# m2compiler-V3 — modern Modula-2, Coco/R frontend, QBE backend

A from-scratch Modula-2 compiler in the Blaise spirit (phased,
test-guarded, self-hosting as the end goal): a Coco/R-generated
frontend in GNU Modula-2, a fresh QBE SSA backend, and a
length-prefixed runtime data model. Modern syntax follows the
Benjamin R10 specs where they don't break classic code
(Kowarsch/Redux cleanups: `#` not `<>`, `NOT/AND/OR` only, no
`B/C` octals, `0x` hex, `//` comments).

## Prerequisites

- GNU Modula-2 (`gm2 -fiso`; developed with GCC 16.0.1 experimental)
- Coco/R `CR` V1.53 (`CRBIN` env var, defaults to the sibling
  `CocoGm2/CR` used here)
- `qbe` (default target `amd64_sysv`; pin: `vendor/qbe-pin.txt`)
- `cc`, `timeout`, standard shell tools

## Build and test

```sh
cd compiler
./build.sh      # M2.atg -> scanner/parser/driver -> ./M2
./run_tests.sh  # M2 -> gen_ssa/*.ssa -> qbe -> cc -> exit codes
```

Pipeline per test: `./M2 tests/foo.mod` writes
`gen_ssa/FOO.ssa`; a global `VAR ExitCode : INTEGER` selects the
process exit code (else 0). Reject tests assert on `.LST` messages;
every error also prints as `file:line:col: message` on stdout.

## Layout (Blaise-adapted)

```text
compiler/src/      M2.atg, frames, FileIO, SymTab, QbeGen (+ generated)
compiler/tests/    t_*.mod (check/reject/run) + showcase<N>.mod tours
compiler/gen_ssa/  build outputs (gitignored)
runtime/syslib/    always-linked runtime (SYSTEM, Storage, SysIO, …)
stdlib/            opt-in libraries (Strings, TextIO, …; classic form)
tools/             syntax helpers (redux-check direction)
bootstrap/         stage1/2/3 + fixpoint.sh (self-hosting proof)
vendor/            qbe toolchain pin
docs/              plan.md, summary_stepN.md (one file per step)
```

## Language status (at v3-step4.3, 87/87 green)

Lowers today: program modules; `CONST`/`VAR`/`TYPE` (scalars,
subranges, enums declared, arrays, records, sets, pointers);
`ARRAY`/`RECORD`/`SET`/`POINTER`, `WITH`, `IN`; whole
array/record copy; `NEW`/`DISPOSE`; all scalar arithmetic,
relations, boolean connectives; `IF/CASE/WHILE/REPEAT/LOOP/FOR`;
procedures with value/`VAR` params, functions, recursion,
`FORWARD`, nested procedures (static-link display); **separate
compilation** (`lib.def lib.mod prog.mod` in one run → one image,
`FROM`/`IMPORT`, qualified `L.x`, opaque-type completion).
Parse-now/lower-later (230): enum literals, Clarion-form `CLASS`
(declared + checked; class lowering pending), `HIGH`/`LEN`,
procedure-type variables.

Long-term rules already locked: every `ARRAY` is `LONGCARD` count
+ elements (all arrays, inline, element counts, no NUL);
`UCHAR` = 32-bit codepoint, `UString` = count + codepoints, UTF-8
at the edges with hard lex errors; self-hosting bar is
byte-identical `.ssa` over three stages.

## Working conventions

- Grammar grows section by section in `compiler/src/M2.atg`
  (kept LL(1)-clean — Coco/R must report no errors).
- Every step keeps the full suite green; per-step record in
  `docs/summary_stepN.md`; `showcase<N>.mod` tours each stage.
- Tags `v3-step1[.sub]` / `v3-step2` mark green states; no pushes
  without asking (see `git.txt` for the remote recipe).