Error found:
in module Main
at tests/purs/failing/4024-2.purs:10:8 - 10:13 (line 10, column 8 - line 10, column 13)

  No type class instance was found for
                   
    Main.Foo t2    
             t3    
             String
                   
  The instance head contains unknown type variables. Consider adding a type annotation.

while applying a function bar
  of type Foo @t0 @t1 @Type t2 t3 String => Int -> String
  to argument 0
while checking that expression bar 0
  has type String
in value declaration test

where t0 is an unknown type
      t1 is an unknown type
      t2 is an unknown type
      t3 is an unknown type

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