haskell

Haskell

This plugin has support for sending Haskell source code to ghci.

Sending normal code

To support older GHC versions, code is processed in order to comply with the syntax rules that are specific to interactive mode. For instance when sending the following snippet to ghci:

-- make in triplicate
f :: a -> [a]
f = replicate 3

This translates to the following:

:{
let f :: a -> [a]
    f = replicate 3
:}

Some of this behavior can be selectively turned off so that what is run is more faithful to the actual code in your buffer, but requires a recent enough GHC:

• let g:slime_haskell_ghci_add_let = 0 disables the transformation of top-level bindings into a let binding; requires GHC 8.0.1 or later

Sending GHCi scripts

All of this is very nice but my workflow sometimes requires that I send the same code to ghci over and over, so I usually put it in a separate "script" file that holds some testing instructions so I can send them quickly.

However since some of the syntax is different between interactive and normal Haskell and I write these script files as if I were writing in ghci, sometimes the syntax translation would get in the way. E.g. I would write a function call to test a certain function and check it's type:

(++) "This is a: " "TEST"
:type (++)

and it get translated to:

:{
let (++) "This is a: " "TEST"
    :type (++)
:}

which is not what I wanted obviously.

To get around this, there is another handler that only kicks in if the filetype in vim is set to haskell.script. If you want access to this handler call set ft=haskell.script or create a new ftdetect file which does this for you for a certain file extension. For instance, I have:

au BufRead,BufNewFile,BufNew *.hss setl ft=haskell.script

in ~/.vim/ftdetect/hss.vim.