Update

indent/haskell.vim

@@ -113,24 +113,22 @@ function! GetHaskellIndent()
   let l:hlstack = s:getHLStack()
 
   " do not indent in strings and quasiquotes
-  if index(l:hlstack, 'haskellString') > -1 || index(l:hlstack, 'haskellQuasiQuote') > -1
+  if index(l:hlstack, 'haskellQuasiQuote') > -1 || index(l:hlstack, 'haskellBlockComment') > -1
     return -1
   endif
 
-  " blockcomment handling
-  if index(l:hlstack, 'haskellBlockComment') > -1
-    for l:c in range(v:lnum - 1, 0, -1)
-      let l:line = getline(l:c)
-      if l:line =~ '{-'
-        return 1 + match(l:line, '{-')
-      endif
-    endfor
-    return 1
-  endif
-
   let l:prevline = getline(v:lnum - 1)
   let l:line     = getline(v:lnum)
 
+  " indent multiline strings
+  if index(l:hlstack, 'haskellString') > -1
+    if l:line =~ '^\s*\\'
+      return match(l:prevline, '["\\]')
+    else
+      return - 1
+    endif
+  endif
+
   " reset
   if l:prevline =~ '^\s*$' && l:line !~ '^\s*\S'
     return 0