(-reduce-r-from #'- 10 '(1 2 3)) ;; => -8
(-reduce-r-from #'list 10 '(1 2 3)) ;; => '(1 (2 (3 10)))
(--reduce-r-from (concat it " " acc) "END" '("a" "b" "c")) ;; => "a b c END"
Reduce the function fn
across list
.
Return the result of applying fn
to the first two elements of
list
, then applying fn
to that result and the third element, etc.
If list
contains a single element, return it without calling fn
.
If list
is empty, return the result of calling fn
with no
arguments.
This function's anaphoric counterpart is --reduce
.
For other folds, see also -reduce-from
and -reduce-r
.
(-reduce #'- '(1 2 3 4)) ;; => -8
(-reduce #'list '(1 2 3 4)) ;; => '(((1 2) 3) 4)
(--reduce (format "%s-%d" acc it) '(1 2 3)) ;; => "1-2-3"
Reduce the function fn
across list
in reverse.
Return the result of applying fn
to the last two elements of
list
, then applying fn
to the third-to-last element and the
previous result of fn
, etc. That is, the first argument of fn
is
the current element, and its second argument the accumulated
value. If list
contains a single element, return it without
calling fn
. If list
is empty, return the result of calling fn
with no arguments.
This function is like -reduce
but the operation associates from
the right rather than left. In other words, it starts from the
end of list
and flips the arguments to fn
. Conceptually, it is
like replacing the conses in list
with applications of fn
,
ignoring its last link, and evaluating the resulting expression.
This function's anaphoric counterpart is --reduce-r
.
For other folds, see also -reduce-r-from
and -reduce
.
(-reduce-r #'- '(1 2 3 4)) ;; => -2
(-reduce-r #'list '(1 2 3 4)) ;; => '(1 (2 (3 4)))
(--reduce-r (format "%s-%d" acc it) '(1 2 3)) ;; => "3-2-1"
Return a list of fn
's intermediate reductions across list
.
That is, a list of the intermediate values of the accumulator
when -reduce-from
(which see) is called with the same
arguments.
This function's anaphoric counterpart is --reductions-from
.
For other folds, see also -reductions
and -reductions-r
.
(-reductions-from #'max 0 '(2 1 4 3)) ;; => '(0 2 2 4 4)
(-reductions-from #'* 1 '(1 2 3 4)) ;; => '(1 1 2 6 24)
(--reductions-from (format "(FN %s %d)" acc it) "INIT" '(1 2 3)) ;; => '("INIT" "(FN INIT 1)" "(FN (FN INIT 1) 2)" "(FN (FN (FN INIT 1) 2) 3)")
Return a list of fn
's intermediate reductions across reversed list
.
That is, a list of the intermediate values of the accumulator
when -reduce-r-from
(which see) is called with the same
arguments.
This function's anaphoric counterpart is --reductions-r-from
.
For other folds, see also -reductions
and -reductions-r
.
(-reductions-r-from #'max 0 '(2 1 4 3)) ;; => '(4 4 4 3 0)
(-reductions-r-from #'* 1 '(1 2 3 4)) ;; => '(24 24 12 4 1)
(--reductions-r-from (format "(FN %d %s)" it acc) "INIT" '(1 2 3)) ;; => '("(FN 1 (FN 2 (FN 3 INIT)))" "(FN 2 (FN 3 INIT))" "(FN 3 INIT)" "INIT")
Return a list of fn
's intermediate reductions across list
.
That is, a list of the intermediate values of the accumulator
when -reduce
(which see) is called with the same arguments.
This function's anaphoric counterpart is --reductions
.
For other folds, see also -reductions
and -reductions-r
.
(-reductions #'+ '(1 2 3 4)) ;; => '(1 3 6 10)
(-reductions #'* '(1 2 3 4)) ;; => '(1 2 6 24)
(--reductions (format "(FN %s %d)" acc it) '(1 2 3)) ;; => '(1 "(FN 1 2)" "(FN (FN 1 2) 3)")
Return a list of fn
's intermediate reductions across reversed list
.
That is, a list of the intermediate values of the accumulator
when -reduce-r
(which see) is called with the same arguments.
This function's anaphoric counterpart is --reductions-r
.
For other folds, see also -reductions-r-from
and
-reductions
.
(-reductions-r #'+ '(1 2 3 4)) ;; => '(10 9 7 4)
(-reductions-r #'* '(1 2 3 4)) ;; => '(24 24 12 4)
(--reductions-r (format "(FN %d %s)" it acc) '(1 2 3)) ;; => '("(FN 1 (FN 2 3))" "(FN 2 3)" 3)
Counts the number of items in list
where (pred
item) is non-nil.
(-count 'even? '(1 2 3 4 5)) ;; => 2
(--count (< it 4) '(1 2 3 4)) ;; => 3
Return the sum of list
.
(-sum '()) ;; => 0
(-sum '(1)) ;; => 1
(-sum '(1 2 3 4)) ;; => 10
Return a list with running sums of items in list
.
list
must be non-empty.
(-running-sum '(1 2 3 4)) ;; => '(1 3 6 10)
(-running-sum '(1)) ;; => '(1)
(-running-sum nil) ;; Error
Return the product of list
.
(-product '()) ;; => 1
(-product '(1)) ;; => 1
(-product '(1 2 3 4)) ;; => 24
Return a list with running products of items in list
.
list
must be non-empty.
(-running-product '(1 2 3 4)) ;; => '(1 2 6 24)
(-running-product '(1)) ;; => '(1)
(-running-product nil) ;; Error
Return all prefixes of list
.
(-inits '(1 2 3 4)) ;; => '(nil (1) (1 2) (1 2 3) (1 2 3 4))
(-inits nil) ;; => '(nil)
(-inits '(1)) ;; => '(nil (1))
Return all suffixes of list
(-tails '(1 2 3 4)) ;; => '((1 2 3 4) (2 3 4) (3 4) (4) nil)
(-tails nil) ;; => '(nil)
(-tails '(1)) ;; => '((1) nil)
Return the longest common prefix of lists
.
(-common-prefix '(1)) ;; => '(1)
(-common-prefix '(1 2) '(3 4) '(1 2)) ;; => nil
(-common-prefix '(1 2) '(1 2 3) '(1 2 3 4)) ;; => '(1 2)
Return the longest common suffix of lists
.
(-common-suffix '(1)) ;; => '(1)
(-common-suffix '(1 2) '(3 4) '(1 2)) ;; => nil
(-common-suffix '(1 2 3 4) '(2 3 4) '(3 4)) ;; => '(3 4)
Return the smallest value from list
of numbers or markers.
(-min '(0)) ;; => 0
(-min '(3 2 1)) ;; => 1
(-min '(1 2 3)) ;; => 1
Take a comparison function comparator
and a list
and return
the least element of the list by the comparison function.
See also combinator -on
which can transform the values before
comparing them.
(-min-by '> '(4 3 6 1)) ;; => 1
(--min-by (> (car it) (car other)) '((1 2 3) (2) (3 2))) ;; => '(1 2 3)
(--min-by (> (length it) (length other)) '((1 2 3) (2) (3 2))) ;; => '(2)
Return the largest value from list
of numbers or markers.
(-max '(0)) ;; => 0
(-max '(3 2 1)) ;; => 3
(-max '(1 2 3)) ;; => 3
Take a comparison function comparator
and a list
and return
the greatest element of the list by the comparison function.
See also combinator -on
which can transform the values before
comparing them.
(-max-by '> '(4 3 6 1)) ;; => 6
(--max-by (> (car it) (car other)) '((1 2 3) (2) (3 2))) ;; => '(3 2)
(--max-by (> (length it) (length other)) '((1 2 3) (2) (3 2))) ;; => '(1 2 3)
Operations dual to reductions, building lists from a seed value rather than consuming a list to produce a single value.
Return a list of iterated applications of fun
to init
.
This means a list of the form:
(`init` (`fun` `init`) (`fun` (`fun` `init`)) ...)
n
is the length of the returned list.
(-iterate #'1+ 1 10) ;; => '(1 2 3 4 5 6 7 8 9 10)
(-iterate (lambda (x) (+ x x)) 2 5) ;; => '(2 4 8 16 32)
(--iterate (* it it) 2 5) ;; => '(2 4 16 256 65536)
Build a list from seed
using fun
.
This is "dual" operation to -reduce-r
: while -reduce-r
consumes a list to produce a single value, -unfold
takes a
seed value and builds a (potentially infinite!) list.
fun
should return nil
to stop the generating process, or a
cons (a
. b
), where a
will be prepended to the result and b
is
the new seed.
(-unfold (lambda (x) (unless (= x 0) (cons x (1- x)))) 10) ;; => '(10 9 8 7 6 5 4 3 2 1)
(--unfold (when it (cons it (cdr it))) '(1 2 3 4)) ;; => '((1 2 3 4) (2 3 4) (3 4) (4))
(--unfold (when it (cons it (butlast it))) '(1 2 3 4)) ;; => '((1 2 3 4) (1 2 3) (1 2) (1))
Return t if (pred
x) is non-nil for any x in list
, else nil.
Alias: -any-p
, -some?
