A flycheck checker that runs the haskell variant of doctest

flycheck-haskell-doctest.el

  (flycheck-define-checker haskell-doctest
  "Haskell doctest checker"
  :command ("doctest" source)
  :error-patterns
  ((error line-start "### Failure in " (file-name) ":" line ":" ;;line-end)
            (message (one-or-more not-newline)
                     (one-or-more "\n"
                                  (or (one-or-more " ")
                                      "expected")
                                  (one-or-more not-newline))
                     line-end)))
  :modes haskell-mode)
 (flycheck-add-next-checker 'haskell-hlint '(info . haskell-doctest))
 (add-to-list 'flycheck-checkers 'haskell-doctest 'append)
;; Errors are expected to look something like this:
;; ### Failure in Wat.hs:43: expression `Nothing :: Maybe Int'
;; expected: Just 3
;;  but got: Nothing
;; Examples: 12  Tried: 6  Errors: 0  Failures: 2