| name | legacy-cobol-explorer |
| description | Domain knowledge for the legacy COBOL accounting system used in Scenario 3 (cloned from github.com/tjsingh85/cobol-accounting-system into examples/scenario-3-legacy-cobol-library/cobol-source). Use when reading, explaining, or modernizing that program. |
Legacy COBOL explorer
This skill applies to the COBOL accounting system participants clone in Scenario 3 into
examples/scenario-3-legacy-cobol-library/cobol-source/ (source:
tjsingh85/cobol-accounting-system).
Use it whenever a participant or another agent needs to understand or modernize that program.
The source is not committed to this repo — it is cloned during the scenario. The
structure and rules below describe what you'll find once cloned.
What the program does
An interactive, menu-driven single-account accounting app, split across three COBOL programs:
main.cob (MainProgram) — the menu loop. Reads a choice (1-4) and calls the
operations subprogram with a 6-char operation code:
1 → TOTAL (view balance)2 → CREDIT3 → DEBIT 4 → exit
operations.cob (OperationsProgram) — performs the chosen operation: prompts for an
amount (credit/debit), reads/writes the balance via the data program, and prints results.data.cob (DataProgram) — stores the balance in working storage; supports READ and
WRITE operations.
There is no file I/O, database, or network — the balance lives in memory for the session.
Key facts to preserve in any rewrite
- Starting balance is
1000.00 (PIC 9(6)V99, i.e. up to 6 integer digits + 2 decimals,
unsigned).
- View balance prints
Current balance: <balance>.
- Credit prompts
Enter credit amount:, adds it, prints Amount credited. New balance: <balance>.
- Debit prompts
Enter debit amount:. If balance >= amount, subtract and print
Amount debited. New balance: <balance>. Otherwise print Insufficient funds for this debit.
and leave the balance unchanged (no overdraft, ever).
- Amounts are non-negative decimals with 2 implied decimal places.
- The balance is session-scoped — it resets to
1000.00 on each run (no persistence).
Modernization checklist
When rewriting this in a modern language (Scenario 3 targets Node.js):
- Mirror the three programs as small modules:
data (balance store), operations
(credit/debit/view with the overdraw guard), main (interactive menu loop).
- Keep the starting balance and the insufficient-funds rule identical.
- Reproduce the menu text and result messages so behavior matches the COBOL app.
- Use the repo's
TESTPLAN.md to derive tests: view balance, credit (valid + zero),
debit (valid + insufficient funds).
- Keep the cloned
cobol-source/ folder read-only — write the rewrite under modern/.
Things to NOT change
- The starting balance (
1000.00).
- The overdraft rejection rule (a debit larger than the balance is refused).
- The set of operations (view balance, credit, debit, exit).
