ReScript Syntax

Documentation: https://rescript-lang.org/docs/manual/latest/overview

This repo is the source of truth for the ReScript parser & printer. Issues go here.

You don't need this repo to use the ReScript syntax. This comes with ReScript >=8.1. This repo is for syntax developers.

Contribute

Why

A detailed discussion by Jonathan Blow and Casey Muratori on why you would hand-roll a parser for a production quality programming language Discussion: Making Programming Language Parsers, etc

"One reason why I switched off these parser tools is that the promises didn't really materialize. The amount of work that I had to do change a yacc script from one language to a variant of that language was more than if I hand wrote the code myself. " J. Blow.

Setup & Usage (For Repo Devs Only)

Required:

• OCaml 4.10 or later
• Dune
• Reanalyze
• OS: macOS, Linux or Windows

git clone https://github.com/rescript-lang/syntax.git
cd syntax
opam install . --deps-only --with-test
make # or "dune build"

This will produce the three binaries rescript, tests and bench (with .exe extension on Windows).

We only build production binaries, even in dev mode. No need for a separate dev binary when the build is fast enough. Plus, this encourages proper benchmarking of the (production) binary each diff.

After you make a change:

make

Run the core tests:

make test

Run the extended tests (not fully working on Windows yet):

make roundtrip-test

Those will tell you whether you've got a test output difference. If it's intentional, check them in.

Debug a file:

# write code in test.res
dune exec -- rescript test.res # test printer
dune exec -- rescript -print ast test.res # print ast
dune exec -- rescript -print comments test.res # print comment table
dune exec -- rescript -print ml test.res # show ocaml code
dune exec -- rescript -print res -width 80 test.res # test printer and change default print width

Benchmark:

make bench

Enable stack trace:

# Before you run the binary
export OCAMLRUNPARAM="b"

This is likely a known knowledge: add the above line into your shell rc file so that every shell startup you have OCaml stack trace enabled.

Development Docs

Folder Structure

• src contains all the parser/printer source code. Don't change folder structure without notice; The rescript-compiler repo uses this repo as a submodule and assumes src.
• benchmarks, cli and tests contain the source code for the executables used for testing/benchmarking. These are not used by the rescript-compiler repo.

Error Reporting Logic

Right now, ReScript's compiler's error reporting mechanism, for architectural reasons, is independent from this syntax repo's error reporting mechanism. However, we do want a unified look when they report the errors in the terminal. This is currently achieved by (carefully...) duplicating the error report logic from the compiler repo to here (or vice-versa; either way, just keep them in sync). The files to sync are the compiler repo's super_location.ml and super_code_frame.ml, into this repo's res_diagnostics_printing_utils.ml. A few notes:

• Some lines are lightly changed to fit this repo's needs; they're documented in the latter file.
• Please keep these files lightweight and as dependency-less as possible, for easier syncing.
• The syntax logic currently doesn't have warnings, only errors, and potentially more than one.
• In the future, ideally, the error reporting logic would also be unified with GenType and Reanalyze's. It'd be painful to copy paste around all this reporting logic.
• The errors are reported by the parser here.
• Our editor plugin parses the error report from the compiler and from the syntax here.

Example API usage

let filename = "foo.res"
let src = FS.readFile filename

let p =
  (* intended for ocaml compiler *)
  let mode = Res_parser.ParseForTypeChecker in
  (* if you want to target the printer use: let mode = Res_parser.Default in*)
  Res_parser.make ~mode src filename

let structure = Res_core.parseImplementation p
let signature = Res_core.parseSpecification p

let () = match p.diagnostics with
| [] -> () (* no problems *)
| diagnostics -> (* parser contains problems *)
  Res_diagnostics.printReport diagnostics src