Easytrieve Logical Expressions

Logical Connectors

Conditions You Can Connect

Logical connectors join conditions—not arbitrary expressions. Valid building blocks include relational comparisons (FIELD EQ value, FIELD GT value), series range conditions (FIELD EQ low THRU high), class conditions (FIELD NUMERIC, FIELD ZERO), and special constants (EOF, DUPLICATE) in input contexts. Each building block evaluates to true or false before AND OR combines them. IF GROSS GT 1000 AND STATUS EQ A AND EMPL-NUM NUMERIC stacks three condition types in one logical expression.

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IF STATUS EQ 'A' AND GROSS GT LIMIT
IF SERVICE EQ 1 THRU 5 OR SERVICE EQ 99
IF ACCT NUMERIC AND BALANCE GT 0

AND Expressions

AND means every connected condition in its group must pass. Payroll example: pay bonus only when status is active and gross exceeds threshold and department is not excluded. IF STATUS EQ A AND GROSS GT 5000 AND DEPT NE 999. One failing condition blocks the entire IF block. AND is appropriate for mandatory guards—numeric validation AND business rule AND authorization flag—all must be true before performing PUT or DISPLAY of sensitive data.

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IF GROSS NUMERIC AND DEDUCT NUMERIC AND GROSS GT DEDUCT
   NET = GROSS - DEDUCT
ELSE
   DISPLAY 'INVALID DEDUCTION' EMPL-NUM
END-IF

OR Expressions

OR means at least one connected condition must pass. Route record to exception processing when status is error or hold or gross is negative: IF STATUS EQ E OR STATUS EQ H OR GROSS LT 0. OR suits alternative valid values—department ten or twenty qualifies for union rule—IF DEPT EQ 10 OR DEPT EQ 20. Beware combining OR with AND without parentheses: IF A GT 0 AND B GT 0 OR C GT 0 may not mean what English prose suggests. See precedence section below.

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IF DEPT EQ 100 OR DEPT EQ 200 OR DEPT EQ 300
   PERFORM CORP-RULES
END-IF

NOT Expressions

NOT negates a condition in supported forms. Input loops commonly use DO WHILE NOT EOF to process until end of file. NOT may apply to constants and conditions per language reference for your release—not every comparison accepts NOT in all positions. When NOT readability suffers, flip the comparison: instead of NOT STATUS EQ A, use STATUS NE A if equivalent for alphabetic field.

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DO WHILE NOT EOF
  PERFORM PROCESS-RECORD
END-DO

Precedence: AND Before OR

Without parentheses, AND groups bind tighter than OR. Expression IF A GT 0 AND B GT 0 OR C GT 0 parses as (A GT 0 AND B GT 0) OR (C GT 0)—not as A GT 0 AND (B GT 0 OR C GT 0). Misunderstanding causes production bugs when OR alternatives should apply only to one AND guard. Use explicit parentheses whenever mixing connectors in maintenance-sensitive code. Dedicated order of evaluation and parentheses pages expand precedence tables with arithmetic mixed in.

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* Intended: A positive and (B or C positive)
IF A GT 0 AND (B GT 0 OR C GT 0)
   PERFORM ADJUST
END-IF

Parentheses for Grouping

Parentheses wrap subexpressions to override default precedence and to document intent for auditors. IF (STATUS EQ A OR STATUS EQ P) AND GROSS GT 0 requires active or pending status and positive gross. Nested parentheses are allowed within readability limits. Over ten nested levels signal refactor time—use PROC or flag fields set in prior lines.

Logical Expressions in DO WHILE

DO WHILE re-evaluates the logical expression each iteration. DO WHILE NOT EOF continues until EOF condition true. DO WHILE WS-COUNT LT 100 AND NOT DONE processes until count reaches hundred or DONE flag set. Ensure loop body eventually makes condition false— infinite loops from missing increment or EOF advancement still happen to beginners.

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WS-COUNT = 0
DO WHILE WS-COUNT LT 10 AND STATUS NE 'X'
  PERFORM PROCESS-SLICE
  WS-COUNT = WS-COUNT + 1
END-DO

Class Conditions in Logical Expressions

Class conditions—NUMERIC, ALPHABETIC, ZERO, POSITIVE, NEGATIVE—are atomic conditions in logical expressions. IF FIELD NUMERIC AND FIELD GT 0 validates before using field in later arithmetic inside the IF block. Combining class test with relational test is defensive pattern for FILE extract processing.

Series THRU in Logical Context

Range condition SERVICE EQ 6 THRU 10 is one condition true when SERVICE between six and ten inclusive. Combine with AND: IF SERVICE EQ 6 THRU 10 AND STATUS EQ A. Combine ranges with OR for multiple bands: IF CODE EQ 1 THRU 5 OR CODE EQ 90 THRU 99. THRU is inclusive on both ends per Broadcom documentation.

Replacing Complex Logic with Flags

When logical expression exceeds one screen line, set flag fields in prior statements. VALID-SW = Y after separate IF blocks that test each rule; final IF VALID-SW EQ Y PERFORM PAY. Easier to debug in production—DISPLAY which rule failed by setting different flag values. Logical expressions stay simple; business rules distribute across readable steps.

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VALID-SW = 'N'
IF GROSS NUMERIC
   IF STATUS EQ 'A'
      IF GROSS GT LIMIT
         VALID-SW = 'Y'
      END-IF
   END-IF
END-IF
IF VALID-SW EQ 'Y'
   PERFORM PAY-BONUS
END-IF

Logical vs Comparison Expressions

Comparison expression is one relational test—STATUS EQ A. Logical expression combines two or more conditions with AND OR NOT. IF STATUS EQ A is only comparison. IF STATUS EQ A AND GROSS GT 0 is logical expression containing two comparisons. Terminology helps when reading expressions overview and operator pages.

SQL and NULL in Logical Tests

SQL null state uses indicator variables—not logical NOT on field content. IF PHONE NULL tests indicator per SQL integration rules, distinct from IF PHONE EQ SPACE on host bytes. Mixing SQL null logic with batch FILE logical expressions in one program requires clear separation of host variable tests after fetch.

Common Logical Expression Mistakes

• AND OR precedence without parentheses—wrong branch taken.
• IF A AND B without relational operators on numeric fields.
• Using = instead of EQ inside conditions.
• Ten-condition line unmaintainable—refactor to flags.
• DO WHILE never false—infinite loop.
• NOT placement ambiguous—rewrite as NE or explicit parentheses.

Explain It Like I'm Five

Logical expressions ask combo questions. AND means every question must be yes—do you have a ticket and are you tall enough? OR means at least one yes—do you want cake or ice cream? NOT flips one question—are you NOT tired means you need to not be tired for yes. Easytrieve uses your combo answer to decide whether to run the instructions inside IF or keep looping in DO WHILE.

Exercises

1. Write IF with AND requiring status active and gross over limit.
2. Write IF with OR for three valid department codes.
3. Add parentheses to change meaning of A AND B OR C.
4. Convert complex AND chain to VALID-SW flag pattern.
5. Write DO WHILE NOT EOF with body incrementing counter.