# m2comp step 6 — WITH + CASE (tag: `m2comp-step6`)

Statement-level gap closed with v1 lowering recipes, ported to the
tree-walking backend: `WITH` opens a record scope (bare fields,
nesting, any record designator incl. `a[i]`), `CASE` lowers to
compare-chains over int/char selectors (ranges, multi-labels,
`ELSE`). Suite 61/61 (56 inherited + 2 run + 3 reject); new
keywords `WITH`/`CASE`/`|` (token numbers shifted, `Msg`
regenerated, no test depends on numbers).

## What was built

- `src/AST`: `nkWith` (record designator + stmts), `nkCase`
  (selector + arm chain + else), `nkCaseArm` (label chain + body),
  `nkRange` (`num` = lo, `op` = hi, both folded) + constructors
  and `KindName` entries.
- Grammar: `WithStat` (record check 215, `PushRecord`/`PopScope`
  around the body), `CaseStat` (ordinal selector check 213,
  `EqCheck` per label, `ConstFold` per bound with 230 on
  non-constant, ranges via `..`), wired into `Stat`.
- `src/SymTab`: `ConstFold` accepts `nkChar` (char labels and
  char bounds; no other change needed — `PushRecord` and `EqCheck`
  already existed for this).
- `src/MGen`: WITH address-temp stack (`withTmps`/`withTyps`,
  max 8, reset per module); `EmitWith` evaluates any record
  designator once; bare WITH-fields (`aux = KindField`, no tag)
  resolve in load/address paths via top-down search (stores flow
  through the generic address path); `EmitCase` evaluates the
  selector once and emits per-label `Eq` (ranges: `Ge`+`Le`+`And`)
  `Jz`-chains into arm bodies.
- `run_tests.sh`: `expect_fail` gained an optional `.LST`
  message argument (existing single-arg calls unchanged).

## Tests — 61/61

`t_with` 51 (fields, nested WITH, `a[i]` argument);
`t_case` 138 (multi-labels, `4..6` range, `ELSE`, char
selector, fallthrough-free arms). Rejections: WITH on INTEGER
(215), record selector (213), variable label (230).

## Bugs found (all fixed, all covered)

- None in the compiler: the three rejections "aborted" only
  inside the suite because the new test lines passed bare
  filenames to `expect_fail` (it takes `tests/`-prefixed paths),
  so the driver `HALT`ed on "Could not open input file". Fixed
  the lines; no compiler change.