, -some-p
(-any? 'even? '(1 2 3)) ;; => t
(-any? 'even? '(1 3 5)) ;; => nil
(-any? 'null '(1 3 5)) ;; => nil
Return t if (pred
x) is non-nil for all x in list
, else nil.
Alias: -all-p
, -every?
, -every-p
(-all? 'even? '(1 2 3)) ;; => nil
(-all? 'even? '(2 4 6)) ;; => t
(--all? (= 0 (% it 2)) '(2 4 6)) ;; => t
Return t if (pred
x) is nil for all x in list
, else nil.
Alias: -none-p
(-none? 'even? '(1 2 3)) ;; => nil
(-none? 'even? '(1 3 5)) ;; => t
(--none? (= 0 (% it 2)) '(1 2 3)) ;; => nil
Return t
if at least one item of list
matches pred
and at least one item of list
does not match pred
.
Return nil
both if all items match the predicate or if none of the items match the predicate.
Alias: -only-some-p
(-only-some? 'even? '(1 2 3)) ;; => t
(-only-some? 'even? '(1 3 5)) ;; => nil
(-only-some? 'even? '(2 4 6)) ;; => nil
Return non-nil if list
contains element
.
The test for equality is done with equal
, or with -compare-fn
if that's non-nil.
Alias: -contains-p
(-contains? '(1 2 3) 1) ;; => t
(-contains? '(1 2 3) 2) ;; => t
(-contains? '(1 2 3) 4) ;; => nil
Return true if list
and list2
has the same items.
The order of the elements in the lists does not matter.
Alias: -same-items-p
(-same-items? '(1 2 3) '(1 2 3)) ;; => t
(-same-items? '(1 2 3) '(3 2 1)) ;; => t
(-same-items? '(1 2 3) '(1 2 3 4)) ;; => nil
Return non-nil if prefix
is a prefix of list
.
Alias: -is-prefix-p
.
(-is-prefix? '(1 2 3) '(1 2 3 4 5)) ;; => t
(-is-prefix? '(1 2 3 4 5) '(1 2 3)) ;; => nil
(-is-prefix? '(1 3) '(1 2 3 4 5)) ;; => nil
Return non-nil if suffix
is a suffix of list
.
Alias: -is-suffix-p
.
(-is-suffix? '(3 4 5) '(1 2 3 4 5)) ;; => t
(-is-suffix? '(1 2 3 4 5) '(3 4 5)) ;; => nil
(-is-suffix? '(3 5) '(1 2 3 4 5)) ;; => nil
Return non-nil if infix
is infix of list
.
This operation runs in O(n^2) time
Alias: -is-infix-p
(-is-infix? '(1 2 3) '(1 2 3 4 5)) ;; => t
(-is-infix? '(2 3 4) '(1 2 3 4 5)) ;; => t
(-is-infix? '(3 4 5) '(1 2 3 4 5)) ;; => t
Return non-nil if obj
is a true cons pair.
That is, a cons (a
. b
) where b
is not a list.
Alias: -cons-pair-p
.
(-cons-pair? '(1 . 2)) ;; => t
(-cons-pair? '(1 2)) ;; => nil
(-cons-pair? '(1)) ;; => nil
Functions partitioning the input list into a list of lists.
Split list
into two sublists after the n
th element.
The result is a list of two elements (take
drop
) where take
is a
new list of the first n
elements of list
, and drop
is the
remaining elements of list
(not a copy). take
and drop
are like
the results of -take
and -drop
, respectively, but the split
is done in a single list traversal.
(-split-at 3 '(1 2 3 4 5)) ;; => '((1 2 3) (4 5))
(-split-at 17 '(1 2 3 4 5)) ;; => '((1 2 3 4 5) nil)
(-split-at 0 '(1 2 3 4 5)) ;; => '(nil (1 2 3 4 5))
Return a list of ((-take-while pred
list
) (-drop-while pred
list
)), in no more than one pass through the list.
(-split-with 'even? '(1 2 3 4)) ;; => '(nil (1 2 3 4))
(-split-with 'even? '(2 4 5 6)) ;; => '((2 4) (5 6))
(--split-with (< it 4) '(1 2 3 4 3 2 1)) ;; => '((1 2 3) (4 3 2 1))
Split the list
each time item
is found.
Unlike -partition-by
, the item
is discarded from the results.
Empty lists are also removed from the result.
Comparison is done by equal
.
See also -split-when
(-split-on '| '(Nil | Leaf a | Node [Tree a])) ;; => '((Nil) (Leaf a) (Node [Tree a]))
(-split-on ':endgroup '("a" "b" :endgroup "c" :endgroup "d" "e")) ;; => '(("a" "b") ("c") ("d" "e"))
(-split-on ':endgroup '("a" "b" :endgroup :endgroup "d" "e")) ;; => '(("a" "b") ("d" "e"))
Split the list
on each element where fn
returns non-nil.
Unlike -partition-by
, the "matched" element is discarded from
the results. Empty lists are also removed from the result.
This function can be thought of as a generalization of
split-string
.
(-split-when 'even? '(1 2 3 4 5 6)) ;; => '((1) (3) (5))
(-split-when 'even? '(1 2 3 4 6 8 9)) ;; => '((1) (3) (9))
(--split-when (memq it '(&optional &rest)) '(a b &optional c d &rest args)) ;; => '((a b) (c d) (args))
Return a list of ((-filter pred
list
) (-remove pred
list
)), in one pass through the list.
(-separate (lambda (num) (= 0 (% num 2))) '(1 2 3 4 5 6 7)) ;; => '((2 4 6) (1 3 5 7))
(--separate (< it 5) '(3 7 5 9 3 2 1 4 6)) ;; => '((3 3 2 1 4) (7 5 9 6))
(-separate 'cdr '((1 2) (1) (1 2 3) (4))) ;; => '(((1 2) (1 2 3)) ((1) (4)))
Return a new list with the items in list
grouped into n
-sized sublists.
If there are not enough items to make the last group n
-sized,
those items are discarded.
(-partition 2 '(1 2 3 4 5 6)) ;; => '((1 2) (3 4) (5 6))
(-partition 2 '(1 2 3 4 5 6 7)) ;; => '((1 2) (3 4) (5 6))
(-partition 3 '(1 2 3 4 5 6 7)) ;; => '((1 2 3) (4 5 6))
Return a new list with the items in list
grouped into n
-sized sublists.
The last group may contain less than n
items.
(-partition-all 2 '(1 2 3 4 5 6)) ;; => '((1 2) (3 4) (5 6))
(-partition-all 2 '(1 2 3 4 5 6 7)) ;; => '((1 2) (3 4) (5 6) (7))
(-partition-all 3 '(1 2 3 4 5 6 7)) ;; => '((1 2 3) (4 5 6) (7))
Return a new list with the items in list
grouped into n
-sized sublists at offsets step
apart.
If there are not enough items to make the last group n
-sized,
those items are discarded.
(-partition-in-steps 2 1 '(1 2 3 4)) ;; => '((1 2) (2 3) (3 4))
(-partition-in-steps 3 2 '(1 2 3 4)) ;; => '((1 2 3))
(-partition-in-steps 3 2 '(1 2 3 4 5)) ;; => '((1 2 3) (3 4 5))
Return a new list with the items in list
grouped into n
-sized sublists at offsets step
apart.
The last groups may contain less than n
items.
(-partition-all-in-steps 2 1 '(1 2 3 4)) ;; => '((1 2) (2 3) (3 4) (4))
(-partition-all-in-steps 3 2 '(1 2 3 4)) ;; => '((1 2 3) (3 4))
(-partition-all-in-steps 3 2 '(1 2 3 4 5)) ;; => '((1 2 3) (3 4 5) (5))
Apply fn
to each item in list
, splitting it each time fn
returns a new value.
(-partition-by 'even? '()) ;; => '()
(-partition-by 'even? '(1 1 2 2 2 3 4 6 8)) ;; => '((1 1) (2 2 2) (3) (4 6 8))
(--partition-by (< it 3) '(1 2 3 4 3 2 1)) ;; => '((1 2) (3 4 3) (2 1))
Apply fn
to the first item in list
. That is the header
value. Apply fn
to each item in list
, splitting it each time fn
returns the header value, but only after seeing at least one
other value (the body).
(--partition-by-header (= it 1) '(1 2 3 1 2 1 2 3 4)) ;; => '((1 2 3) (1 2) (1 2 3 4))
(--partition-by-header (> it 0) '(1 2 0 1 0 1 2 3 0)) ;; => '((1 2 0) (1 0) (1 2 3 0))
(-partition-by-header 'even? '(2 1 1 1 4 1 3 5 6 6 1)) ;; => '((2 1 1 1) (4 1 3 5) (6 6 1))
Partition directly after each time pred
is true on an element of list
.
(-partition-after-pred #'booleanp '()) ;; => '()
(-partition-after-pred #'booleanp '(t t)) ;; => '((t) (t))
(-partition-after-pred #'booleanp '(0 0 t t 0 t)) ;; => '((0 0 t) (t) (0 t))
Partition directly before each time pred
is true on an element of list
.
