cobol-patterns

name	cobol-patterns
description	COBOL anti-patterns, modernization signals, and risk patterns to identify during parsing and analysis. Use when evaluating COBOL code quality, flagging migration risks, or assessing programs for Java conversion feasibility.

COBOL Patterns Reference

Anti-Patterns (Flag During Parsing)

CRITICAL Risk — Flag immediately

Pattern	Identifier	Risk
ALTER verb	ALTER para-name TO PROCEED TO other-para	Self-modifying code — no automated migration path
GOTO with complex control flow	Multiple GOTOs across sections	Spaghetti control flow
REDEFINES on large groups	REDEFINES on 01-level items	Memory overlap — maps to complex union types

HIGH Risk

Pattern	Identifier	Risk
Deep PERFORM THRU	PERFORM A THRU Z spanning many paragraphs	Implicit flow coupling
Numeric GOTO (COMPUTED GO TO)	GO TO para1 para2 DEPENDING ON var	Switch via GOTO — complex to map
OCCURS DEPENDING ON	OCCURS 1 TO 100 DEPENDING ON counter	Dynamic arrays — need careful Java handling
Global working storage mutation	Paragraphs modifying 01-level items with no encapsulation	Hidden state — risk in concurrent Java

MEDIUM Risk

Pattern	Identifier	Risk
Implicit string padding	MOVE short-string TO long-string (COBOL pads with spaces)	Java Strings don't pad — behaviour change
Numeric truncation	MOVE large-pic TO small-pic	Java throws; COBOL truncates silently
INSPECT/STRING/UNSTRING	String manipulation verbs	Complex but mappable to String methods
Timezone-unaware date arithmetic	DATE-OF-INTEGER, INTEGER-OF-DATE without timezone	Careful Java LocalDate mapping needed

Modernization Signals (Positive Indicators)

Easy Migration Signals

• Single entry/exit paragraph structure (0000-MAIN → sub-paragraphs)
• No GOTO, no ALTER
• LINKAGE SECTION matches clean service interface
• Pure computational programs (no file I/O, no CICS)
• Small line count (<300 lines) with low coupling

Batch Job Signals (→ Spring Batch)

• OPEN INPUT ... OPEN OUTPUT patterns
• PERFORM UNTIL EOF loops
• READ ... AT END patterns
• No LINKAGE SECTION (no external callers)

Service/API Signals (→ Spring @Service or @RestController)

• Has LINKAGE SECTION parameters
• Called by many programs (high fan-in)
• No direct file I/O (delegates to other programs)

CICS Transaction Signals (→ REST API or Spring MVC)

• EXEC CICS SEND/RECEIVE MAP
• EXEC CICS RETURN TRANSID
• EXEC CICS READ/WRITE

For complexity scoring heuristics, read ANTI-PATTERNS.md

For migration readiness rubrics, read MODERNIZATION-SIGNALS.md