Error found:
in module Main
at tests/purs/failing/SkolemEscape.purs:8:1 - 8:19 (line 8, column 1 - line 8, column 19)

  The type variable a, bound at

    tests/purs/failing/SkolemEscape.purs:8:18 - 8:19 (line 8, column 18 - line 8, column 19)

  has escaped its scope, appearing in the type
                        
    (a0 -> a0) -> Number
                        

in the expression \x ->  
                    foo x
in value declaration test

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