# P6 Pascal validator pilot

`p6_pascal.atg` describes Wirth's Pascal-P6 (1980) compiler input. It
shares the P4 skeleton (same repair pass: quoted `";"` literals,
terminated productions, no `""` empties, no `ident`/token double
definitions, no reserved words as productions, start production
matching `COMPILER`, left-recursion removal, filled-in undefined
nonterminals, merged duplicate branches, lenient list shapes) plus its
own deltas, all diagnosed against `fpc -Miso` as oracle:

- `EnumType` (`(red, green, blue)`) alongside the other types.
- `ParamType` (`array[expr] of T`, expression bounds) merged with
  `ArrayType` into a single `Bound` form (`SimpleType` for
  `array[boolean]`-style index types, `Expr [".." Expr]` for ranges
  and computed bounds) — the two `array[`-led productions generated
  duplicate `CASE` labels and would not compile separately.
- `ProcSection` (`proc`-led procedural-type form) kept reachable via
  `StructType`.
- `Label = pnumber | ident` (enum case labels), with statement labels
  kept numeric-only — an optional `[Label ":"]` prefix commits on
  `ident` and then chokes on `:=`, so `i := 1` would break; `fpc`
  rejects ident-statement-labels anyway.
- P4's `preal`/`CONTEXT("..")`/subrange `TypeIdent` upgrade carried
  over (floats, `0..255`, `N..M`, dotted names).

The generated parser gets a strict EOF check
(`IF sym # 0 THEN SynError(0)` after the start symbol in `Parse`,
patched in by `build.sh` with a loud assertion): without it, the
Coco/R driver never scans past the program's final `.`, silently
ignoring trailing garbage — and worse, masking any failure that
leaves a `.` behind (e.g. unhandled float syntax). This makes the
validator marginally stricter than `fpc`, which accepts trailing junk
after `END.` — degenerate input only, documented here.

Two benign LL(1) warning families remain (dangling-`ELSE`, loop-exit
`";"` greediness — both resolve correctly).

`if`/`while`/`for` branches take a single `Statement` (standard Pascal
— plural branches greedily swallow the `;` separating `case` items),
and `begin..end` compounds are statements in their own right.

## Build

```sh
./build.sh        # -> build/P6 (build/ is git-ignored)
```

Needs `CR` (Coco/R), `gm2 -fiso`, the `parser.frm`/`scanner.frm`
frames and `FileIO.def/.mod` — all resolved from the environment with
sensible defaults (`CRFRAMES`, `M2LIB`, `CR`, `GM2`).

## Differential results (P6 vs `fpc -Miso`)

Accept battery (transferred from P4) + `tests/deep.pas` (enums,
records, subrange-free shapes, nested routines, labels/goto, all
statements): **0 false positives**. Broken mutants: **0 missed**,
positions close.