# Step: language polish — enum literals + string equality

Tag `v3-lang-polish`. Suite **124/124**; fixpoint **OK**
(`bootstrap/fixpoint.sh`, image **2,070,109 bytes**).

## Enumerations usable everywhere

Previously an enumeration declaration parsed but *use* of any literal
was error 230. Now:

- `Enum` assigns each literal an ordinal `0, 1, …`
  (`QbeGen.IntStr` → `SymTab.SetSymVal`) at declaration.
- `Design`'s constant branch accepts `ClEnum` and yields the ordinal
  as an immediate (`GetSymVal` + `IsImm`).
- `VAR`/parameter declarations accept `ClEnum`; a designator of enum
  type loads/stores as a `w`.
- Works in expressions, `=`/`#`/ordinal comparisons, `CASE` labels
  (labels are immediates), `CONST` initialisers, and as a
  value/parameter type (`PROCEDURE Name(c : Color)`).
- `OrdCheck`/`EqCheck` already required the *same* enum type
  (no mixing distinct enums).

## String equality `=` / `#`

- `SymTab.IsStrType`/`StrCompat`: a string literal (`ClStr`) or a 1-D
  `ARRAY OF CHAR` is a "string" operand.
- `EqCheck` now accepts two string-compatible operands (content
  equality); `OrdCheck` (`<` `<=` `>` `>=`) still rejects strings
  (213).
- `QbeGen.StrEq` emits `%t =w call $m2streq(l a, l b)`, negated with
  `xor 1` for `#`.
- `shim.c`: `m2streq(a, b)` — `strcmp` of the NUL-terminated contents.

## Tests

- `t_enum.mod` (exit 15): literal in comparison, `CONST`, CASE label,
  value parameter, ordinal ordering.
- `t_enumdecl.mod`: was `expect_fail "not supported yet"`; now a run
  test (exit 0).
- `t_streq.mod` (exit 15): `ARRAY OF CHAR` vs literal, literal vs
  literal, `=` and `#` (linked with the shim).

## Still open (polish / next)

- String concatenation `+`, `LEN`.
- Strict `231` def/impl signature checks (types, not just arity).
- `UString` whole-string assignment to a fixed array.
- `ProgramArgs` / `IOChan` (shim `m2argc`/`m2arg` already exist).

## Files

`compiler/src/M2.atg` (`Enum` ordinals; `KindConst`/`VarDecl`/`Design`
`ClEnum`; the `StrCompat` branch in the rel codegen),
`compiler/src/SymTab.def`/`.mod` (`IsStrType`/`StrCompat`, `EqCheck`),
`compiler/src/QbeGen.def`/`.mod` (`StrEq`),
`runtime/syslib/shim.c` (`m2streq`), `compiler/run_tests.sh`,
`compiler/tests/{t_enum,t_enumdecl,t_streq}.mod`,
`docs/features.md`.