Make your own free website on Tripod.com
2.4.19 The RETURN Instruction
      RETURN [ expr ] ;

The RETURN instruction is used to terminate the current procedure
level, and return control to a level above. When RETURN is
executed inside one or more nesting construct, i.e. DO, IF, WHEN,
or OTHERWISE, then the nesting constructs (in the procedural
levels being terminated) are terminated too.

Optionally, an expression can be specified as an argument to the
RETURN instruction, and the string resulting from evaluating this
expression will be the return value from the procedure level
terminated to the caller procedure level. Only a single value can
be returned. When RETURN is executed with no argument, no return
value is returned to the caller, and then a SYNTAX condition {44}
is raised if the subroutine was invoked as a function.

Example: Multiple entry points

A routine can have multiple exit points, i.e. a procedure can be
terminated by any of several RETURN instructions.  A routine can
also have multiple entry points, i.e. several routine entry points
can be terminated by the same RETURN instruction.  However, this
is rarer than having multiple exit points, because it is generally
perceived that it creates less structured and readable code.
Consider the following code:

     call foo
     call bar
     call baz
     exit
     
     foo:
          if datatype(name, ’w’) then
               drop name
          signal baz
     bar:
          name = ‘foo’
     baz:
          if symbol(‘name’)== ’VAR’ then
               say ‘NAME currently has the value’ name
          else
               say ‘NAME is currently an unset variable’
          return

Although this is hardly a very practical example, it shows how the
main bulk of a routine can be used together with three different
entry points. The main part of the routine is the IF statement
having two SAY statements. It can be invoked by calling FOO, BAR,
or BAZ.

There are several restrictions to this approach. For instance, the
PROCEDURE statement becomes cumbersome, but not impossible, to
use.

Also note that when a routine has multiple exit points, it may
choose to return a return value only at some of those exit points.

When a routine is located at the very end of a source file, there
is an implicit RETURN instruction after the last explicit clause.
However, according to good programming practice, you should avoid
taking advantage of this feature, because it can create problems
later if you append new routines to the source file and forget to
change the implied RETURN to an explicit one.

If the current procedure level is the main level of either the
program or an external subroutine, then a RETURN instruction is
equivalent to an EXIT instruction, i.e. it will terminate the REXX
program or the external routine.  The table in the Exit section
shows the actions of both the RETURN and EXIT instructions
depending on the context in which they occur.


The SAY Instruction

     SAY [ expr ] ;

Evaluates the expression expr, and prints the resulting string on
the standard output stream. If expr is not specified, the
nullstring is used instead. After the string has been written, an
implementation-specific action is taken in order to produce an end-
of-line.

The SAY instruction is roughly equivalent to

     call lineout , expr

The differences are that there is no way of determining whether
the printing was successfully completed if SAY is used, and the
special variable RESULT is never set when executing a SAY
instruction. Besides, the effect of omitting expr is different.
In SAA API, the RXSIOSAY subfunction of the RXSIO exit handler is
able to trap a SAY instruction, but not a call to the LINEOUT()
built-in function. Further, the NOTREADY condition is never raised
for a SAY instruction.



PREV NEXT