rizo / ppx_rule

Compile-time rewrite rules for OCaml

Compile-time optimization rules

This syntax extension implements compile-time rewrite rules to offer a powerful and flexible way to optimise your programs.

Consider the following simple examples:

(* Helper functions *)

let sum x y = x + y
let hello who = "Hello, " ^ who

(* Rules *)

let%rule sum 2 2 = 5
let%rule hello "rule" = "rules rock!"
let%rule sqrt 100000000000.0 = 316227.766017

let replaced = (sum 2 2, hello "rule", sqrt 100000000000.0)
let computed = (sum 1 1, hello "world", sqrt 99.0)

The syntax processor will replace the known patterns during the compilation time.
After the application the resulting code will look like this:

let sum x y = x + y
let hello who = "Hello, " ^ who

let replaced = (5, "rules rock!", 316227.766017)
let computed = (sum 1 1, hello "world", sqrt 99.0)

Note that the rules disappear during the compliation, so no runtime overhead is added to the program.

For more examples see the tests directory and for build options run make help.

Known Limitations

• Parametric rules are not implemented yet.
• The visibility of the rules is limited to the module where they were declared.
• Recursive rules may have unexpected results.

Project Status

This project is still in development and at this point should be considered a proof of concept, please use with care.

This syntax extension was inspired by Rule pragma for Haskell.