(-partition-before-pred #'booleanp '()) ;; => '()
(-partition-before-pred #'booleanp '(0 t)) ;; => '((0) (t))
(-partition-before-pred #'booleanp '(0 0 t 0 t t)) ;; => '((0 0) (t 0) (t) (t))
Partition directly before each time item
appears in list
.
(-partition-before-item 3 '()) ;; => '()
(-partition-before-item 3 '(1)) ;; => '((1))
(-partition-before-item 3 '(3)) ;; => '((3))
Partition directly after each time item
appears in list
.
(-partition-after-item 3 '()) ;; => '()
(-partition-after-item 3 '(1)) ;; => '((1))
(-partition-after-item 3 '(3)) ;; => '((3))
Separate list
into an alist whose keys are fn
applied to the
elements of list
. Keys are compared by equal
.
(-group-by 'even? '()) ;; => '()
(-group-by 'even? '(1 1 2 2 2 3 4 6 8)) ;; => '((nil 1 1 3) (t 2 2 2 4 6 8))
(--group-by (car (split-string it "/")) '("a/b" "c/d" "a/e")) ;; => '(("a" "a/b" "a/e") ("c" "c/d"))
Return indices of elements based on predicates, sort elements by indices etc.
Return the index of the first element in the given list
which
is equal to the query element elem
, or nil if there is no
such element.
(-elem-index 2 '(6 7 8 2 3 4)) ;; => 3
(-elem-index "bar" '("foo" "bar" "baz")) ;; => 1
(-elem-index '(1 2) '((3) (5 6) (1 2) nil)) ;; => 2
Return the indices of all elements in list
equal to the query
element elem
, in ascending order.
(-elem-indices 2 '(6 7 8 2 3 4 2 1)) ;; => '(3 6)
(-elem-indices "bar" '("foo" "bar" "baz")) ;; => '(1)
(-elem-indices '(1 2) '((3) (1 2) (5 6) (1 2) nil)) ;; => '(1 3)
Take a predicate pred
and a list
and return the index of the
first element in the list satisfying the predicate, or nil if
there is no such element.
See also -first
.
(-find-index 'even? '(2 4 1 6 3 3 5 8)) ;; => 0
(--find-index (< 5 it) '(2 4 1 6 3 3 5 8)) ;; => 3
(-find-index (-partial 'string-lessp "baz") '("bar" "foo" "baz")) ;; => 1
Take a predicate pred
and a list
and return the index of the
last element in the list satisfying the predicate, or nil if
there is no such element.
See also -last
.
(-find-last-index 'even? '(2 4 1 6 3 3 5 8)) ;; => 7
(--find-last-index (< 5 it) '(2 7 1 6 3 8 5 2)) ;; => 5
(-find-last-index (-partial 'string-lessp "baz") '("q" "foo" "baz")) ;; => 1
Return the indices of all elements in list
satisfying the
predicate pred
, in ascending order.
(-find-indices 'even? '(2 4 1 6 3 3 5 8)) ;; => '(0 1 3 7)
(--find-indices (< 5 it) '(2 4 1 6 3 3 5 8)) ;; => '(3 7)
(-find-indices (-partial 'string-lessp "baz") '("bar" "foo" "baz")) ;; => '(1)
Grade elements of list
using comparator
relation.
This yields a permutation vector such that applying this
permutation to list
sorts it in ascending order.
(-grade-up #'< '(3 1 4 2 1 3 3)) ;; => '(1 4 3 0 5 6 2)
(let ((l '(3 1 4 2 1 3 3))) (-select-by-indices (-grade-up #'< l) l)) ;; => '(1 1 2 3 3 3 4)
Grade elements of list
using comparator
relation.
This yields a permutation vector such that applying this
permutation to list
sorts it in descending order.
(-grade-down #'< '(3 1 4 2 1 3 3)) ;; => '(2 0 5 6 3 1 4)
(let ((l '(3 1 4 2 1 3 3))) (-select-by-indices (-grade-down #'< l) l)) ;; => '(4 3 3 3 2 1 1)
Operations pretending lists are sets.
Return a new list containing the elements of list
and elements of list2
that are not in list
.
The test for equality is done with equal
,
or with -compare-fn
if that's non-nil.
(-union '(1 2 3) '(3 4 5)) ;; => '(1 2 3 4 5)
(-union '(1 2 3 4) '()) ;; => '(1 2 3 4)
(-union '(1 1 2 2) '(3 2 1)) ;; => '(1 1 2 2 3)
Return a new list with only the members of list
that are not in list2
.
The test for equality is done with equal
,
or with -compare-fn
if that's non-nil.
(-difference '() '()) ;; => '()
(-difference '(1 2 3) '(4 5 6)) ;; => '(1 2 3)
(-difference '(1 2 3 4) '(3 4 5 6)) ;; => '(1 2)
Return a new list containing only the elements that are members of both list
and list2
.
The test for equality is done with equal
,
or with -compare-fn
if that's non-nil.
(-intersection '() '()) ;; => '()
(-intersection '(1 2 3) '(4 5 6)) ;; => '()
(-intersection '(1 2 3 4) '(3 4 5 6)) ;; => '(3 4)
Return the power set of list
.
(-powerset '()) ;; => '(nil)
(-powerset '(x y z)) ;; => '((x y z) (x y) (x z) (x) (y z) (y) (z) nil)
Return the permutations of list
.
(-permutations '()) ;; => '(nil)
(-permutations '(1 2)) ;; => '((1 2) (2 1))
(-permutations '(a b c)) ;; => '((a b c) (a c b) (b a c) (b c a) (c a b) (c b a))
Return a new list with all duplicates removed.
The test for equality is done with equal
,
or with -compare-fn
if that's non-nil.
Alias: -uniq
(-distinct '()) ;; => '()
(-distinct '(1 2 2 4)) ;; => '(1 2 4)
(-distinct '(t t t)) ;; => '(t)
Other list functions not fit to be classified elsewhere.
Rotate list
n
places to the right. With n
negative, rotate to the left.
The time complexity is O(n).
(-rotate 3 '(1 2 3 4 5 6 7)) ;; => '(5 6 7 1 2 3 4)
(-rotate -3 '(1 2 3 4 5 6 7)) ;; => '(4 5 6 7 1 2 3)
(-rotate 16 '(1 2 3 4 5 6 7)) ;; => '(6 7 1 2 3 4 5)
Return a new list of length n
with each element being x
.
Return nil if n
is less than 1.
(-repeat 3 :a) ;; => '(:a :a :a)
(-repeat 1 :a) ;; => '(:a)
(-repeat 0 :a) ;; => nil
Make a new list from the elements of args
.
The last 2 elements of args
are used as the final cons of the
result, so if the final element of args
is not a list, the result
is a dotted list. With no args
, return nil.
(-cons* 1 2) ;; => '(1 . 2)
(-cons* 1 2 3) ;; => '(1 2 . 3)
(-cons* 1) ;; => 1
Append elem
to the end of the list.
This is like cons
, but operates on the end of list.
If elements
is non nil, append these to the list as well.
(-snoc '(1 2 3) 4) ;; => '(1 2 3 4)
(-snoc '(1 2 3) 4 5 6) ;; => '(1 2 3 4 5 6)
(-snoc '(1 2 3) '(4 5 6)) ;; => '(1 2 3 (4 5 6))
Return a new list of all elements in list
separated by sep
.
(-interpose "-" '()) ;; => '()
(-interpose "-" '("a")) ;; => '("a")
(-interpose "-" '("a" "b" "c")) ;; => '("a" "-" "b" "-" "c")
Return a new list of the first item in each list, then the second etc.
(-interleave '(1 2) '("a" "b")) ;; => '(1 "a" 2 "b")
(-interleave '(1 2) '("a" "b") '("A" "B")) ;; => '(1 "a" "A" 2 "b" "B")
(-interleave '(1 2 3) '("a" "b")) ;; => '(1 "a" 2 "b")
Return a list containing count
numbers.
Starts from start
and adds step
each time. The default start
is
zero, the default step
is 1.
This function takes its name from the corresponding primitive in
the apl
language.
(-iota 6) ;; => '(0 1 2 3 4 5)
(-iota 4 2.5 -2) ;; => '(2.5 0.5 -1.5 -3.5)
(-iota -1) ;; Error
Zip the two lists list1
and list2
using a function fn
. This
function is applied pairwise taking as first argument element of
list1
and as second argument element of list2
at corresponding
position.
The anaphoric form --zip-with
binds the elements from list1
as symbol it
,
and the elements from list2
as symbol other
.
(-zip-with '+ '(1 2 3) '(4 5 6)) ;; => '(5 7 9)
(-zip-with 'cons '(1 2 3) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))
(--zip-with (concat it " and " other) '("Batman" "Jekyll") '("Robin" "Hyde")) ;; => '("Batman and Robin" "Jekyll and Hyde")
Zip lists
together. Group the head of each list, followed by the
second elements of each list, and so on. The lengths of the returned
groupings are equal to the length of the shortest input list.
If two lists are provided as arguments, return the groupings as a list of cons cells. Otherwise, return the groupings as a list of lists.
Use -zip-lists
if you need the return value to always be a list
of lists.
