Feature Request: Collapsing Indirection

[anchpop]

"Collapsing indirection" is a feature which I suspect is difficult to implement. I expect most people here are familiar with it from that one talk, but just in case I'll recap it here.

Imagine this is your project:

-- some distant file
addone x = x + 1
-- file you're working on now
addonethendouble x = (addone x) * 2

You're looking at addonethendouble and wondering what exactly addone x is doing. You right-click addone and select collapse indirection in your IDE. Suddenly, that line changes to look like this:

addonethendouble x = (x + 1) * 2

The x+1 section probably should not be editable, but that seems like an issue for the IDE and not for HIE.

In theory, you should be able to use "collapse indirection" repeatedly, drilling down as far as you need to in order to understand the code.

This raises design questions. How to handle pointfree style vs pointful functions, functions defined as lambdas, functions using where, functions using pattern matching, functions not passed to all their arguments, occasions when it's not obvious which function to collapse to (e.g. pure 3) due to typeclasses, and I'm sure many others. It's not obvious to me how to address these.

I'm not very experienced with HIE, but I would be more than happy to help to contribute this feature, since I think it would be massively helpful to understanding a codebase and for beginners to familiarize themselves with common functions. But, I would probably need some guidance or a nudge in the right direction.

[lukel97]

I don't see any APIs inside the LSP specification that we can use to directly show the expansion inline, but VS code definitely has a peek/preview API that could work for this.
HIE has a plugin system where we can expose custom commands though, so I think you could expose a command to return the expansion and then handle using the peek feature in the VS code plugin.
As for the GHC stuff itself: You'll probably want to do this inside GhcMod.hs.
Here you'll be able to create a custom command (I think the case-splitting command is a good example) which will have access to a TypecheckedModule, which you can use the GHC library to pick apart the AST and do the necessary magic.
Hopefully this will help give you an idea of where to start looking!

[anchpop]

cool! I'll try to get started hacking on this soon

…

On Fri, Jan 25, 2019, 7:09 PM Luke Lau ***@***.***> wrote: I don't see any APIs inside the LSP specification <https://microsoft.github.io/language-server-protocol/specification#version_3_14_0> that we can use to directly show the expansion inline, but VS code definitely has a peek/preview API that could work for this. HIE has a plugin system where we can expose custom commands though, so I think you could expose a command to return the expansion and then handle using the peek feature in the VS code plugin <https://github.com/alanz/vscode-hie-server>. As for the GHC stuff itself: You'll probably want to do this inside GhcMod.hs <https://github.com/haskell/haskell-ide-engine/blob/master/src/Haskell/Ide/Engine/Plugin/GhcMod.hs> . Here you'll be able to create a custom command (I think the case-splitting command is a good example) which will have access to a TypecheckedModule, which you can use the GHC library <http://hackage.haskell.org/package/ghc> to pick apart the AST and do the necessary magic. Hopefully this will help give you an idea of where to start looking! — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#1062 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADigR98GEeya7BjEtEkOpUuhDBKr2mZcks5vG5zEgaJpZM4aPYDm> .