Demo — RPN / expression calculator (mini spreadsheet)

Type: feature
Status: done — expression-evaluator core (commit 29e19cc); spreadsheet layer not built (was optional)
Owner: —
Opened: 2026-06-19
Relation: demo-class survivor from idea-demo-app-candidates (was catalog #4). Could lean on feature-bignum-library for exact-integer mode. Platonic source.

Goal

An expression calculator: parse infix expressions (Pratt or shunting-yard) and/or RPN, evaluate with an operator/function table. Optional mini-spreadsheet layer: named cells referencing each other, recomputed on change.

Surface / shape

tokenizer + parser (managed strings)
procedural-type op table (binary ops, functions like min/max/gcd)
evaluator over an expression tree (records + recursion)
optional: cell map (collection) + dependency recompute

Coverage

managed strings (parse) · records + dynamic arrays (AST) · procedural types (op/function table) · recursion (eval) · collections (spreadsheet cells) · short-circuit. Integer-deterministic core; float optional, kept out of the oracle path.

Acceptance / oracle

Fixed expression set → exact integer results, byte-identical across targets (e.g. 2+3*4, gcd(48,36), nested parens, RPN forms).
Spreadsheet slice: a fixed cell graph → fixed recomputed values.
Demo: examples/calc/ evaluates a bundled set; optional REPL over serial.

Constraints

Platonic source; no compiler changes; ESP32-fit. No self-host / cross regression.

Log

2026-06-19 — Opened in the demo-ticket organization pass.
2026-06-22 — DONE (track B), commit 29e19cc: lib/rtl/calc.pas integer expression evaluator — one-pass recursive-descent (no AST, to dodge the dynarray-in-record codegen bug), precedence/parens/unary, gcd/min/max/pow/abs, errors on syntax + div/mod-by-zero + unknown fn + trailing junk. Oracle examples/calc/calcdemo.pas runs ALL OK on pinned v33; wired into make lib-test + make demos. Used the json-style reader class (zero-init fields), which compiles cleanly — unlike the module-global sat unit that hit the layout-sensitive codegen bug. Not done: the optional mini-spreadsheet layer (named cells + dependency recompute) — file a follow-up if wanted.