Use dict for custom backend, add docs

README.md

@@ -32,6 +32,12 @@ Some key features:
   The installation is local (not global!). This means that Intero is always
   current for each of your projects. The goal of Intero is to Just Work™.
 
+- **Bring Your Own GHCi**
+
+  You can configure the plugin to use a custom *backend*, e.g. `cabal repl` or
+  plain `ghci`, instead of the default Intero backend. Newer features are
+  enabled based on the GHCi version.
+
 - **On-the-fly Typechecking**
 
   Intero reports errors and warnings as you work on your file using the Neomake
@@ -149,6 +155,27 @@ augroup END
 let g:intero_start_immediately = 0
 ```
 
+## Using a Custom Backend
+
+The default Intero backend can be overriden, so that you can use this plugin
+without Stack and Intero. The following configuration uses `cabal new-repl`,
+and specifies a `cwd` for a sub-directory project:
+
+``` vim
+let g:intero_backend = {
+        \ 'command': 'cabal new-repl',
+        \ 'options': '-Wall',
+        \ 'cwd': expand('%:p:h')
+        | }
+```
+
+Such configuration can be set per-project using a [local .nvimrc
+file](https://andrew.stwrt.ca/posts/project-specific-vimrc/), or in your init
+file for a system-wide effect.
+
+**NOTE:** If `g:intero_backend` is set, `g:intero_ghci_options` and
+`g:intero_load_targets` have no effect.
+
 ## Caveats
 
 - Running `:Neomake!` directly will not work. You need to run `:InteroReload`

autoload/intero/process.vim

@@ -42,7 +42,7 @@ function! intero#process#initialize() abort
         echom 'Neomake not detected. Flychecking will be disabled.'
     endif
 
-    if(!s:uses_custom_ghci())
+    if(!s:uses_custom_backend())
         call s:ensure_intero_is_installed()
     endif
 
@@ -56,7 +56,7 @@ function! intero#process#start() abort
 
     call intero#process#initialize()
 
-    if !s:uses_custom_ghci() && (!exists('g:intero_built') || g:intero_built == 0)
+    if !s:uses_custom_backend() && (!exists('g:intero_built') || g:intero_built == 0)
         echom 'Intero is still compiling'
         return -1
     endif
@@ -134,8 +134,8 @@ function! intero#process#restart() abort
 endfunction
 
 function! intero#process#restart_with_targets(...) abort
-    if s:uses_custom_ghci()
-        throw 'Targets is not supported when using a custom GHCi command.'
+    if s:uses_custom_backend()
+        throw 'Selecting targets is not supported when using a custom GHCi backend.'
     end
 
     if a:0 == 0
@@ -151,8 +151,8 @@ endfunction
 " Private:
 """"""""""
 
-function! s:uses_custom_ghci() abort
-    return exists('g:intero_ghci_command')
+function! s:uses_custom_backend() abort
+    return exists('g:intero_backend')
 endfunction
 
 function! s:start_compile(height, opts) abort
@@ -373,9 +373,17 @@ function! s:build_terminal_invocation() abort
                 \ 'on_stdout': function('s:on_stdout'),
                 \ }
 
-    if s:uses_custom_ghci()
-        " Override to use a custom GHCi command.
-        let l:terminal_command = g:intero_ghci_command
+    if s:uses_custom_backend()
+        " Override to use a custom GHCi backend.
+        let l:terminal_command = g:intero_backend.command
+        " Add options if set.
+        if has_key(g:intero_backend, 'options')
+            let l:terminal_command .= ' ' . g:intero_backend.options
+        endif
+        " Use user-specified cwd if set.
+        if has_key(g:intero_backend, 'cwd')
+            let l:terminal_options.cwd = g:intero_backend.cwd
+        endif
     else
         " Use the default Intero invocation.
         let l:terminal_ghci_options = []

doc/intero.txt

@@ -256,7 +256,7 @@ different stack project than you were in initially, you may want to call
                   list.
 
                                                        *:InteroUseAllTargets*
-:InteroUseAllTargets 
+:InteroUseAllTargets
                   This loads all targets specified by `stack ide targets`.
 
                                                        *:InteroClearTargetCache*
@@ -323,6 +323,27 @@ g:intero_ghci_options
 
   Options that configure the behaviour of GHCi. For example, -fobject-code.
 
+*g:intero_backend*
+
+  Overrides the default `intero` backend with a custom one. Specified as a
+  dict: >
+      let g:intero_backend = {
+              \ 'command': 'ghci',
+              \ 'options': '-Wall',
+              \ 'cwd': expand('%:p:h')
+              | }
+<
+  The following keys are supported:
+
+  * `'command'`: the command to start a GHCi REPL, e.g. `cabal repl` or
+    `ghci`.
+  * `'options'`:  a string of command-line arguments to the command (optional)
+  * `'cwd'`: specifies the current working directory of the GHCi
+    process (optional)
+
+  If `g:intero_backend` is set, `g:intero_ghci_options` and
+  `g:intero_load_targets` have no effect.
+
 =============================================================================
 CAVEATS                                                       *intero-caveats*