Add options to configure indentation

README.md

@@ -10,6 +10,32 @@
 ## Installation
 Install with your favorite plugin manager.
 
+## Options
+If you don't like the default indentation you can easily change it by creating the following variables.
+
+Here are some examples:
+
+* `let g:haskell_indent_do = 3`
+
+      do
+      >>>foo
+
+* `let g:haskell_indent_if = 2`
+
+      if foo
+      >>then bar
+      >>else baz
+
+* `let g:haskell_indent_case = 2`
+
+      case foo of
+      >>bar -> baz
+
+* `let g:haskell_indent_in = 1`
+
+      let x = 1
+      >in x
+
 ## Author
 itchyny (https://github.com/itchyny)
 

indent/haskell.vim

@@ -72,7 +72,9 @@ function! GetHaskellIndent() abort
 
   " in
   if line =~# '\v^\s*<in>'
-    return s:indent('\v^\s*<in>', '\v^.*<let>\s*\zs', 0, -1)
+    return exists('g:haskell_indent_in')
+          \ ? s:indent('\v^\s*<in>', '\v^.*\zs<let>', 0, -1) + g:haskell_indent_in
+          \ : s:indent('\v^\s*<in>', '\v^.*<let>\s*\zs', 0, -1)
   endif
 
   " =
@@ -124,7 +126,7 @@ function! GetHaskellIndent() abort
   endif
 
   if nonblankline =~# '\v<do>\s*%(--.*)?$'
-    return match(nonblankline, '\v^\s*%(<where>|.*<let>)?\s*\zs') + &shiftwidth
+    return match(nonblankline, '\v^\s*%(<where>|.*<let>)?\s*\zs') + get(g:, 'haskell_indent_do', &shiftwidth)
   endif
 
   if nonblankline =~# '\v<do>\s*[[:alnum:](]'
@@ -133,7 +135,9 @@ function! GetHaskellIndent() abort
 
   if line =~# '\v<if>' && line !~# '\v^\s*#'
     if line !~# '\v<then>'
-      return match(line, '\v.*<if>\s*\zs')
+      return exists('g:haskell_indent_if')
+            \ ? match(line, '\v.*\zs<if>') + g:haskell_indent_if
+            \ : match(line, '\v.*<if>\s*\zs')
     elseif line !~# '\v<else>'
       return match(line, '\v.*\zs<then>')
     endif
@@ -147,9 +151,13 @@ function! GetHaskellIndent() abort
         return indent(s:prevnonblank(v:lnum - 1)) + &shiftwidth
       endif
     else
-      return line =~# '\v<case>.*<of>\s*([[:alnum:](\"''\[]|-\d)'
-            \ ? match(line, '\v<case>.*<of>\s*\zs\S')
-            \ : match(line, '\v.*<case>\s*\zs')
+      if line =~# '\v<case>.*<of>\s*([[:alnum:](\"''\[]|-\d)'
+        return match(line, '\v<case>.*<of>\s*\zs')
+      else
+        return exists('g:haskell_indent_case')
+              \ ? match(line, '\v.*\zs<case>') + g:haskell_indent_case
+              \ : match(line, '\v.*<case>\s*\zs')
+      endif
     endif
   endif
 
@@ -465,8 +473,9 @@ function! s:indent_then() abort
   if lnum == 0 && col == 0
     return -1
   else
-    " consider adding option to decide where to indent 'then'
-    return match(getline(lnum)[col - 1:], '\v<if>\s*\zs') + col - 1
+    return exists('g:haskell_indent_if')
+          \ ? g:haskell_indent_if + col - 1
+          \ : match(getline(lnum)[col - 1:], '\v<if>\s*\zs') + col - 1
   endif
 endfunction