Add README.md

Author: bitc

README.md

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+hdevtools Vim Plugin
+====================
+
+Vim plugin for Haskell development powered by the lightnight fast
+[hdevtools](<https://github.com/bitc/hdevtools/>) background server.
+
+
+About
+-----
+
+[hdevtools](<https://github.com/bitc/hdevtools/>) is a command line program
+powered by the GHC API, that provides services for Haskell development.
+hdevtools works by running a persistent process in the background, so that your
+Haskell modules remain in memory, instead of having to reload everything each
+time you change only one file. This is just like `:reload` in GHCi - with
+hdevtools you get the speed of GHCi as well as tight integration with your
+editor.
+
+This is the Vim plugin that integrates Vim with hdevtools.
+
+
+Installation
+------------
+
+1. You must install the `hdevtools` command line program, It can be found
+   here: <https://github.com/bitc/hdevtools/>, or from Hackage:
+
+        $ cabal install hdevtools
+
+2. Install this plugin. [pathogen.vim](<https://github.com/tpope/vim-pathogen/>)
+   is the recommended way:
+
+        cd ~/.vim/bundle
+        git clone https://github.com/bitc/hdevtools.git
+
+3. Configure your keybindings in your `.vimrc` file. I recommend something
+   like:
+
+        au FileType haskell nnoremap <buffer> <F1> :HdevtoolsType<CR>
+        au FileType haskell nnoremap <buffer> <silent> <F2> :HdevtoolsClear<CR>
+
+
+Features
+--------
+
+### Type Checking ###
+
+The best feature of the hdevtools command is near-instant checking of Haskell
+source files for errors - it's fast even for huge projects.
+
+This Vim plugin does not have direct support for interacting with this feature.
+Instead, I recommend using the excellent
+[Syntastic](<https://github.com/scrooloose/syntastic>) plugin.
+
+### Type Information ###
+
+Position the cursor anywhere in a Haskell source file, and execute
+`HdevtoolsType` (or press the `<F1>`) key if you have configured as above).
+
+The type for the expression under the cursor will be printed, and the
+expression will be highlighted. Repeated presses will expand the expression
+that is examined.
+
+You can execute `HdevtoolsClear` to get rid of the highlighting.
+
+Customization
+-------------
+
+You can set the `g:hdevtools_options` variable to pass custom options to
+hdevtools.
+
+This is useful for passing options through to GHC with the hdevtools `-g`
+flag. For example, if your project source code is in a `src` directory,
+and you want to use the GHC option `-Wall`, then stick the following somewhere
+appropriate (such as your project's `Session.vim`):
+
+    let g:hdevtools_options = '-g-isrc -g-Wall'
+
+Make sure that each GHC option has its own `-g` prefix (don't group multiple
+options like this: `"-g-isrc\ -Wall"`)
+
+
+Credits
+-------
+
+Parts of the design of this plugin were inspired by
+[ghcmod-vim](<https://github.com/eagletmt/ghcmod-vim/>), and large amounts of
+code were also taken.