# Ulm-Oberon validator pilot

`ulm_oberon.atg` describes classic Oberon as implemented by `ulmo`,
ported from the reference (`Grammars/Ulm/Ulml-Oberon.atg`, extracted
from ulmo's own `OberonParser`). The reference is written for a newer
Coco/R generation (`/* */` comments, implicit whitespace), so the
port starts with: comment conversion, explicit `IGNORE CASE`,
`IGNORE CHR(9)..CHR(13)`, `COMMENTS FROM "(*" TO "*)" NESTED`, and a
`CHR(10)` `eol` set. It then needed the same repair family as the
Oberon-2 pilot, all diagnosed against `ulmo` (frontend verdicts
only — its backend crashes with an assertion on valid code, exit
still 0, so the harness reads `**` markers, never exit codes):

1. Duplicate `CASE` labels in `statement`: ident-led `assignment`
   vs `ProcedureCall` merged into `IdentTail`.
2. The optional-prefix trap in `qualident` (`[ident "."]` committed
   on any identifier): `ident { "." ident }`.
3. The designator guard `"(" qualident ")"` shadowed calls with
   non-identifier arguments: `"(" [ ExpList ] ")"`.
4. Missing `;` after the module header ident (reference parses
   `MODULE T` then expects `END`).
5. `DEFINITION` modules need bodyless procedures, but an optional
   body greedily eats the module's `END`: split into
   `DefinitionModule` (bodyless `DefProcDecl`) vs `Module`
   (body required) — disjoint `DEFINITION`/`MODULE` keywords, no
   greediness possible.
6. Strings are `"`-quoted in Ulm Oberon (`'hi'` is "invalid string
   delimiter"); single-quote chars like `'a'` do not exist
   (`41X` hex form does).

Ulm facts confirmed by probe: case-insensitive, `CASE` with `|`
and `ELSE`, `LOOP`/`EXIT`, `RETURN` with value, `&`/`~`, `IN`,
`WITH` guarded-pointer only, declaration order enforced
(`ulmo` rejects `VAR` after procedures — the validator stays
order-free, documented leniency), filenames must match module
names, backend assertion crashes are ignored (frontend-only rule).

## Build

```sh
./build.sh        # -> build/Ulm (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 (Ulm vs `ulmo`, frontend)

Accept battery (15 cases: all statements, `CASE`/`ELSE`, `LOOP`/
`EXIT`, `ORD`, floats, `RETURN`) + `tests/deep.mod` (records,
pointers, multi-dim arrays, nested routines, guarded `WITH`):
**0 false positives**. Broken mutants (8): **0 missed**, positions
close. (`i := 1` without `;` is accepted by `ulmo` too — separator
leniency, correctly skipped.)