SimFormat

Formats Haskell import lists.

It produces import lists that look like this:

import Range.Shared.Types
  ( ExternalRef(..), Imports(Imports), SomeExternalRef(SomeExternalRef), SpecEntity(..)
  , SpecRef(SpecRefExternal, SpecRefLocal), ExternalEntities, IsSpecEntity, ResolvedSpec
  , SpecEntities, VmRepetitionGroup, VmRgTag, importsConfigModuleDefs, importsOperatingSystems
  , importsVmTemplates, specEntitiesConfigModuleDefs, specEntitiesOperatingSystems
  , specEntitiesVmTemplates, specEntity, specificationEntities
  )

Usage

By default, simformat formats an entire git repository using a .simformatrc config file in the repo root to identify files to include. To bypass this behavior you can call it with simformat <file> which will format the file regardless of whether it's in the configuration. It should always succeed: if it cannot find any import blocks, it will simply pass the text on unchanged. You can always run simformat --help for more command-line options.

$ stack install

Emacs

From within Emacs, assuming you have the haskell-mode and stylish-haskell packages installed and working, (setq haskell-mode-stylish-haskell-path "simformat -e") and (setq haskell-stylish-on-save t) should automatically reformat your import list on every save.

If you prefer not to run code on save, you can use shell-command-on-region with a region active and the prefix argument set, i.e. C-u M-| simformat

Vim

If you use null-ls.nvim an excellent plugin for integrating external tools for formatting / diagnostics in a way compatible with neovim's builtin LSP you can use this snippet to register a source that will format Haskell files using simformat:

lua << EOF
local null_ls = require('null-ls')
local simformat = {
  name = 'simformat',
  method = null_ls.methods.FORMATTING,
  filetypes = {'haskell'},
  generator = require('null-ls.helpers').formatter_factory {
    command = 'simformat',
    args = {'-e'},
    to_stdin = true,
  },
}
null_ls.register(simformat)
EOF

One possible vim solution is to add this to your .vimrc file:

function! s:RunSimformat()
  if &filetype == 'haskell'
    let cmd = 'simformat -e'
    let stdin = join(getline(1, '$'), "\n")
    let output = system(cmd, stdin)
    if v:shell_error != 0
      echom output
    else
      call s:OverwriteBuffer(output)
    endif
  endif
endfunction

function! s:OverwriteBuffer(output)
  if &modifiable
    let l:curw=winsaveview()
    try | silent undojoin | catch | endtry
    let splitted = split(a:output, '\n')
    if line('$') > len(splitted)
      execute len(splitted) .',$delete'
    endif
    call setline(1, splitted)
    call winrestview(l:curw)
  else
    echom "Cannot write to non-modifiable buffer"
  endif
endfunction

augroup Simformat
  autocmd!
  autocmd BufWritePre * call <SID>RunSimformat()
augroup END

To format without running on save, run :!simformat (to format all files that are children of the pwd) or run :%!simformat -e (to format just the current file).

VSCode

Add this to ~/Library/Application Support/Code/User/settings.json once you have installed the Run on Save extension.

    "runOnSave.statusMessageTimeout": 3000,
    "runOnSave.commands": [
        {
            "match": ".*\\.hs$",
            "notMatch": "[\\\\\\/]_[^\\\\\\/]*\\.hs$",
            "command": "simformat ${file}",
            "runIn": "backend",
            "runningStatusMessage": "Formatting ${fileBasename}",
            "finishStatusMessage": "${fileBasename} formatted"
        }
    ]

.simformatrc example

The config file, .simformatrc, is expected to live in the directory where the simformat executable is being run. It's a YAML file containing two keys: files and whitelist, each with a list of filepaths. If .simformatrc is not present, it will interpret files to be all files, and whitelist to be empty.

files:
  - foo
whitelist:
  - foo/bar