While I can't speak specifically to ReasonML, I have used Ocaml and Typescript extensively in https://www.jeroo.org/beta.
I used Ocaml to write the a (simple) custom compiler framework, which gave me the benefits of better type safety than Typescript.
Typescript was used with Angular to create everything else (the custom-bytecode interpreter and user-interface. Typescript gives me the advantage of good interop with Javascript libraries, mainly CodeMirror for the editor.
The interop with Ocaml and Typescript was pretty good. I just exported the Ocaml as a Javascript module using Js-of-ocaml with one exported function that starts off the compilation. Then it returns a list of a custom instruction object, which acts as a 5-tuple with all of the instruction fields.
I used Ocaml to write the a (simple) custom compiler framework, which gave me the benefits of better type safety than Typescript.
Typescript was used with Angular to create everything else (the custom-bytecode interpreter and user-interface. Typescript gives me the advantage of good interop with Javascript libraries, mainly CodeMirror for the editor.
The interop with Ocaml and Typescript was pretty good. I just exported the Ocaml as a Javascript module using Js-of-ocaml with one exported function that starts off the compilation. Then it returns a list of a custom instruction object, which acts as a 5-tuple with all of the instruction fields.