hoogle VS merlin

For what it's worth, I've never used/heard of this function myself, but I used the awesome https://hoogle.haskell.org site and searched by the type signature:

Looks cool.

Maybe it can also search by signature like https://hoogle.haskell.org/ - would be a killer feature for me, but niche :)

As for finding things in those many modules, I usually check hoogle first: https://hoogle.haskell.org/

If the type doesn't make it clear, then I read the docs or source on hackage. To find the right hackage package, I generally use hoogle which can be queried by name or by type!

Cool project and overall I'd say your good is good. There's some stylistic things I might change. Below I've commented on a bunch of random stuff just to give you food for thought and possible leads to look into as a continuing to learn haskell sort of thing. I was pretty bad about citing where functions are from, so I recommend using something like hoogle (https://hoogle.haskell.org/) if it's not clear what function I meant.

Fun fact: Hoogle is actually a thing: https://hoogle.haskell.org

You can search for a type signature on Hoogle. For example, if I wanted to know if there's a function from lists to Maybe I could search for [a] -> Maybe [a]

Haskell has a search engine, called hoogle, for looking up types and functions. It's invaluable for getting familliar with the language. https://hoogle.haskell.org

hoogle

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.

Assuming you followed the instructions you got when you installed merlin (shows up as part of opam's output), you either need a manually created .merlin file to tell it where to find things, or a dune file that lists dependencies with which merlin can auto-create its own. Preferably the latter: use dune and let merlin do the rest.

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.