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General

• ModuleName.(e) is equivalent to let open ModuleName in e
  • The module ModuleName is opened only for e
  • https://stackoverflow.com/questions/30493644/ocaml-operator
• Style guide
  • http://ocamlverse.net/content/documentation_guidelines.html
  • Jane street style guide is aligned with their libraries: https://opensource.janestreet.com/standards/

[@tailcall]

• Ocaml compiler does tail optimization by default.
• Use of [@tailcall] on a function will induce error if the function cannot be made tail recursive.
• It only checks if the call is in tail position. Not the whole function.

Error will be like this:

Error (warning 51 [wrong-tailcall-expectation]): expected tailcall

Line number directives

• Starts with a #
• These are not comments. But are ignored by ocaml lexer ??
• https://ocaml.org/manual/5.3/lex.html#sss:lex-linedir

Import only some names from a module

Unlike Haskell, no such facility is available.

But this should be good enough:

let value1, value2 = ModuleName.(value1, value2) 

https://stackoverflow.com/questions/38937520/ocaml-open-only-certain-values-types-from-module

Emacs: tuareg mode

Can work with utop.

• M-x run-ocaml: start tuareg (is an alias for tuareg-run-ocaml)
• C-c C-s: Start utop
• C-x C-e / C-c C-e: Feed block of current line (or selection) to utop
• C-c C-t: Show type of value under cursor

https://ocamlpro.github.io/ocaml-cheat-sheets/tuareg-mode.pdf

---

Tuareg: Emacs major mode for OCaml.

• Start: ??
• Eval phrase: C-x C-e or C-c C-e
• Eval buffer: C-c C-b
• Eval region: C-c C-r
• Compile: C-c C-c
• Show type of identifier (needs annotation file): C-c C-l
• Indent: C-c C-q

Insert template code snippet:

• C-c . l: let _ in
• C-c . i: if _ then _ else _
• C-c . m: match _ with _

ocamlformat

An automatic code formatter.

dune integration (needs setup in dune-project):

• Dry run: dune build @fmt

• Apply: dune promote

• https://dune.readthedocs.io/en/stable/howto/formatting.html

• Ignore all warnings: dune <command> --profile release

  • By default, warnings are treated like errors
  • https://discuss.ocaml.org/t/disable-make-all-warnings-errors/11658

utop

• Next completion: M-right
• Previous completion: M-left
• Select completion: M-Tab
• Load a file: #use "myfile.ml"

https://www.systutorials.com/utop-key-bindings-key-shortcuts/

ppx

• Preprocessors. Change the program before giving it to compiler.
• Similar to C macros??

Links:

• https://ocaml.org/docs/metaprogramming
• https://github.com/ocaml-ppx/ppxlib/blob/main/examples/simple-extension-rewriter
• http://ocamlverse.net/content/metaprogramming.html
• https://tarides.com/blog/2019-05-09-an-introduction-to-ocaml-ppx-ecosystem/

Eg:

• ppx_{derivingjsonschema}: JSON schema from ocaml type
• ppx_yojsonconv: JSON de/serialization

[@@deriving _]

• To provide functionality similiar to automatic typeclass derivation in haskell.
• Needs third-party libraries.
  • https://github.com/ocaml-ppx/ppxlib
  • https://github.com/ocaml-ppx/ppx_deriving (old)

odoc

https://ocaml.github.io/odoc/

• Meant to supercede an older tool?: ocamldoc

  • https://v2.ocaml.org/manual/ocamldoc.html

• Cross referencing possible

• Use comments in the (** ‥ *) format.

• Module docstring: First odoc comment

• Type, exception docstrings: odoc comment right before definition (normal comments can be there in between though)

• Constructor docstring: On same line

• Function docstring: before and after function definition

• Stop odoc mode with a 'stop comment': (**/**)

  • Another stop comment will re-enable odoc

• Inlince code: [hello]

List: ul, ol

String formatting

• {b hello}: bold
• {i hello}: italic
• {e hello}: emphasize

Alignment:

• {L hello}: left
• {C hello}: centre
• {R hello}: right