fix Error: is not a library defined function!

[farzonl]

library functions are the last thing we look up in a program, as a result if we hit enter we erroneously think a library function call was attempted and trigger an incorrect error. Fix the error so that we only trigger this error if we see something in the format <function_name> (<arguments>) i.e <function name> <open paren> <arguments> <close paren>