Alias: -zip-pair
See also: -zip-lists
(-zip '(1 2 3) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))
(-zip '(1 2 3) '(4 5 6 7)) ;; => '((1 . 4) (2 . 5) (3 . 6))
(-zip '(1 2) '(3 4 5) '(6)) ;; => '((1 3 6))
Zip lists
together. Group the head of each list, followed by the
second elements of each list, and so on. The lengths of the returned
groupings are equal to the length of the shortest input list.
The return value is always list of lists, which is a difference
from -zip-pair
which returns a cons-cell in case two input
lists are provided.
See also: -zip
(-zip-lists '(1 2 3) '(4 5 6)) ;; => '((1 4) (2 5) (3 6))
(-zip-lists '(1 2 3) '(4 5 6 7)) ;; => '((1 4) (2 5) (3 6))
(-zip-lists '(1 2) '(3 4 5) '(6)) ;; => '((1 3 6))
Zip lists
, with fill-value
padded onto the shorter lists. The
lengths of the returned groupings are equal to the length of the
longest input list.
(-zip-fill 0 '(1 2 3 4 5) '(6 7 8 9)) ;; => '((1 . 6) (2 . 7) (3 . 8) (4 . 9) (5 . 0))
Unzip lists
.
This works just like -zip
but takes a list of lists instead of
a variable number of arguments, such that
(-unzip (-zip `l1` `l2` `l3` ...))
is identity (given that the lists are the same length).
Note in particular that calling this on a list of two lists will return a list of cons-cells such that the above identity works.
See also: -zip
(-unzip (-zip '(1 2 3) '(a b c) '("e" "f" "g"))) ;; => '((1 2 3) (a b c) ("e" "f" "g"))
(-unzip '((1 2) (3 4) (5 6) (7 8) (9 10))) ;; => '((1 3 5 7 9) (2 4 6 8 10))
(-unzip '((1 2) (3 4))) ;; => '((1 . 3) (2 . 4))
Return an infinite circular copy of list
.
The returned list cycles through the elements of list
and repeats
from the beginning.
(-take 5 (-cycle '(1 2 3))) ;; => '(1 2 3 1 2)
(-take 7 (-cycle '(1 "and" 3))) ;; => '(1 "and" 3 1 "and" 3 1)
(-zip (-cycle '(1 2 3)) '(1 2)) ;; => '((1 . 1) (2 . 2))
Appends fill-value
to the end of each list in lists
such that they
will all have the same length.
(-pad 0 '()) ;; => '(nil)
(-pad 0 '(1)) ;; => '((1))
(-pad 0 '(1 2 3) '(4 5)) ;; => '((1 2 3) (4 5 0))
Compute outer product of lists
using function fn
.
The function fn
should have the same arity as the number of
supplied lists.
The outer product is computed by applying fn to all possible combinations created by taking one element from each list in order. The dimension of the result is (length lists).
See also: -table-flat
(-table '* '(1 2 3) '(1 2 3)) ;; => '((1 2 3) (2 4 6) (3 6 9))
(-table (lambda (a b) (-sum (-zip-with '* a b))) '((1 2) (3 4)) '((1 3) (2 4))) ;; => '((7 15) (10 22))
(apply '-table 'list (-repeat 3 '(1 2))) ;; => '((((1 1 1) (2 1 1)) ((1 2 1) (2 2 1))) (((1 1 2) (2 1 2)) ((1 2 2) (2 2 2))))
Compute flat outer product of lists
using function fn
.
The function fn
should have the same arity as the number of
supplied lists.
The outer product is computed by applying fn to all possible combinations created by taking one element from each list in order. The results are flattened, ignoring the tensor structure of the result. This is equivalent to calling:
(-flatten-n (1- (length lists)) (apply '-table fn lists))
but the implementation here is much more efficient.
See also: -flatten-n
, -table
(-table-flat 'list '(1 2 3) '(a b c)) ;; => '((1 a) (2 a) (3 a) (1 b) (2 b) (3 b) (1 c) (2 c) (3 c))
(-table-flat '* '(1 2 3) '(1 2 3)) ;; => '(1 2 3 2 4 6 3 6 9)
(apply '-table-flat 'list (-repeat 3 '(1 2))) ;; => '((1 1 1) (2 1 1) (1 2 1) (2 2 1) (1 1 2) (2 1 2) (1 2 2) (2 2 2))
Return the first item in list
for which pred
returns non-nil.
Return nil if no such element is found.
To get the first item in the list no questions asked, use car
.
Alias: -find
.
This function's anaphoric counterpart is --first
.
(-first #'natnump '(-1 0 1)) ;; => 0
(-first #'null '(1 2 3)) ;; => nil
(--first (> it 2) '(1 2 3)) ;; => 3
Return (pred
x) for the first list
item where (pred
x) is non-nil, else nil.
Alias: -any
.
This function's anaphoric counterpart is --some
.
(-some (lambda (s) (string-match-p "x" s)) '("foo" "axe" "xor")) ;; => 1
(-some (lambda (s) (string-match-p "x" s)) '("foo" "bar" "baz")) ;; => nil
(--some (member 'foo it) '((foo bar) (baz))) ;; => '(foo bar)
Return the last x in list
where (pred
x) is non-nil, else nil.
(-last 'even? '(1 2 3 4 5 6 3 3 3)) ;; => 6
(-last 'even? '(1 3 7 5 9)) ;; => nil
(--last (> (length it) 3) '("a" "looong" "word" "and" "short" "one")) ;; => "short"
Return the first item of list
, or nil on an empty list.
See also: -second-item
, -last-item
.
(-first-item '(1 2 3)) ;; => 1
(-first-item nil) ;; => nil
(let ((list (list 1 2 3))) (setf (-first-item list) 5) list) ;; => '(5 2 3)
Return the second item of list
, or nil if list
is too short.
See also: -third-item
.
(-second-item '(1 2 3)) ;; => 2
(-second-item nil) ;; => nil
Return the third item of list
, or nil if list
is too short.
See also: -fourth-item
.
(-third-item '(1 2 3)) ;; => 3
(-third-item nil) ;; => nil
Return the fourth item of list
, or nil if list
is too short.
See also: -fifth-item
.
(-fourth-item '(1 2 3 4)) ;; => 4
(-fourth-item nil) ;; => nil
Return the fifth item of list
, or nil if list
is too short.
See also: -last-item
.
(-fifth-item '(1 2 3 4 5)) ;; => 5
(-fifth-item nil) ;; => nil
Return the last item of list
, or nil on an empty list.
(-last-item '(1 2 3)) ;; => 3
(-last-item nil) ;; => nil
(let ((list (list 1 2 3))) (setf (-last-item list) 5) list) ;; => '(1 2 5)
Return a list of all items in list except for the last.
(-butlast '(1 2 3)) ;; => '(1 2)
(-butlast '(1 2)) ;; => '(1)
(-butlast '(1)) ;; => nil
Sort list
, stably, comparing elements using comparator
.
Return the sorted list. list
is not
modified by side effects.
comparator
is called with two elements of list
, and should return non-nil
if the first element should sort before the second.
(-sort '< '(3 1 2)) ;; => '(1 2 3)
(-sort '> '(3 1 2)) ;; => '(3 2 1)
(--sort (< it other) '(3 1 2)) ;; => '(1 2 3)
Ensure arg
is a list.
If arg
is already a list, return it as is (not a copy).
Otherwise, return a new list with arg
as its only element.
Another supported calling convention is (-list &rest args
).
In this case, if arg
is not a list, a new list with all of
args
as elements is returned. This use is supported for
backward compatibility and is otherwise deprecated.
(-list 1) ;; => '(1)
(-list nil) ;; => nil
(-list '(1 2 3)) ;; => '(1 2 3)
Compute the (least) fixpoint of fn
with initial input list
.
fn
is called at least once, results are compared with equal
.
(-fix (lambda (l) (-non-nil (--mapcat (-split-at (/ (length it) 2) it) l))) '((1 2 3))) ;; => '((1) (2) (3))
(let ((l '((starwars scifi) (jedi starwars warrior)))) (--fix (-uniq (--mapcat (cons it (cdr (assq it l))) it)) '(jedi book))) ;; => '(jedi starwars warrior scifi book)
Functions pretending lists are trees.
Return a sequence of the nodes in tree
, in depth-first search order.
branch
is a predicate of one argument that returns non-nil if the
passed argument is a branch, that is, a node that can have children.
children
is a function of one argument that returns the children
of the passed branch node.
Non-branch nodes are simply copied.
(-tree-seq 'listp 'identity '(1 (2 3) 4 (5 (6 7)))) ;; => '((1 (2 3) 4 (5 (6 7))) 1 (2 3) 2 3 4 (5 (6 7)) 5 (6 7) 6 7)
(-tree-seq 'listp 'reverse '(1 (2 3) 4 (5 (6 7)))) ;; => '((1 (2 3) 4 (5 (6 7))) (5 (6 7)) (6 7) 7 6 5 4 (2 3) 3 2 1)
(--tree-seq (vectorp it) (append it nil) [1 [2 3] 4 [5 [6 7]]]) ;; => '([1 [2 3] 4 [5 [6 7]]] 1 [2 3] 2 3 4 [5 [6 7]] 5 [6 7] 6 7)
Apply fn
to each element of tree
while preserving the tree structure.
