Encountered a function that was never defined.
          #2030   Compile-time error
          Encountered a function that was never defined.
Additional Information
The function 'X' was first predefined on line N of file 'F'.
The conversion function was first predefined on line N of file 'F'.
     in case the function was predefined with define conversion-function.
    
Recovery
      Compilation continues but no compiled source code file will be saved.
    
Explanation
All functions must be declared before they are used. The body of the function may be given anywhere in a
        program (thereby defining the function), but its heading must appear at least once before its first use.