There is an unfortunate ambiguity between list comprehension syntax and quasi-quotation. Consider the following with and without `-XQuasiQuotes` (noted [here](https://github.com/haskell/haskell-mode/issues/1185#issuecomment-192624592), ```hs let x = [ v | v <- [1,2,3]] let x = [v| v <- [1,2,3]] ``` While the former is always a list comprehension, the latter is a quasi-quote when `-XQuasiQuotes` is enabled. The original quasi-quoting syntax required a dollar sign before the quoter, although this was dropped in 26f164e5759e9eca73deb0531ddec422d36a6924. 9ba922ee06b048774d7a82964867ff768a78126e suggests that the old dollar sign syntax is slated for eventual removal. Unfortunately, given it has been five years since the requirement for a dollar sign was dropped I suspect it's a bit late to revert to the previous syntax. This ticket is simply meant to document the fact that this ambiguity exists. <details><summary>Trac metadata</summary> | Trac field | Value | | ---------------------- | ----------------- | | Version | 7.10.3 | | Type | Bug | | TypeOfFailure | OtherFailure | | Priority | low | | Resolution | Unresolved | | Component | Compiler (Parser) | | Test case | | | Differential revisions | | | BlockedBy | | | Related | | | Blocking | | | CC | | | Operating system | | | Architecture | | </details> <!-- {"blocked_by":[],"summary":"Quasi-quoting syntax is ambiguous with list comprehensions","status":"New","operating_system":"","component":"Compiler (Parser)","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"7.10.3","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"There is an unfortunate ambiguity between list comprehension syntax and quasi-quotation. Consider the following with and without `-XQuasiQuotes` (noted [[https://github.com/haskell/haskell-mode/issues/1185#issuecomment-192624592|here]],\r\n{{{#!hs\r\nlet x = [ v | v <- [1,2,3]]\r\nlet x = [v| v <- [1,2,3]]\r\n}}}\r\n\r\nWhile the former is always a list comprehension, the latter is a quasi-quote when `-XQuasiQuotes` is enabled.\r\n\r\nThe original quasi-quoting syntax required a dollar sign before the quoter, although this was dropped in 26f164e5759e9eca73deb0531ddec422d36a6924.\r\n\r\n9ba922ee06b048774d7a82964867ff768a78126e suggests that the old dollar sign syntax is slated for eventual removal.\r\n\r\nUnfortunately, given it has been five years since the requirement for a dollar sign was dropped I suspect it's a bit late to revert to the previous syntax. This ticket is simply meant to document the fact that this ambiguity exists.","type_of_failure":"OtherFailure","blocking":[]} -->