Compaq AA-PWCBD-TE Procedures That Return a Result, Example 4-6 Procedure That Returns a Result

Lexical Elements of the DEC Text Processing Utility Language 4.9 Reserved Words

4.9.4.5 Procedures That Return a Result

Procedures that return a result are called function procedures. Example 4–6 shows a procedure that returns a true ( 1 ) or false ( 0 ) value.

Note

All DECTPU procedures return a result. If they do not do so explicitly,

DECTPU returns 0.

Example 4–6 Procedure That Returns a Result

PROCEDURE user_on_end_of_line !test if at eol, return true or false

IF CURRENT_OFFSET = LENGTH (CURRENT_LINE) ! we are on eol

THEN

user_on_end_of_line := 1	! return true
ELSE
user_on_end_of_line := 0	! return false
ENDIF;
ENDPROCEDURE;

Another way of assigning a value of 1 or 0 to a procedure is to use the DECTPU RETURN language statement followed by a value. See Example 4–13.

You can use a procedure that returns a result as a part of a conditional statement to test for certain conditions. Example 4–7 shows the procedure in Example 4–6 within another procedure.

Example 4–7 Procedure Within Another Procedure

PROCEDURE user_nested_procedure

.

.

.

IF user_on_end_of_line = 1! at the eol mark

THEN

MESSAGE ("Cursor is at the end of the line")

ELSE

MESSAGE ("Cursor is not at the end of the line")

ENDIF;

.

.

.

ENDPROCEDURE;

4.9.4.6 Recursive Procedures

Procedures that call themselves are called recursive procedures. Example 4–8 shows a procedure named user_reverse that displays a list of responses to the READ_LINE built-in procedure in reverse order. Note the call to the procedure user_reverse within the procedure body.

4–18Lexical Elements of the DEC Text Processing Utility Language