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_build | ||
*.byte | ||
*.native | ||
stdlib_ml/stdlib.cmi | ||
stdlib_ml/stdlib.cmo | ||
.ocamldebug | ||
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REC | ||
B _build | ||
PKG str | ||
PKG compiler-libs.common | ||
PKG ocaml-migrate-parsetree |
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# Js\_of\_ocaml bis ("The Generator") | ||
## Why bis? & Purpose | ||
Because, there is already a tool named `js_of_ocaml` whose job is | ||
to produce efficient Javascript from OCaml bytecode. We are not that tool. | ||
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Here, we try to translate OCaml syntax to 'simple' ECMAScript syntax, the | ||
purpose of it is to generate readable ECMAScript code, so that it | ||
could later be use in a step-by-step ECMAScript interpreter. | ||
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## Dependencies | ||
See parent directory. | ||
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## What is built | ||
* **main**: The main ml-to-js compiler. Can produce files in one of 5 modes, | ||
using the `-mode` parameter: | ||
* `log`: Executable JS output with logging function calls for use with the | ||
debugger. | ||
* `unlog`: Plain executable JS output | ||
* `token`: Produces `unlog` annotated with token identifiers for `log`. And | ||
produces an `.mlloc.js` file mapping token identifiers to locations of the | ||
input `.ml` source file. | ||
* `pseudo`: 'Pseudo'-js output. Makes use of monadic let bindings alike the | ||
input OCaml to improve readability. | ||
* `ptoken`: `token` equivalent for `pseudo` output files. | ||
* **lineof**: Converts and combines `.token.js`, `.ptoken.js`, and `.mlloc.js` | ||
files into `lineof.js` which maps token identifiers to file locations. | ||
* **assembly**: Linker for compiled `.log.js` files into a single executable | ||
`.js` file. | ||
* **displayed_sources**: Produces string versions of the relevant source | ||
files, for display. | ||
* **monad_ppx**: PPX rewriter for monadic binder extension syntax. See below. | ||
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Each of these programs may be compiled to a bytecode or native target as | ||
desired. Bytecode is the default. | ||
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### Makefile Targets | ||
The following `make` targets are defined: | ||
* `default`: Compiles bytecode versions of the programs and the stdlib. | ||
* `all`: Compiles bytecode and native versions of the programs and the stdlib. | ||
* `byte` / `native`: Compiles bytecode or native versions of the programs. | ||
* \*`.byte` / \*`.native`: Compiles the specified program into bytecode or | ||
native code. | ||
* `debug`: Compiles bytecode versions of the programs with debug symbols, and | ||
the appropriate `.ocamldebug` configuration file. | ||
* `test`: Compiles and executes the test suite. See below. | ||
* `clean`: Cleans built targets. | ||
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## How does it work? | ||
In order to get the statically typed abstract syntax tree (STAST) of OCaml we | ||
link against compiler-libs, we have tested against versions 4.04.0. Previous | ||
versions are available for >= 4.02.1. | ||
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On top, of this STAST, there is a custom back-end that compiles OCaml to | ||
ECMAScript. The code written in OCaml cannot rely on code from the typical | ||
standard library. Therefore a file named `stdlib.mli` (found in the directory | ||
`stdlib_ml`) contains all the required definitions for the examples to work. | ||
This file as a twin which is `stdlib.js`, in this file the functions whose | ||
prototype is in `stdlib.mli` are defined here. | ||
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## About the subset of OCaml supported | ||
* **Let** declarations, except `let () =`. Recursive declarations are | ||
supported. | ||
* **If then else** statements, as expected `if then else` expressions return a | ||
value. | ||
* **Pattern matching**, only one level of pattern matching over arbitrary | ||
types. | ||
* **Type declarations**, if a constructor take arguments (one or more), you | ||
should add an annotations to provide default names for the parameters. See | ||
example below. | ||
```ocaml | ||
type 'a tree = | Leaf of 'a [@f value] | Node of 'a | ||
tree * 'a * 'a tree [@f left, value, right] | ||
``` | ||
* **Records** Records are translated to objects. Record copying using the | ||
OCaml `with` syntax is supported for any number of field updates. | ||
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## About the Subset of JavaScript Used | ||
* Object.assign (ES6) | ||
* No type casting | ||
* No prototypes | ||
* Arrays (for tuples) | ||
* Switch on strings (used for type constructor matching) | ||
* `with` as a simplistic means of linking module definitions. | ||
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## About the Monadic Rewriter PPX | ||
This is a OCaml AST preprocessor that converts `let%x` syntax into the | ||
monadic binder `if_x` with the continuation as the bound expression of the | ||
let term. | ||
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For example: | ||
* `let%some x = expr in cont` ↝ `if_some expr (fun x -> cont)` | ||
* `let%spec (s,x) = expr in cont` ↝ `if_spec expr (fun s x -> cont)` | ||
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The full list of available monads is provided in the file | ||
[`monadic_binder_list.ml`](./monadic_binder_list.ml). This file should be | ||
configured as appropriate for the target application. The current | ||
configuration is for jsref. | ||
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## Test Suite | ||
The `tests` directory contains test files for the generator to compile. Test | ||
cases will first be built and run with the standard OCaml compiler to check | ||
that the assertions made within the tests are correct. The tests are then | ||
compiled with the generator and executed with Nodejs to ensure that the | ||
compiled versions are also correct. Cross-checking of results is not | ||
performed, it is expected that all tests should pass under both execution | ||
environments. | ||
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The test case library interface is described in | ||
(tests/lib/mocha.mli)[./tests/lib/mocha.mli], it is designed to be similar in | ||
style to the Mocha JS testing framework. The JS test environment is backed | ||
directly by Mocha, the OCaml test environment is Alcotest with a wrapper to | ||
provide a Mocha interface. | ||
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Tests are built and executed using the `make test` command in this directory. | ||
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## Other Notes | ||
Historical versions of the repository required the OCaml 4.02.1 compiler | ||
source code to compile directly against. We are unable to redistribute | ||
these files for licensing reasons. If for some reason you want to build a | ||
historic version, then drop the parsing, typing and utils directories from | ||
the OCaml distribution into this directory, some further configuration may | ||
be required... The whole historic distribution archived in the private | ||
jscert\_dev repository. |
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