(-tree-map '1+ '(1 (2 3) (4 (5 6) 7))) ;; => '(2 (3 4) (5 (6 7) 8))
(-tree-map '(lambda (x) (cons x (expt 2 x))) '(1 (2 3) 4)) ;; => '((1 . 2) ((2 . 4) (3 . 8)) (4 . 16))
(--tree-map (length it) '("<body>" ("<p>" "text" "</p>") "</body>")) ;; => '(6 (3 4 4) 7)
Call fun
on each node of tree
that satisfies pred
.
If pred
returns nil, continue descending down this node. If pred
returns non-nil, apply fun
to this node and do not descend
further.
(-tree-map-nodes 'vectorp (lambda (x) (-sum (append x nil))) '(1 [2 3] 4 (5 [6 7] 8))) ;; => '(1 5 4 (5 13 8))
(-tree-map-nodes 'keywordp (lambda (x) (symbol-name x)) '(1 :foo 4 ((5 6 :bar) :baz 8))) ;; => '(1 ":foo" 4 ((5 6 ":bar") ":baz" 8))
(--tree-map-nodes (eq (car-safe it) 'add-mode) (-concat it (list :mode 'emacs-lisp-mode)) '(with-mode emacs-lisp-mode (foo bar) (add-mode a b) (baz (add-mode c d)))) ;; => '(with-mode emacs-lisp-mode (foo bar) (add-mode a b :mode emacs-lisp-mode) (baz (add-mode c d :mode emacs-lisp-mode)))
Use fn
to reduce elements of list tree
.
If elements of tree
are lists themselves, apply the reduction recursively.
fn
is first applied to first element of the list and second
element, then on this result and third element from the list etc.
See -reduce-r
for how exactly are lists of zero or one element handled.
(-tree-reduce '+ '(1 (2 3) (4 5))) ;; => 15
(-tree-reduce 'concat '("strings" (" on" " various") ((" levels")))) ;; => "strings on various levels"
(--tree-reduce (cond ((stringp it) (concat it " " acc)) (t (let ((sn (symbol-name it))) (concat "<" sn ">" acc "</" sn ">")))) '(body (p "some words") (div "more" (b "bold") "words"))) ;; => "<body><p>some words</p> <div>more <b>bold</b> words</div></body>"
Use fn
to reduce elements of list tree
.
If elements of tree
are lists themselves, apply the reduction recursively.
fn
is first applied to init-value
and first element of the list,
then on this result and second element from the list etc.
The initial value is ignored on cons pairs as they always contain two elements.
(-tree-reduce-from '+ 1 '(1 (1 1) ((1)))) ;; => 8
(--tree-reduce-from (-concat acc (list it)) nil '(1 (2 3 (4 5)) (6 7))) ;; => '((7 6) ((5 4) 3 2) 1)
Apply fn
to each element of tree
, and make a list of the results.
If elements of tree
are lists themselves, apply fn
recursively to
elements of these nested lists.
Then reduce the resulting lists using folder
and initial value
init-value
. See -reduce-r-from
.
This is the same as calling -tree-reduce
after -tree-map
but is twice as fast as it only traverse the structure once.
(-tree-mapreduce 'list 'append '(1 (2 (3 4) (5 6)) (7 (8 9)))) ;; => '(1 2 3 4 5 6 7 8 9)
(--tree-mapreduce 1 (+ it acc) '(1 (2 (4 9) (2 1)) (7 (4 3)))) ;; => 9
(--tree-mapreduce 0 (max acc (1+ it)) '(1 (2 (4 9) (2 1)) (7 (4 3)))) ;; => 3
Apply fn
to each element of tree
, and make a list of the results.
If elements of tree
are lists themselves, apply fn
recursively to
elements of these nested lists.
Then reduce the resulting lists using folder
and initial value
init-value
. See -reduce-r-from
.
This is the same as calling -tree-reduce-from
after -tree-map
but is twice as fast as it only traverse the structure once.
(-tree-mapreduce-from 'identity '* 1 '(1 (2 (3 4) (5 6)) (7 (8 9)))) ;; => 362880
(--tree-mapreduce-from (+ it it) (cons it acc) nil '(1 (2 (4 9) (2 1)) (7 (4 3)))) ;; => '(2 (4 (8 18) (4 2)) (14 (8 6)))
(concat "{" (--tree-mapreduce-from (cond ((-cons-pair? it) (concat (symbol-name (car it)) " -> " (symbol-name (cdr it)))) (t (concat (symbol-name it) " : {"))) (concat it (unless (or (equal acc "}") (equal (substring it (1- (length it))) "{")) ", ") acc) "}" '((elisp-mode (foo (bar . booze)) (baz . qux)) (c-mode (foo . bla) (bum . bam))))) ;; => "{elisp-mode : {foo : {bar -> booze}, baz -> qux}, c-mode : {foo -> bla, bum -> bam}}"
Create a deep copy of list
.
The new list has the same elements and structure but all cons are
replaced with new ones. This is useful when you need to clone a
structure such as plist or alist.
(let* ((a '(1 2 3)) (b (-clone a))) (nreverse a) b) ;; => '(1 2 3)
Thread the expr through the forms. Insert x
as the second item
in the first form, making a list of it if it is not a list
already. If there are more forms, insert the first form as the
second item in second form, etc.
(-> '(2 3 5)) ;; => '(2 3 5)
(-> '(2 3 5) (append '(8 13))) ;; => '(2 3 5 8 13)
(-> '(2 3 5) (append '(8 13)) (-slice 1 -1)) ;; => '(3 5 8)
Thread the expr through the forms. Insert x
as the last item
in the first form, making a list of it if it is not a list
already. If there are more forms, insert the first form as the
last item in second form, etc.
(->> '(1 2 3) (-map 'square)) ;; => '(1 4 9)
(->> '(1 2 3) (-map 'square) (-remove 'even?)) ;; => '(1 9)
(->> '(1 2 3) (-map 'square) (-reduce '+)) ;; => 14
Starting with the value of x
, thread each expression through forms
.
Insert x
at the position signified by the symbol it
in the first
form. If there are more forms, insert the first form at the position
signified by it
in in second form, etc.
(--> "def" (concat "abc" it "ghi")) ;; => "abcdefghi"
(--> "def" (concat "abc" it "ghi") (upcase it)) ;; => "ABCDEFGHI"
(--> "def" (concat "abc" it "ghi") upcase) ;; => "ABCDEFGHI"
Starting with value
, thread variable
through forms
.
In the first form, bind variable
to value
. In the second form, bind
variable
to the result of the first form, and so forth.
(-as-> 3 my-var (1+ my-var) (list my-var) (mapcar (lambda (ele) (* 2 ele)) my-var)) ;; => '(8)
(-as-> 3 my-var 1+) ;; => 4
(-as-> 3 my-var) ;; => 3
When expr is non-nil, thread it through the first form (via ->
),
and when that result is non-nil, through the next form, etc.
(-some-> '(2 3 5)) ;; => '(2 3 5)
(-some-> 5 square) ;; => 25
(-some-> 5 even? square) ;; => nil
When expr is non-nil, thread it through the first form (via ->>
),
and when that result is non-nil, through the next form, etc.
(-some->> '(1 2 3) (-map 'square)) ;; => '(1 4 9)
(-some->> '(1 3 5) (-last 'even?) (+ 100)) ;; => nil
(-some->> '(2 4 6) (-last 'even?) (+ 100)) ;; => 106
Thread expr
through forms
via -->
, while the result is non-nil.
When expr
evaluates to non-nil, thread the result through the
first of forms
, and when that result is non-nil, thread it
through the next form, etc.
(-some--> "def" (concat "abc" it "ghi")) ;; => "abcdefghi"
(-some--> nil (concat "abc" it "ghi")) ;; => nil
(-some--> '(0 1) (-remove #'natnump it) (append it it) (-map #'1+ it)) ;; => '()
Evaluate init
and pass it as argument to forms
with ->
.
The result
of evaluating init
is threaded through each of forms
individually using ->
, which see. The return value is result
,
which forms
may have modified by side effect.
(-doto (list 1 2 3) pop pop) ;; => '(3)
(-doto (cons 1 2) (setcar 3) (setcdr 4)) ;; => '(3 . 4)
(gethash 'k (--doto (make-hash-table) (puthash 'k 'v it))) ;; => 'v
Convenient versions of let
and let*
constructs combined with flow control.
If val
evaluates to non-nil, bind it to var
and execute body.
Note: binding is done according to -let
.
(-when-let (match-index (string-match "d" "abcd")) (+ match-index 2)) ;; => 5
(-when-let ((&plist :foo foo) (list :foo "foo")) foo) ;; => "foo"
(-when-let ((&plist :foo foo) (list :bar "bar")) foo) ;; => nil
If all vals
evaluate to true, bind them to their corresponding
vars
and execute body. vars-vals
should be a list of (var
val
)
pairs.
Note: binding is done according to -let*
. vals
are evaluated
sequentially, and evaluation stops after the first nil val
is
encountered.
(-when-let* ((x 5) (y 3) (z (+ y 4))) (+ x y z)) ;; => 15
(-when-let* ((x 5) (y nil) (z 7)) (+ x y z)) ;; => nil
If val
evaluates to non-nil, bind it to var
and do then
,
otherwise do else
.
