fix Error:  is not a library defined function!

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>`