Wingman plugin for Haskell Language Server.

Please see the README on GitHub at https://github.com/haskell/haskell-language-server#readme

Wingman for Haskell

"Focus on the important stuff; delegate the rest"

Dedication

There's a lot of automation that can happen that isn't a replacement of humans, but of mind-numbing behavior.

--Stewart Butterfield

Overview

Wingman writes the boring, auxiliary code, so you don't have to. Generate functions from type signatures, and intelligently complete holes.

Getting Started

Wingman for Haskell is enabled by default in all official release of Haskell Language Server. Just hover over a typed hole, run the "Attempt to fill hole" code action, et voila!

Usage

When enabled, Wingman for Haskell will remove HLS support for hole-fit code actions. These code actions are provided by GHC and make typechecking extremely slow in the presence of typed holes. Because Wingman relies so heavily on typed holes, these features are in great tension.

The solution: we just remove the hole-fit actions. If you'd prefer to use these actions, you can get them back by compiling HLS without the Wingman plugin.

Editor Configuration

Enabling Jump to Hole

Set the haskell.plugin.tactics.config.hole_severity config option to 4, or hint if your editor uses a GUI for its configuration. This has the potential to negatively impact performance --- please holler if you notice any appreciable slowdown by enabling this option.

coc.nvim

The following vimscript maps Wingman code-actions to your leader key:

" use [h and ]h to navigate between holes
nnoremap <silent> [h :<C-U>call CocActionAsync('diagnosticPrevious', 'hint')<CR>
nnoremap <silent> ]h :<C-U>call <SID>JumpToNextHole()<CR>

" <leader>d to perform a pattern match, <leader>n to fill a hole
nnoremap <silent> <leader>d  :<C-u>set operatorfunc=<SID>WingmanDestruct<CR>g@l
nnoremap <silent> <leader>n  :<C-u>set operatorfunc=<SID>WingmanFillHole<CR>g@l
nnoremap <silent> <leader>r  :<C-u>set operatorfunc=<SID>WingmanRefine<CR>g@l
nnoremap <silent> <leader>c  :<C-u>set operatorfunc=<SID>WingmanUseCtor<CR>g@l
nnoremap <silent> <leader>a  :<C-u>set operatorfunc=<SID>WingmanDestructAll<CR>g@l


function! s:JumpToNextHole()
  call CocActionAsync('diagnosticNext', 'hint')
endfunction

function! s:GotoNextHole()
  " wait for the hole diagnostics to reload
  sleep 500m
  " and then jump to the next hole
  normal 0
  call <SID>JumpToNextHole()
endfunction

function! s:WingmanRefine(type)
  call CocAction('codeAction', a:type, ['refactor.wingman.refine'])
  call <SID>GotoNextHole()
endfunction

function! s:WingmanDestruct(type)
  call CocAction('codeAction', a:type, ['refactor.wingman.caseSplit'])
  call <SID>GotoNextHole()
endfunction

function! s:WingmanDestructAll(type)
  call CocAction('codeAction', a:type, ['refactor.wingman.splitFuncArgs'])
  call <SID>GotoNextHole()
endfunction

function! s:WingmanFillHole(type)
  call CocAction('codeAction', a:type, ['refactor.wingman.fillHole'])
  call <SID>GotoNextHole()
endfunction

function! s:WingmanUseCtor(type)
  call CocAction('codeAction', a:type, ['refactor.wingman.useConstructor'])
  call <SID>GotoNextHole()
endfunction

Emacs

When using Emacs, wingman actions should be available out-of-the-box and show up e.g. when using M-x helm-lsp-code-actions RET provided by helm-lsp or as popups via lsp-ui-sideline.

Additionally, if you want to bind wingman actions directly to specific keybindings or use them from Emacs Lisp, you can do so like this:

;; will define elisp functions for the given lsp code actions, prefixing the
;; given function names with "lsp"
(lsp-make-interactive-code-action wingman-fill-hole "refactor.wingman.fillHole")
(lsp-make-interactive-code-action wingman-case-split "refactor.wingman.caseSplit")
(lsp-make-interactive-code-action wingman-refine "refactor.wingman.refine")
(lsp-make-interactive-code-action wingman-split-func-args "refactor.wingman.spltFuncArgs")
(lsp-make-interactive-code-action wingman-use-constructor "refactor.wingman.useConstructor")

;; example key bindings
(define-key haskell-mode-map (kbd "C-c d") #'lsp-wingman-case-split)
(define-key haskell-mode-map (kbd "C-c n") #'lsp-wingman-fill-hole)
(define-key haskell-mode-map (kbd "C-c r") #'lsp-wingman-refine)
(define-key haskell-mode-map (kbd "C-c c") #'lsp-wingman-use-constructor)
(define-key haskell-mode-map (kbd "C-c a") #'lsp-wingman-split-func-args)

Other Editors

Please open a PR if you have a working configuration!

Features

• Type-directed code synthesis, including pattern matching and recursion
• Automatic case-splitting --- just run the "Case split on <x>" code action
• Smart next actions, for those times it can't read your mind

Support

Please consider pledging on Patreon to support the project and get access to cutting-edge features.