# m2comp step 1 — Coco/R syntax front end (tag: `m2comp-step1`)

## Goal

Fresh `m2comp/` project (distinct from `m2c/` at step 11): prove the
toolchain end to end before any language work — Coco/R grammar
→ generated scanner/parser/driver → `gm2 -fiso` build → test runner.
Lexer and parser are FULLY Coco/R-generated; no hand-written lexer.

## What was built

- `m2comp/src/M2comp.atg` — Modula-2 program modules:
  `MODULE` + `FROM/IMPORT`, `CONST/TYPE/VAR`, `PROCEDURE` (nested,
  value/`VAR` params, function result), local `MODULE`s (Wirth form:
  `[Priority]`, `[Export [QUALIFIED]]`), statements (assign/call, `IF`,
  `WHILE`, `REPEAT`, `LOOP/EXIT`, `FOR/BY`, `RETURN`), full expressions.
  Only check is the `MODULE`/`END` name match (error 202).
- Kowarsch adaptations (from `docs/`, arXiv:1809.07080): unary minus
  takes a `Factor` (§3.3: `-b+c` ok, bare `-b*c+a` rejected, parens
  required); abbreviated multi-dim arrays via comma index list with
  subrange-capable `IndexType` (§3.1 strict); no octal `B`/`C` suffixes
  (§2.1); `<>` kept (open, §2.2); `(*$ *)` still comments (open, §2.3/2.4).
- `m2comp/src/` holds ALL sources: `M2comp.atg`, `compiler.frm`
  (listing driver, no `SymTab`/`MGen` yet), `scanner.frm`,
  `parser.frm`, `FileIO.def/.mod` (copied from `m2c/`), generated
  `M2compS/M2compP/M2comp` (`.def/.mod`), `Hello.mod` (gm2 smoke test).
  Deleted as unnecessary: hand `M2Lex` (replaced by `M2compS`),
  unused `Err`, empty `build/`.
- `m2comp/build.sh` — regenerate (`CRFRAMES=src CR -m -C`),
  compile with `gm2 -fiso`, link via the two-phase module-list
  workaround; produces `./M2comp` (project root).
- `m2comp/run_tests.sh` — `expect_ok`/`expect_fail` on
  `tests/ok_minimal.mod`, `tests/ok_proc.mod` (local module,
  2-D abbreviated array, `-v+1`), `tests/bad_mismatch.mod` (202).

## Tests — 3/3

| test | result |
| ---- | ------ |
| ok_minimal | `MODULE M; BEGIN END M.` accepted |
| ok_proc | imports, `VAR`, 2-D array, proc + local module accepted |
| bad_mismatch | `END WrongName` rejected (`Incorrect source`) |

`gm2 -fiso src/Hello.mod` → `Hello m2comp (gm2 -fiso)` verified.

## Notes

- Grammar name `M2comp` keeps generated modules short
  (`M2compS`/`M2compP`/`M2comp`, no Coco/R truncation surprises).
- LL(1) fix: `FieldSeq = Field { ";" Field }` (first field mandatory,
  may be empty) — the fully-optional form made `END` ambiguous.
- ISO gotchas: no anonymous `ARRAY[0..63]` formals (open
  `ARRAY OF CHAR` in `GetIdent`); no whole-array `#` (name match via
  `Strings.Equal`, hence `IMPORT Strings` in the `.atg`).
- Step 2: `SymTab` (duplicate/undeclared, type checks 200/210-224,
  nested-`ARRAY OF ARRAY` long-form flag) + `MGen`/MC64 backend.