ocamlmig is a command line tool for rewriting ocaml source code with access to scope and type information.

As a simple example of what it can do, let's say an opam-installed library A provides this interface:

val new_name : int -> int

val old_name : int -> int
[@@migrate { repl = Rel.new_name }]

and your repository contains a file b.ml:

let _ = A.old_name 1

then you could do:

$ git diff b.ml
$ ocamlmig migrate -w
$ git diff b.ml
-let _ = A.old_name 1
+let _ = A.new_name 1

Examples of real rewrites:

• Renaming operators (not trivial because the operators change precedence)
• Switching code using both Stdlib and Core to mostly Core

If that piqued your interest, you can find more information about what ocamlmig does, and using it.

This is work in progress, so many things are only partially implemented, but the existing functionality as is should still be interesting.