Common Errors

parse error on input ‘-- | xxx’

This is probably caused by the -- | xxx comment not being before a declaration, see Documenting a Top-Level Declaration.

parse error on input ‘-- $ xxx’

You’ve probably commented out code like:

f x
  $ xxx

-- $ is a special syntax for named chunks, see (Named) Chunks of Documentation. You can fix this by escaping the $:

-- \$ xxx