Note: binding is done according to -let
.
(-if-let (match-index (string-match "d" "abc")) (+ match-index 3) 7) ;; => 7
(--if-let (even? 4) it nil) ;; => t
If all vals
evaluate to true, bind them to their corresponding
vars
and do then
, otherwise do else
. vars-vals
should be a list
of (var
val
) pairs.
Note: binding is done according to -let*
. vals
are evaluated
sequentially, and evaluation stops after the first nil val
is
encountered.
(-if-let* ((x 5) (y 3) (z 7)) (+ x y z) "foo") ;; => 15
(-if-let* ((x 5) (y nil) (z 7)) (+ x y z) "foo") ;; => "foo"
(-if-let* (((_ _ x) '(nil nil 7))) x) ;; => 7
Bind variables according to varlist
then eval body
.
varlist
is a list of lists of the form (pattern
source
). Each
pattern
is matched against the source
"structurally". source
is only evaluated once for each pattern
. Each pattern
is matched
recursively, and can therefore contain sub-patterns which are
matched against corresponding sub-expressions of source
.
All the SOURCEs are evalled before any symbols are bound (i.e. "in parallel").
If varlist
only contains one (pattern
source
) element, you can
optionally specify it using a vector and discarding the
outer-most parens. Thus
(-let ((`pattern` `source`)) ...)
becomes
(-let [`pattern` `source`] ...).
-let
uses a convention of not binding places (symbols) starting
with _ whenever it's possible. You can use this to skip over
entries you don't care about. However, this is not always
possible (as a result of implementation) and these symbols might
get bound to undefined values.
Following is the overview of supported patterns. Remember that patterns can be matched recursively, so every a, b, aK in the following can be a matching construct and not necessarily a symbol/variable.
Symbol:
a - bind the `source` to `a`. This is just like regular `let`.
Conses and lists:
(a) - bind `car` of cons/list to `a`
(a . b) - bind car of cons to `a` and `cdr` to `b`
(a b) - bind car of list to `a` and `cadr` to `b`
(a1 a2 a3 ...) - bind 0th car of list to `a1`, 1st to `a2`, 2nd to `a3`...
(a1 a2 a3 ... aN . rest) - as above, but bind the `n`th cdr to `rest`.
Vectors:
[a] - bind 0th element of a non-list sequence to `a` (works with
vectors, strings, bit arrays...)
[a1 a2 a3 ...] - bind 0th element of non-list sequence to `a0`, 1st to
`a1`, 2nd to `a2`, ...
If the `pattern` is shorter than `source`, the values at
places not in `pattern` are ignored.
If the `pattern` is longer than `source`, an `error` is
thrown.
[a1 a2 a3 ... &rest rest] - as above, but bind the rest of
the sequence to `rest`. This is
conceptually the same as improper list
matching (a1 a2 ... aN . rest)
Key/value stores:
(&plist key0 a0 ... keyN aN) - bind value mapped by keyK in the
`source` plist to aK. If the
value is not found, aK is nil.
Uses `plist-get` to fetch values.
(&alist key0 a0 ... keyN aN) - bind value mapped by keyK in the
`source` alist to aK. If the
value is not found, aK is nil.
Uses `assoc` to fetch values.
(&hash key0 a0 ... keyN aN) - bind value mapped by keyK in the
`source` hash table to aK. If the
value is not found, aK is nil.
Uses `gethash` to fetch values.
Further, special keyword &keys supports "inline" matching of
plist-like key-value pairs, similarly to &keys keyword of
cl-defun
.
(a1 a2 ... aN &keys key1 b1 ... keyN bK)
This binds n
values from the list to a1 ... aN, then interprets
the cdr as a plist (see key/value matching above).
a
shorthand notation for kv-destructuring exists which allows the
patterns be optionally left out and derived from the key name in
the following fashion:
- a key :foo is converted into
foo
pattern, - a key 'bar is converted into
bar
pattern, - a key "baz" is converted into
baz
pattern.
That is, the entire value under the key is bound to the derived variable without any further destructuring.
This is possible only when the form following the key is not a valid pattern (i.e. not a symbol, a cons cell or a vector). Otherwise the matching proceeds as usual and in case of an invalid spec fails with an error.
Thus the patterns are normalized as follows:
;; derive all the missing patterns
(&plist :foo 'bar "baz") => (&plist :foo foo 'bar bar "baz" baz)
;; we can specify some but not others
(&plist :foo 'bar explicit-bar) => (&plist :foo foo 'bar explicit-bar)
;; nothing happens, we store :foo in x
(&plist :foo x) => (&plist :foo x)
;; nothing happens, we match recursively
(&plist :foo (a b c)) => (&plist :foo (a b c))
You can name the source using the syntax symbol
&as pattern
.
This syntax works with lists (proper or improper), vectors and
all types of maps.
(list &as a b c) (list 1 2 3)
binds a
to 1, b
to 2, c
to 3 and list
to (1 2 3).
Similarly:
(bounds &as beg . end) (cons 1 2)
binds beg
to 1, end
to 2 and bounds
to (1 . 2).
(items &as first . rest) (list 1 2 3)
binds first
to 1, rest
to (2 3) and items
to (1 2 3)
[vect &as _ b c] [1 2 3]
binds b
to 2, c
to 3 and vect
to [1 2 3] (_ avoids binding as usual).
(plist &as &plist :b b) (list :a 1 :b 2 :c 3)
binds b
to 2 and plist
to (:a 1 :b 2 :c 3). Same for &alist and &hash.
This is especially useful when we want to capture the result of a computation and destructure at the same time. Consider the form (function-returning-complex-structure) returning a list of two vectors with two items each. We want to capture this entire result and pass it to another computation, but at the same time we want to get the second item from each vector. We can achieve it with pattern
(result &as [_ a] [_ b]) (function-returning-complex-structure)
Note: Clojure programmers may know this feature as the ":as binding". The difference is that we put the &as at the front because we need to support improper list binding.
(-let (([a (b c) d] [1 (2 3) 4])) (list a b c d)) ;; => '(1 2 3 4)
(-let [(a b c . d) (list 1 2 3 4 5 6)] (list a b c d)) ;; => '(1 2 3 (4 5 6))
(-let [(&plist :foo foo :bar bar) (list :baz 3 :foo 1 :qux 4 :bar 2)] (list foo bar)) ;; => '(1 2)
Bind variables according to varlist
then eval body
.
varlist
is a list of lists of the form (pattern
source
). Each
pattern
is matched against the source
structurally. source
is
only evaluated once for each pattern
.
Each source
can refer to the symbols already bound by this
varlist
. This is useful if you want to destructure source
recursively but also want to name the intermediate structures.
See -let
for the list of all possible patterns.
(-let* (((a . b) (cons 1 2)) ((c . d) (cons 3 4))) (list a b c d)) ;; => '(1 2 3 4)
(-let* (((a . b) (cons 1 (cons 2 3))) ((c . d) b)) (list a b c d)) ;; => '(1 (2 . 3) 2 3)
(-let* (((&alist "foo" foo "bar" bar) (list (cons "foo" 1) (cons "bar" (list 'a 'b 'c)))) ((a b c) bar)) (list foo a b c bar)) ;; => '(1 a b c (a b c))
Return a lambda which destructures its input as match-form
and executes body
.
Note that you have to enclose the match-form
in a pair of parens,
such that:
(-lambda (x) body)
(-lambda (x y ...) body)
has the usual semantics of lambda
. Furthermore, these get
translated into normal lambda
, so there is no performance
penalty.
See -let
for a description of the destructuring mechanism.
(-map (-lambda ((x y)) (+ x y)) '((1 2) (3 4) (5 6))) ;; => '(3 7 11)
(-map (-lambda ([x y]) (+ x y)) '([1 2] [3 4] [5 6])) ;; => '(3 7 11)
(funcall (-lambda ((_ . a) (_ . b)) (-concat a b)) '(1 2 3) '(4 5 6)) ;; => '(2 3 5 6)
Bind each match-form
to the value of its val
.
match-form
destructuring is done according to the rules of -let
.
This macro allows you to bind multiple variables by destructuring the value, so for example:
(-setq (a b) x
(&plist :c c) plist)
expands roughly speaking to the following code
(setq a (car x)
b (cadr x)
c (plist-get plist :c))
Care is taken to only evaluate each val
once so that in case of
multiple assignments it does not cause unexpected side effects.
(let (a) (-setq a 1) a) ;; => 1
(let (a b) (-setq (a b) (list 1 2)) (list a b)) ;; => '(1 2)
(let (c) (-setq (&plist :c c) (list :c "c")) c) ;; => "c"
Functions iterating over lists for side effect only.
Call fn
on each element of list
.
Return nil; this function is intended for side effects.
Its anaphoric counterpart is --each
. For access to the current
element's index in list
, see -each-indexed
.
(let (l) (-each '(1 2 3) (lambda (x) (push x l))) l) ;; => '(3 2 1)
(let (l) (--each '(1 2 3) (push it l)) l) ;; => '(3 2 1)
(-each '(1 2 3) #'identity) ;; => nil
Call fn
on each item
in list
, while (pred
item
) is non-nil.
