mdx allows to execute code blocks inside markdown files.
There are (currently) two sub-commands, corresponding
to two modes of operations: pre-processing (ocaml-mdx pp)
and tests (ocaml-mdx test).
The pre-processor mode allows to mix documentation and code, and to practice "literate programming" using markdown and OCaml.
The test mode allows to ensure that shell scripts and OCaml fragments in the documentation always stays up-to-date.
mdx is released as a single binary (called ocaml-mdx) and
can be installed using opam:
$ opam install mdxocaml-mdx interprets shell scripts inside sh code blocks as cram-like tests. The
syntax is the following:
-
Lines beginning with a dollar sign and a space are commands and will be run in the shell.
-
Multi-lines commands end by
\and continue with two spaces and a>sign on the next line:```sh $ <line1> \ > <line2> \ > <line3> ``` -
Commands support the heredoc syntax (
<<):```sh $ cat <<EOF \ > hello\ > world\ > EOF hello world ``` -
Lines beginning without a dollar sign are considered command outputs.
-
Command outputs can contain ellipses:
.... These will match any possible outputs (on zero, one or multiple lines). -
Arbitrary padding with whitespace is supported, as long as it is consistent inside a code block.
Here is an example of a markdown file using shell scripts inside code blocks, with a padding of 3:
```sh
$ for i in `seq 1 10`
1
...
10
```
ocaml-mdx will also consider exit codes when the syntax [<exit code>]is used:
```sh
$ exit 1
[1]
```
Note that nothing will be displayed when the exit code is 0 (e.g. in case of success).
ocaml-mdx interprets OCaml fragments. It understands normal code fragments and
toplevel code fragments (starting with a # sign and optionally ending with
;;). Arbitrary whitespace padding is supported, at long as it stays
consistent within a code block.
Toplevel fragments interleave OCaml code and their corresponding outputs.
Here is an example of normal OCaml code:
```ocaml
print_endline "42"
```
Here is an examples of toplevel OCaml code:
```ocaml
# print_endline "42"
42
```
ocaml-mdx pp allows to transform a markdown file into a valid
OCaml file, which can be passed to OCaml using the -pp
option.
For instance, given the following file.md document:
```ocaml
# print_endline "42"
42
```
Can be compiled and executed using:
$ ocamlc -pp 'ocaml-mdx pp' -impl file.md -o file.exe
$ ./file.exe
42This can be automated using dune:
(rule
((targets (file.ml))
(deps (file.md))
(action (with-stdout-to ${@} (run ocaml-mdx pp ${<})))))
(executable ((name file)))
Cram tests can be executed and checked with ocaml-mdx test <file.md>.
```sh
$ for i in `seq 1 10`; do echo $i; done
1
...
10
```
If the output is not consistent with what is expected,
<file.md>.corrected is generated.
To execute OCaml code and toplevel fragments, uses ocaml-mdx test <file.md>.
```ocaml
# print_endline "42"
42
```
If the output is not consistent with what is expected
<file.md>.corrected is generated.
To test that the code blocks of file.md stay consistent, one can use
dune's diff? stanza:
(alias
(name runtest)
(deps (:test file.md))
(action (progn
(run ocaml-mdx test %{test})
(diff? %{test} %{test}.corrected))))
This allows to test the consistency of a markdown file using the normal dev workflow:
$ dune runtest
will display a diff of the output if something has changed. For instance:
$ dune runtest
------ file.md
++++++ file.md.corrected
File "file.md", line 23, characters 0-1:
|
|```sh
-| $ for i in `seq 1 3`; do echo $i; done
+| $ for i in `seq 1 4`; do echo $i; done
| 1
| 2
| 3
+| 4
|```
And the changes can then be accepted using:
$ dune promote
Non-deterministic Outputs
ocaml-mdx test supports non-deterministic outputs:
```sh non-deterministic=output
$ <command>
<output>
```
In that case, ppx test <file> will run the command but will not
generate <file>.corrected if the new output differs from the one
described in the file. Use ocaml-mdx test --non-deterministic <file> to come
back to the default behaviour.
Non-deterministic Commands
ocaml-mdx test supports non-deterministic commands:
```ocaml non-deterministic=command
# Random.int 10;;
- : int = 5
```
In that case, ocaml-mdx test <file> will not run the command. Use ocaml-mdx test --non-deterministic <file> to come back to the default behaviour.
Separate environments can be defined for blocks:
x holds the value 1 in the environment e1.
```ocaml env=e1
let x = 1;;
```
```ocaml env=e1
module M = struct let k = 42 let f x = x * k end;;
```
x holds the value 3 in the environment e2.
```ocaml env=e2
let x = 3;;
```
We can retrieve the value of x in environment e1:
```ocaml env=e1
# print_int x;;
1
- : unit = ()
# print_int M.k;;
42
- : unit = ()
# M.f;;
- : int -> int = <fun>
```
Blocks can be processed or ignored depending on the current version of OCaml.
For example to have a different outcome whether we are past OCaml 4.06:
```ocaml version<4.06
# let f x = x + 1
val f : int -> int = <fun>
# let f y =
y^"foo"
val f : bytes -> bytes = <fun>
```
```ocaml version>=4.06
# let f x = x + 1
val f : int -> int = <fun>
# let f y =
y^"foo"
val f : string -> string = <fun>
```
The available operators are <>, >=, >, <=, < and =.
The version number can be of the following forms:
*XX.YX.Y.Z
Environment variables can be declared at the beginning of a block:
```ocaml set-FOO=bar,set-BAR=foo
# print_endline (Sys.getenv "FOO")
bar
- : unit = ()
# print_endline (Sys.getenv "BAR")
foo
- : unit = ()
```
Those variables are then available in the subsequent blocks
```ocaml
# print_endline (Sys.getenv "FOO")
bar
- : unit = ()
```
It is possible to test or execute only a subset of the file using
sections using the --section option (short name is -s). For
instance ocaml-mdx pp -s foo will only consider the section matching the
perl regular expression foo.
ocaml-mdx can generate dune rules to synchronize .md files with .ml files.
Consider the test/dune_rules.md file that contains blocks referring to files dune_rules_1.ml and dune_rules_2.ml, running:
$ ocaml-mdx rule test/dune_rules.md
generates the following dune rules on the standard output:
(alias
(name runtest)
(deps (:x test/dune_rules.md)
(:y1 dune_rules_1.ml)
(:y0 dune_rules_2.ml)
(source_tree foo))
(action (progn
(run ocaml-mdx test --direction=infer-timestamp %{x})
(diff? %{x} %{x}.corrected)
(diff? %{y1} %{y1}.corrected)
(diff? %{y0} %{y0}.corrected))))