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Esoteric probe: COBOL

What it is

Verbose, deliberately English-like business language. Programs are split into DIVISIONs (IDENTIFICATION/ENVIRONMENT/DATA/PROCEDURE), with data declared via PICTURE clauses describing fixed-format decimal/text layouts (PIC 9(5)V99 = a 5-digit-plus-2-decimal fixed-point number) rather than ordinary type names.

Why it's a good probe

The "closest to human expression" thread from this session's brainstorm, for real this time — COBOL was explicitly designed to read like English business prose. Structurally it's the most different candidate on this list: no functions-as-primary-unit (DIVISION-structured instead), and PICTURE-clause fixed-decimal data has no direct equivalent in PXX's type system (closest is manual scaled-integer arithmetic) — good diversity for the fuzz-probe goal.

Scope (skeleton only — see umbrella for the category rule)

Lexer + parser for a minimal 4-division skeleton + DISPLAY (COBOL's VISIBLE-equivalent) + a couple of PIC 9(n) integer variables — no fixed-decimal (V99-style) arithmetic in v1, no file/record I/O. Stop once a trivial "hello world"-shaped program compiles and runs, or a shared bug surfaces trying to get there.

Scope relaxed further (2026-07-05)

COBOL isn't part of the narrowed "valid" core test surface (Pascal, C, BASIC, Python/Nil-Python — see [[feature-esoteric-frontend-probes]]'s "Core vs opportunistic" note), so a compiled-IR skeleton is no longer required to justify this ticket. An interpreter (Pascal-hosted, same shape as examples/lisp/lispdemo.pas) is an equally acceptable outcome — whichever is more convenient when this is picked up. Unlike Lisp, this isn't because COBOL has a paradigm-mismatch reason to prefer interpreting (it's still squarely imperative/static under the verbosity) — it's a pragmatic scope call now that COBOL sits outside the core set.

Acceptance

Either: (a) a shared IR/codegen/ABI bug is found and filed as its own Track A ticket, or (b) the trivial subset compiles and runs clean — both close this probe successfully.

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