Once an item
is reached for which pred
returns nil, fn
is no
longer called. Return nil; this function is intended for side
effects.
Its anaphoric counterpart is --each-while
.
(let (l) (-each-while '(2 4 5 6) #'even? (lambda (x) (push x l))) l) ;; => '(4 2)
(let (l) (--each-while '(1 2 3 4) (< it 3) (push it l)) l) ;; => '(2 1)
(let ((s 0)) (--each-while '(1 3 4 5) (< it 5) (setq s (+ s it))) s) ;; => 8
Call fn
on each index and element of list
.
For each item
at index
in list
, call (funcall fn
index
item
).
Return nil; this function is intended for side effects.
See also: -map-indexed
.
(let (l) (-each-indexed '(a b c) (lambda (i x) (push (list x i) l))) l) ;; => '((c 2) (b 1) (a 0))
(let (l) (--each-indexed '(a b c) (push (list it it-index) l)) l) ;; => '((c 2) (b 1) (a 0))
(let (l) (--each-indexed nil (push it l)) l) ;; => nil
Call fn
on each element of list
in reversed order.
Return nil; this function is intended for side effects.
Its anaphoric counterpart is --each-r
.
(let (l) (-each-r '(1 2 3) (lambda (x) (push x l))) l) ;; => '(1 2 3)
(let (l) (--each-r '(1 2 3) (push it l)) l) ;; => '(1 2 3)
(-each-r '(1 2 3) #'identity) ;; => nil
Call fn
on each item
in reversed list
, while (pred
item
) is non-nil.
Once an item
is reached for which pred
returns nil, fn
is no
longer called. Return nil; this function is intended for side
effects.
Its anaphoric counterpart is --each-r-while
.
(let (l) (-each-r-while '(2 4 5 6) #'even? (lambda (x) (push x l))) l) ;; => '(6)
(let (l) (--each-r-while '(1 2 3 4) (>= it 3) (push it l)) l) ;; => '(3 4)
(let ((s 0)) (--each-r-while '(1 2 3 5) (> it 1) (setq s (+ s it))) s) ;; => 10
Call fn
num
times, presumably for side effects.
fn
is called with a single argument on successive integers
running from 0, inclusive, to num
, exclusive. fn
is not called
if num
is less than 1.
This function's anaphoric counterpart is --dotimes
.
(let (s) (-dotimes 3 (lambda (n) (push n s))) s) ;; => '(2 1 0)
(let (s) (-dotimes 0 (lambda (n) (push n s))) s) ;; => nil
(let (s) (--dotimes 5 (push it s)) s) ;; => '(4 3 2 1 0)
Destructive: Set cdr
to the cons of car
and cdr
.
(let (l) (!cons 5 l) l) ;; => '(5)
(let ((l '(3))) (!cons 5 l) l) ;; => '(5 3)
Destructive: Set list
to the cdr of list
.
(let ((l '(3))) (!cdr l) l) ;; => '()
(let ((l '(3 5))) (!cdr l) l) ;; => '(5)
These combinators require Emacs 24 for its lexical scope. So they are offered in a separate package: dash-functional
.
Take a function fn
and fewer than the normal arguments to fn
,
and return a fn that takes a variable number of additional args
.
When called, the returned function calls fn
with args
first and
then additional args.
(funcall (-partial '- 5) 3) ;; => 2
(funcall (-partial '+ 5 2) 3) ;; => 10
Takes a function fn
and fewer than the normal arguments to fn
,
and returns a fn that takes a variable number of additional args
.
When called, the returned function calls fn
with the additional
args first and then args
.
(funcall (-rpartial '- 5) 8) ;; => 3
(funcall (-rpartial '- 5 2) 10) ;; => 3
Takes a list of functions and returns a fn that is the juxtaposition of those fns. The returned fn takes a variable number of args, and returns a list containing the result of applying each fn to the args (left-to-right).
(funcall (-juxt '+ '-) 3 5) ;; => '(8 -2)
(-map (-juxt 'identity 'square) '(1 2 3)) ;; => '((1 1) (2 4) (3 9))
Takes a list of functions and returns a fn that is the composition of those fns. The returned fn takes a variable number of arguments, and returns the result of applying each fn to the result of applying the previous fn to the arguments (right-to-left).
(funcall (-compose 'square '+) 2 3) ;; => (square (+ 2 3))
(funcall (-compose 'identity 'square) 3) ;; => (square 3)
(funcall (-compose 'square 'identity) 3) ;; => (square 3)
Changes an n-arity function fn
to a 1-arity function that
expects a list with n items as arguments
(-map (-applify '+) '((1 1 1) (1 2 3) (5 5 5))) ;; => '(3 6 15)
(-map (-applify (lambda (a b c) `(,a (,b (,c))))) '((1 1 1) (1 2 3) (5 5 5))) ;; => '((1 (1 (1))) (1 (2 (3))) (5 (5 (5))))
(funcall (-applify '<) '(3 6)) ;; => t
Return a function of two arguments that first applies
transformer
to each of them and then applies operator
on the
results (in the same order).
In types: (b -> b -> c) -> (a -> b) -> a -> a -> c
(-sort (-on '< 'length) '((1 2 3) (1) (1 2))) ;; => '((1) (1 2) (1 2 3))
(-min-by (-on '> 'length) '((1 2 3) (4) (1 2))) ;; => '(4)
(-min-by (-on 'string-lessp 'number-to-string) '(2 100 22)) ;; => 22
Swap the order of arguments for binary function func
.
In types: (a -> b -> c) -> b -> a -> c
(funcall (-flip '<) 2 1) ;; => t
(funcall (-flip '-) 3 8) ;; => 5
(-sort (-flip '<) '(4 3 6 1)) ;; => '(6 4 3 1)
Return a function that returns c
ignoring any additional arguments.
In types: a -> b -> a
(funcall (-const 2) 1 3 "foo") ;; => 2
(-map (-const 1) '("a" "b" "c" "d")) ;; => '(1 1 1 1)
(-sum (-map (-const 1) '("a" "b" "c" "d"))) ;; => 4
Take n-ary function and n arguments and specialize some of them. Arguments denoted by <> will be left unspecialized.
See srfi-26
for detailed description.
(funcall (-cut list 1 <> 3 <> 5) 2 4) ;; => '(1 2 3 4 5)
(-map (-cut funcall <> 5) `(1+ 1- ,(lambda (x) (/ 1.0 x)))) ;; => '(6 4 0.2)
(-map (-cut <> 1 2 3) '(list vector string)) ;; => '((1 2 3) [1 2 3] "\^A\^B\^C")
Take a unary predicate pred
and return a unary predicate
that returns t if pred
returns nil and nil if pred
returns
non-nil.
(funcall (-not 'even?) 5) ;; => t
(-filter (-not (-partial '< 4)) '(1 2 3 4 5 6 7 8)) ;; => '(1 2 3 4)
Take list of unary predicates preds
and return a unary
predicate with argument x that returns non-nil if at least one of
the preds
returns non-nil on x.
In types: [a -> Bool] -> a -> Bool
(-filter (-orfn 'even? (-partial (-flip '<) 5)) '(1 2 3 4 5 6 7 8 9 10)) ;; => '(1 2 3 4 6 8 10)
(funcall (-orfn 'stringp 'even?) "foo") ;; => t
Take list of unary predicates preds
and return a unary
predicate with argument x that returns non-nil if all of the
preds
returns non-nil on x.
In types: [a -> Bool] -> a -> Bool
(funcall (-andfn (-cut < <> 10) 'even?) 6) ;; => t
(funcall (-andfn (-cut < <> 10) 'even?) 12) ;; => nil
(-filter (-andfn (-not 'even?) (-cut >= 5 <>)) '(1 2 3 4 5 6 7 8 9 10)) ;; => '(1 3 5)
Return a function fn
composed n
times with itself.
fn
is a unary function. If you need to use a function of higher
arity, use -applify
first to turn it into a unary function.
With n = 0, this acts as identity function.
In types: (a -> a) -> Int -> a -> a.
This function satisfies the following law:
(funcall (-iteratefn fn n) init) = (-last-item (-iterate fn init (1+ n))).
(funcall (-iteratefn (lambda (x) (* x x)) 3) 2) ;; => 256
(funcall (-iteratefn '1+ 3) 1) ;; => 4
(funcall (-iteratefn 'cdr 3) '(1 2 3 4 5)) ;; => '(4 5)
Return a function that computes the (least) fixpoint of fn
.
fn
must be a unary function. The returned lambda takes a single
argument, x
, the initial value for the fixpoint iteration. The
iteration halts when either of the following conditions is satisfied:
-
Iteration converges to the fixpoint, with equality being tested using
equal-test
. Ifequal-test
is not specified,equal
is used. For functions over the floating point numbers, it may be necessary to provide an appropriate approximate comparison test. -
halt-test
returns a non-nil value.halt-test
defaults to a simple counter that returns t after-fixfn-max-iterations
, to guard against infinite iteration. Otherwise,halt-test
must be a function that accepts a single argument, the current value ofx
, and returns non-nil as long as iteration should continue. In this way, a more sophisticated convergence test may be supplied by the caller.
