What is neco-ghc-lushtags?

neco-ghc-lushtags is a blazing fast completion plugin for Haskell using ghc-mod, lushtags, and ghc-mod-cache.

neco-ghc-lushtags is a project forked from neco-ghc, so most of the functions are derived from neco-ghc. If you have not used neco-ghc before, please see the site first.

Anyway, this plugin completes words in the following way:

• pragma
• language
• importing a module
• importing a function of a module
• function based on importing modules
• record accessors
• non-standard (local) modules

neco-ghc-lushtags achieves faster completion using ghc-mod-cache, which is developed in this project. I had been frustrated by slow ghc-mod. neco-ghc calls ghc-mod so often, each of which calls may take a few seconds but they often blocked vim for more than ten seconds, which was unacceptable for me. I noticed that results of ghc-mod could be cached in most cases, so I developed ghc-mod-cache, which is a simple wrapper script of ghc-mod. ghc-mod-cache caches the result of ghc-mod browse. neco-ghc-lushtags can response in less than a second after the result of ghc-mod is cached.

Another source of frustration was that neco-ghc does not complete functions in modules not installed. Let me show an example. Suppose we are working on a scaffolded Yesod site. neco-ghc does not complete functions in non-standard modules such as Foundation, Import, etc. neco-ghc-lushtags can completes such functions.

neco-ghc was originally implemented by @eagletmt on July 25, 2010, and then ujihisa added some new features. neco-ghc-lushtags was forked from neco-ghc by @mkasa on May 31, 2015.

Install

• Install stack.
• Install ghc-mod package by stack install ghc-mod or cabal install ghc-mod
• Install modified version of lushtags.
• Put neco-ghc-lushtags in the plugin directory (You probably use Pathogen, NeoBundle, vim-plug, deim.vim, etc).
• Copy bin/ghc-mod-cache into PATH (e.g., ~/.local/bin or ~/.cabal/bin).
• Install yaml/json modules for Python (Optional but highly recommended). pip install pyyaml and pip install json usually work. If pip is not available, type easy_install pip to install pip first. Python 2.x/3.x are both fine.

Note: If you use ghc-mod 5.4, you should use ghc-mod 5.5+. Because, ghc-mod 5.5 fixes the rootdir problem.

DanielG/ghc-mod#665

Usage

neco-ghc-lushtags provides necoghc#omnifunc for omni-completion. I recommend adding the following in your ~/.vim/ftplugin/haskell.vim.

" Disable haskell-vim omnifunc
let g:haskellmode_completion_ghc = 0
autocmd FileType haskell setlocal omnifunc=necoghc#omnifunc

See :help compl-omni for details on omni-completion.

Completion engines

This plugin can be used as a source of neocomplete.vim or neocomplcache.vim or deoplete.nvim. You can enjoy auto-completions without any specific configuration.

This plugin also should work with YouCompleteMe, but not tested. To enable auto-completions, you have to add the following setting.

let g:ycm_semantic_triggers = {'haskell' : ['.']}

Options

g:necoghc_enable_detailed_browse

Default: 0

Show detailed information (type) of symbols. You can enable it by adding let g:necoghc_enable_detailed_browse = 1 in your vimrc. While it is quite useful, it will take longer boot time.

This feature was introduced in ghc-mod 1.11.5.

g:necoghc_debug

Default: 0

Show error message if ghc-mod command fails. Usually it will be noisy if ghc-mod browse Your.Project.Module always fails. Use this flag only if you have some trouble.

Troubleshoot

Q: neco-ghc-lushtags does not work

Check the $PATH variable in vim contains the path to your ghc-mod and stack command. Or you can execute :NecoGhcDiagnostics command for debug.

License

BSD3 License, the same license as ghc-mod and neco-ghc.