Error found:
in module Main
at tests/purs/failing/LetPatterns3.purs:11:7 - 11:8 (line 11, column 7 - line 11, column 8)

  Data constructor Main.X was given 0 arguments in a case expression, but expected 1 arguments.
  This problem can be fixed by giving Main.X 1 arguments.

while inferring the type of \$0 ->          
                              \b ->         
                                case $0 b of
                                  X b -> ...
in value declaration x

See https://github.com/purescript/documentation/blob/master/errors/IncorrectConstructorArity.md for more information,
or to contribute content related to this error.