SUB NUMERIC subroutine-name
SUB NUMERIC subroutine-name ( [ parameter-list ] )
SUB subroutine-name
SUB subroutine-name ( [ parameter-list ] )
SUB STRING subroutine-name
SUB STRING subroutine-name ( [ parameter-list ] )

   Synopsis:
      Declares a subroutine with a numeric or string return value

   Notes:
      A subroutine is called with a CALL statement. Execution moves to the first
         line after the SUB statement.
      The parameter list, if it is specified, contains a list of one or more
         scalar variables, which are used as local variables within the scope of
         the subroutine. More local variables in the same scope can be created
         with LOCAL or DIM LOCAL statements.
      When the subroutine is called, the variables in its parameter list are set
         to the values specified in the CALL statement's argument list. Both
         lists must have the same number of variables (which might be zero). If
         a value in the parameter list is numeric, the corresponding value in
         the argument list must also be numeric. If a value in the parameter
         list is a string, the corresponding value in the argument list must
         also be a string.

      All subroutines have a return value. The CALL statement can use that value
         or ignore it, as required.
      Subroutines declared with SUB NUMERIC return a numeric value and those
         declared with SUB STRING return a string value. If neither NUMERIC nor
         STRING are used, a numeric value is returned.
      You should use one or more RETURN statements to return the value you want.
         If the END SUB statement is executed first, the return value is either
         0 or an empty string.
      EXIT SUB behaves exactly like END SUB, except that whereas each subroutine
         can have only one END SUB statement, it can have as many EXIT SUB
         statements as you like. The subroutine's return value is again either
         an empty string or 0.

      A subroutine can occur anywhere in a script, including after the END
         statement. If the next line to be executed is a SUB statement,
         execution skips to the first line after the corresponding END SUB
         statement.
      See also the help for CALL, END, EXIT and RETURN.

   Availability:
      SUB is not available in scripts with primitive line numbers (the GOSUB
         statement can be used instead).

   Examples:
      LET number1 = 2
      LET number2 = 5
      LET result = CALL Multiply (number1, number2)
      PRINT result
      END

      SUB NUMERIC Multiply (val1, val2)
         RETURN (val1 * val2)
      END SUB
