Notes for myself on how to stay consistent
Incantation at the top of each file:
{-# LANGUAGE MultiWayIf
, PatternGuards
, PatternSynonyms
#-}Haskell gives a lot of ways to write the same definition.
-- clunky
foldr f z (x : xs) = x `f` foldr f z xs
foldr _ z _ = z
foldr f z xs = case xs of
x : xs' -> x `f` foldr f z xs'
_ -> z
foldr f z = loop
where
loop (x : xs) = x `f` loop xs
loop _ = z
loop xs = case xs of
x : xs' -> x `f` loop xs
_ -> z
-- LambdaCase
loop = \case
x : xs -> x `f` loop xs
_ -> z
-- PatternGuards (Haskell2010)
loop xs
| x : xs' <- xs -> x `f` loop xs'
| otherwise -> z
-- PatternGuards and MultiWayIf
loop xs = if
| x : xs' <- xs -> x `f` loop xs'
| otherwise -> z
Sometimes combining MultiWayIf with PatternGuards can lead to a more consistent style. Sometimes it can be ugly. Below are some examples where it's locally equivalent or worse.
if b
then y
else z
-- vs
if
| b -> y
| otherwise -> z
case f x of y -> z
-- vs
if | y <- f x -> z
foo x
| p x = y
| otherwise = z
-- vs
foo x = if
| p x -> y
| otherwise -> z
foo x
| P y <- f x
= y
-- vs
foo x = if
| p y <- f x
-> y
case f x of
C x
| p x -> x
| q x -> y
z -> v
-- vs (alas)
let u = f x in if
| C x <- u
-> if
| p x -> x
| q x -> y
| z <- u
-> v
\case
y -> v
z -> u
-- vs (alas)
\ x -> if
| y <- x -> v
| z <- x -> u
-- or
\ x -> if
| y <- x
-> v
| z <- x
-> u