``` 100 PROC tl$(x$(),5):STOP 110 DEFPROC tl$(REF input$(),index=1) 120 input$(index) = input$(index)(2 TO) 130 ENDPROC ``` On the example above **index** is not passed by reference and therefore it can have a default value. Note that integer variables and arrays cannot be passed by reference!!! ### Reading parameters with DATA and READ A **PROC** may call a **DEFPROC** with more parameters than the **DEFPROC** requires. In this case, if the **DEFPROC** has the keyword **DATA** as its final parameter, the procedure may read the additional parameters one at a time using **READ**. The new function **DATA** (see also *Chapter 5*) can be used to determine if there are further **PROC** parameters left to read. As an example: ``` 100 PROC printem(“Digits”,0,1,2, 3,4,5,6,7,8,9):STOP 110 DEFPROC printem(name$, DATA) 115 LOCAL n 120 PRINT name$ 130 REPEAT:WHILE DATA 140 READ n:PRINT n 150 REPEAT UNTIL 0 160 RETURN ``` ### Trapping errors locally As well as (or instead of) having a global error-trapping routine for your program as exhibited at the end of *Chapter 1, each procedure, subroutine and repeat loop may have its own local error-trapping routine, simply by using the* **ON ERROR** command within it. When an error occurs within a repeat loop, subroutine or procedure, it will be trapped by its own **ON ERROR** routine if there is one. If not, the error will be passed out to the next level and trapped by any **ON ERROR** routine there and so on. Only if there is no **ON ERROR** at any level above the command that caused the error will a normal error report be generated. For example: ``` 10 ON ERROR PRINT "Outer error handler!":ERROR 20 REPEAT 30 PRINT "Starting..." 40 ON ERROR PRINT "Oops!":ON ERROR:STOP 50 GO SUB 100 60 PRINT "Iterating..." 70 ON ERROR 80 REPEAT UNTIL 0 90 STOP 100 ON ERROR PRINT "Bad pigs!":RETURN ```