Error found:
in module Main
at tests/purs/failing/IntToString1.purs:14:15 - 14:46 (line 14, column 15 - line 14, column 46)

  Could not match type
       
    "1"
       
  with type
       
    "a"
       

while solving type class constraint
                       
  Prim.Int.ToString 1  
                    "a"
                       
while applying a function testToString
  of type ToString t0 t1 => Proxy @Int t0 -> Proxy @Symbol t1
  to argument Proxy
while checking that expression testToString Proxy
  has type Proxy @Symbol "a"
in value declaration posToString

where t0 is an unknown type
      t1 is an unknown type

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