The return value of the lambda is either the fixpoint or, if
iteration halted before converging, a cons with car halted
and
cdr the final output from halt-test
.
In types: (a -> a) -> a -> a.
(funcall (-fixfn 'cos 'approx-equal) 0.7) ;; ~> 0.7390851332151607
(funcall (-fixfn (lambda (x) (expt (+ x 10) 0.25))) 2.0) ;; => 1.8555845286409378
(funcall (-fixfn 'sin 'approx-equal) 0.1) ;; => '(halted . t)
Take a list of n functions and return a function that takes a list of length n, applying i-th function to i-th element of the input list. Returns a list of length n.
In types (for n=2): ((a -> b), (c -> d)) -> (a, c) -> (b, d)
This function satisfies the following laws:
(-compose (-prodfn f g ...) (-prodfn f' g' ...)) = (-prodfn (-compose f f') (-compose g g') ...)
(-prodfn f g ...) = (-juxt (-compose f (-partial 'nth 0)) (-compose g (-partial 'nth 1)) ...)
(-compose (-prodfn f g ...) (-juxt f' g' ...)) = (-juxt (-compose f f') (-compose g g') ...)
(-compose (-partial 'nth n) (-prod f1 f2 ...)) = (-compose fn (-partial 'nth n))
(funcall (-prodfn '1+ '1- 'number-to-string) '(1 2 3)) ;; => '(2 1 "3")
(-map (-prodfn '1+ '1-) '((1 2) (3 4) (5 6) (7 8))) ;; => '((2 1) (4 3) (6 5) (8 7))
(apply '+ (funcall (-prodfn 'length 'string-to-number) '((1 2 3) "15"))) ;; => 18
Yes, please do. Pure functions in the list manipulation realm only,
please. There's a suite of examples/tests in dev/examples.el
, so
remember to add tests for your additions, or I might break them later.
You'll find the repo at:
https://github.com/magnars/dash.el
Run the tests with:
make check
Regenerate the docs with:
make docs
I highly recommend that you install these as a pre-commit hook, so that the tests are always running and the docs are always in sync:
cp dev/pre-commit.sh .git/hooks/pre-commit
Oh, and don't edit README.md
or dash.texi
directly; they are
auto-generated. Change readme-template.md
or dash-template.texi
instead, respectively.
To ensure that dash.el
can be distributed with GNU ELPA or Emacs, we
require that all contributors assign copyright to the Free Software
Foundation. For more on this, see (info "(emacs) Copyright Assignment")
.
- Sped up
-uniq
by using hash-tables when possible (@cireu, #305). - Fixed
-inits
to be non-destructive (@SwiftLawnGnome, #313). - Fixed indent rules for
-some->
and family (@wbolster, #321). - Added
-zip-lists
which always returns a list of proper lists, even for two input lists (see issue #135).
- Added
--doto
, anaphoric version of-doto
(#282). - Aliased
-cons-pair-p
to-cons-pair?
(#288). - Generalized
-rotate
for|N|
greater than the length of the list (@leungbk, #290). - Added a mechanism to extend destructuring with custom matchers (@yyoncho, #277).
This release brings new destructuring features, some new control flow functions and performance optimizations.
- Added
-setq
with destructuring binding support similar to the-let
family (#116). - Added smarter key destructuring in
-let
and friends where variables are auto-derived from keys (#111). - Allowed
-let
bindings without a source value form (#256). - Added
-each-r
and-each-r-while
(@doublep, #159). - Added
-common-suffix
(@basil-conto, #263). - Improved performance of folds (
-reduce
and friends) (@basil-conto, #264).
This release retired Emacs 23 support.
- Added Edebug support for threading macros (@Wilfred).
- Added
-unzip
. - Added support for
-first-item
and-last-item
as place forms. - Added
-powerset
and-permutations
(@holomorph). - Added
-as->
for threading a named variable (@zck). - Added
-partition-after-pred
,-partition-before-pred
,-partition-after-item
, and-partition-before-item
(@zck). - Fixed a bug in
-any-p
and friends testing fornull
on lists containingnil
(#239). - Fixed infinite loop bug in
-zip
and-interleave
when called with empty input. - Added
-second-item
through-fifth-item
as alternatives tonth
(@Wilfred). - Added
-tails
and-inits
. - Added
-running-sum
and-running-product
. - Added the
-reductions[-r][-from]
family of functions (like-reduce
but collecting intermediate results). - Added
-common-prefix
(@basil-conto).
-let
now supports&alist
destructuring.- Various performance improvements.
-zip
might change in a future release to always return a list of proper lists. Added-zip-pair
for users who explicitly want the old behavior.- Enabled lexical binding in
dash.el
for Emacs versions 24 or newer (#130). - Added
-select-column
and-select-columns
. - Fixed
-map-last
and--remove-last
to be non-destructive (#158). - Added
-each-indexed
and--each-indexed
. - Added
-take-last
and-drop-last
. - Added the
-doto
macro. -cut <>
is now treated as a function, consistent with SRFI 26 (#185).
- Added GNU ELPA support (Phillip Lord).
- Added
-some->
,-some->>
, and-some-->
macros (Cam Saul). -is-suffix?
is now non-destructive.- Faster hash table implementation for
-union
. - Improvements to docstrings and examples.
- Lots of clean up w.r.t. byte compilation, debug macros, and tests.
- Added
-let
destructuring to-if-let
and-when-let
(Fredrik Bergroth).
- Added
-let
,-let*
, and-lambda
with destructuring. - Added
-tree-seq
and-tree-map-nodes
. - Added
-non-nil
. - Added
-fix
. - Added
-fixfn
(dash-functional
version1.2
). - Added
-copy
(Wilfred Hughes).
- Added
-butlast
.
-zip
now supports more than two lists (Steve Lamb).- Added
-cycle
,-pad
,-annotate
, and-zip-fill
(Steve Lamb). - Added
-table
,-table-flat
(finite Cartesian product). - Added
-flatten-n
. -slice
now supports a "step" argument.- Added functional combinators
-iteratefn
and-prodfn
. - Added
-replace
,-splice
, and-splice-list
which generalize-replace-at
and-insert-at
. - Added
-compose
,-iteratefn
, and-prodfn
(dash-functional
version1.1
).
- Added
-is-prefix-p
,-is-suffix-p
, and-is-infix-p
(Matus Goljer). - Added
-iterate
and-unfold
(Matus Goljer). - Added
-split-on
and-split-when
(Matus Goljer). - Added
-find-last-index
(Matus Goljer). - Added
-list
(Johan Andersson).
- Added
-same-items?
(Johan Andersson). - Various bugfixes.
- Added
-snoc
(Matus Goljer). - Added
-replace-at
,-update-at
,-remove-at
, and-remove-at-indices
(Matus Goljer).
- Added tree operations (Matus Goljer).
- Made Font Lock optional.
- Added
-compose
(Christina Whyte).
- Added indexing operations (Matus Goljer).
- Split out
dash-functional.el
(Matus Goljer). - Added
-andfn
,-orfn
,-not
,-cut
,-const
,-flip
, and-on
(Matus Goljer). - Fixed
-min
,-max
,-min-by
, and-max-by
(Matus Goljer).
- Added
-first-item
and-last-item
(Wilfred Hughes).
- Added
-rotate
(Matus Goljer).
- Added
-min
,-max
,-min-by
, and-max-by
(Johan Andersson).
- Added
-sum
and-product
(Johan Andersson).
- Added
-sort
. - Added
-reduce-r
(Matus Goljer). - Added
-reduce-r-from
(Matus Goljer).
- Added
-partition-in-steps
. - Added
-partition-all-in-steps
.
- Added
-last
(Matus Goljer). - Added
-insert-at
(Emanuel Evans). - Added
-when-let
and-if-let
(Emanuel Evans). - Added
-when-let*
and-if-let*
(Emanuel Evans). - Various bugfixes.
- Matus Goljer contributed lots of features and functions.
- Takafumi Arakaki contributed
-group-by
. - tali713 is the author of
-applify
. - Víctor M. Valenzuela contributed
-repeat
. - Nic Ferrier contributed
-cons*
. - Wilfred Hughes contributed
-slice
,-first-item
, and-last-item
. - Emanuel Evans contributed
-if-let
,-when-let
, and-insert-at
. - Johan Andersson contributed
-sum
,-product
, and-same-items?
. - Christina Whyte contributed
-compose
. - Steve Lamb contributed
-cycle
,-pad
,-annotate
,-zip-fill
, and a variadic version of-zip
. - Fredrik Bergroth made the
-if-let
family use-let
destructuring and improved the script for generating documentation. - Mark Oteiza contributed the script to create an Info manual.
- Vasilij Schneidermann contributed
-some
. - William West made
-fixfn
more robust at handling floats. - Cam Saul contributed
-some->
,-some->>
, and-some-->
. - Basil L. Contovounesios contributed
-common-prefix
. - Paul Pogonyshev contributed
-each-r
and-each-r-while
.
Thanks!
New contributors are very welcome. See the
Contribute
section above.
Copyright (C) 2012-2021 Free Software Foundation, Inc.
Author: Magnar Sveen magnars@gmail.com
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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