Negative numbers in pattern matches are syntax errors

[rtfeldman]

This is an sscce version of #1259

f x =
  case x of
    1 -> "ok"
    -1 -> "breaks parsing"
    _ -> "ok"

Gives a syntax error.

If you swap the -1 pattern with the previous line, everything compiles, so the problem seems to affect only patterns after the first one.

[yawaramin]

Workaround: wrap the -1 in parens: (-1).

[evancz]

Thanks for the SSCCE. Follow along in #1374

[evancz]

Okay, making this it's own thing again because all the other things in the meta issue are done.

For my future reference: I think it should only be possible to match on Int and I'm not sure if there are any languages that permit negative numbers in matches.

[JoeyEremondi]

Haskell allows it if it's parenthesized:

\(-3) -> 1 works on tryhaskell.org, but \-3 -> 1 gives a parse error.

OCaml works with or without parenthesis.