Easytrieve EXIT Control Flow

EXIT in the Control Flow Model

PERFORM transfers control into PROC module. Normal path executes all statements until implicit return at END-PROC boundary. EXIT shortcut jumps to return without executing intervening statements. Caller resumes after PERFORM. Multiple PERFORM paths may hit different EXIT points or fall through full body. Flow diagram shows EXIT as branch leaving PROC box early back to caller.

BEFORE-SCREEN EOF Pattern

Screen cycle GET from master file: IF EOF, set message, EXIT—skip field MOVE and cursor setup that require valid record. Control returns to screen engine; END-PROC still ends module in source. Without EXIT, MOVE from empty buffer corrupts screen or abends. Same pattern in BEFORE procedures when prescreen determines record unusable—EXIT after error MESSAGE instead of running SELECT tail.

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BEFORE-SCREEN. PROC
  GET MASTER
  IF EOF MASTER
     MSG = 'NO MORE RECORDS'
     EXIT
  END-IF
  MOVE NAME TO SCR-NAME
  MOVE BAL  TO SCR-BAL
END-PROC

IF ... EXIT Guard Clauses

Guard clause style: IF invalid-condition, EXIT, END-IF at PROC top—main logic below assumes preconditions met. Reduces nesting versus IF valid ... large block END-IF. Limit stacked guard EXITs to three; beyond that use CASE or PERFORM sub-procs. Each guard EXIT must represent mutually exclusive failure mode documented in proc header comment.

EXIT Versus END-PROC in Source

Runtime EXIT skips statements; compile-time module still needs END-PROC after all statements including unreachable-on-EXIT tail if present in source. Tail after EXIT may hold shared cleanup—if cleanup must always run, place before EXIT or in caller after PERFORM. Confusing EXIT with END-PROC causes missing terminator compile errors when developer deletes END-PROC thinking EXIT closed module.

EXIT Inside Loops via PERFORM

DO WHILE loop PERFORM SEARCH-PROC; inside SEARCH-PROC, EXIT when found—returns to loop body after PERFORM, loop continues unless caller sets FOUND and WHILE condition stops. EXIT does not break DO loop directly. Pattern: PERFORM sets FOUND Y, loop condition includes FOUND EQ N, or GOTO after END-DO in caller when PERFORM reports success via flag field.

EXIT and SELECT in Sort BEFORE

Invalid record: EXIT without SELECT excludes from sort output and skips remaining BEFORE logic. Valid record: SELECT at end. IF error EXIT early avoids accidental SELECT in fall-through tail. Order IF validation, EXIT, processing, SELECT documents inclusion pipeline clearly.

When Not to Use EXIT

• Short PROC with one IF—use ELSE instead of EXIT.
• Cleanup must run on all paths—use IF structure or caller finally pattern.
• Replacing END-PROC—invalid; module must close.
• Cross-activity jump—use GOTO within activity rules not EXIT from wrong PROC context.

Testing EXIT Paths

1. PERFORM path hitting EXIT—confirm tail statements did not run.
2. PERFORM path not hitting EXIT—full body executes.
3. Caller state valid after EXIT return.
4. EOF and error guards trigger EXIT in screen test.
5. No resource leak when EXIT skips CLOSE—CLOSE must be elsewhere if needed.

Explain It Like I'm Five

EXIT is leaving the recipe early when you realize you are out of eggs. You stop reading the rest of that recipe card and go back to whoever asked you to cook. The recipe card still has an END at the bottom on the paper—you just did not do every step this time. You need another way to finish dinner if steps after EXIT were important.

Exercises

1. Write BEFORE-SCREEN PROC with GET EOF EXIT pattern.
2. Refactor nested IF to guard EXIT at PROC top.
3. Diagram PERFORM/EXIT return to caller loop.
4. List difference EXIT END-PROC GOTO STOP RUN.
5. Move required cleanup before EXIT in flawed example.