Add dhall, closes #426

after/syntax/haskell.vim

@@ -0,0 +1,17 @@
+if exists('g:polyglot_disabled') && index(g:polyglot_disabled, 'dhall') != -1
+  finish
+endif
+
+" store and remove current syntax value
+let old_syntax = b:current_syntax
+unlet b:current_syntax
+
+syn include @dhall syntax/dhall.vim
+unlet b:current_syntax
+
+syn region dhallBlock matchgroup=quasiQuote start=/\[\$\?staticDhallExpression|/       end=/|\]/ contains=@dhall
+
+hi def link quasiQuote Underlined
+
+" restore current syntax value
+let b:current_syntax = old_syntax