Error found:
in module Main
at tests/purs/failing/MPTCs.purs:9:1 - 10:10 (line 9, column 1 - line 10, column 10)

  The type class Main.Foo expects 1 argument.
  But the instance fooStringString provided 2.

in type class instance
                 
  Main.Foo String
           String
                 

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