bisect_ppx VS merlin

It's not so clear to me what you want, the following come to mind: - if you want to "inspect the recursive calls" of a recursive function, you may not need any instrumentation: you can turn your function in open-recursion style, and provide a fixpoint combinator that does the inspection (see code below) - if you want to instrument the code globally, one easier-than-most approach is to use a ppx preprocessor to instrument the code (this assumes that the logic you want can be expressed as a slight modification of the user-written code), see ppx_bisect (code-coverage instrumentation) for example.

Merlin: Context sensitive completion for OCaml in Vim and Emacs\ (0 comments)

Instead of searching functions based on their type structure (like Hoogle), you could search for functions that "consume"/"produce" values of given types (like OCaml's Merlin). I think Rust already computes variance of type constructors, so such a tool just would have to obtain this information.

However, after posting this question I stumbled upon this Github issue where they say it isn't supposed to work out of the box and you're supposed to bind a key to it by editing your .emacs file. Turns out the default .emacs file binds auto-complete to "backtab" which means Shift+Tab but that didn't work. I did eventually discover that I can get some kind of completion by binding backtab to completion-at-point like this:

Self-advertising: I partcipated to the writing of Merlin: A Language Server for OCaml (Experience Report), which explains the overall design of Merlin, a language server for OCaml. A key idea of Merlin are that classic lexing-parsing-typing pipelines can easily be adapted to be incremental for a Language Server, especially when they are using immutable data structures.