Pretty-print infix constructors in pattern counterexamples using infix notation

[rureirureirurei]

Pretty-print infix constructors in pattern counterexamples using infix notation

When pattern matching is non-exhaustive, the compiler shows a counterexample. Currently, infix constructors like :: are printed in prefix notation with excessive parentheses:

fatal error: This pattern-matching is not exhaustive.
Here is an example of a case that is not matched:
  (::) _ ((::) _ _)

This should be printed as:

  _ :: _ :: _

Details

• Infix constructors are stored internally as "(::)" (parentheses-wrapped)
• Precedence is determined by first character (: -> level 70, + -> 80, * -> 90, etc.)