# V3 step 3.3 — sets: multi-word masks, full expressions, all ops (done 2026-09-20)

Suite 50/50 (21 run — incl. 3 trap-aborts — + 29 reject).
LL(1)-clean (only the known-benign TypeBlock warning).

## Model (locked: multi-word, full expressions, all ops + IN)

Sets are memory addresses (globals or `alloc8` temps), never
scalars — uniform with arrays. No header (size is static);
W words of bitmask, bit `v-lo`. Unrolled straight-line word code
everywhere (counts static, deterministic).

## Grammar (`M2.atg`)

- `SetType`: `SET OF` bool/char/bounded-subrange (span ≤ 256);
  enums wait for ordinals, `INTEGER` is unbounded → 230.
- `SetLit`/`SetElem` in `Fact`: literals are `SET OF [0..255]`
  (8 words); elements int/char/bool, folded values checked
  0..255 statically (222), computed values trap via `SetBit`;
  ranges always lower via `SetRange` (literals validated, inverted
  runtime ranges are naturally empty, like `FOR 5 TO 1`).
- `+ - * /` branch to union/difference/intersection/symdiff when
  both sides are sets (result spans max, typed exactly so
  downstream word counts match allocations); `IN` added to `Rel`
  (mismatch → 222); set `=`/`#` via word-wise `CmpSet`; `CASE`
  labels reject sets (arrays/strings already 213 themselves).
- `Assign` copies sets (`CopySet` with dst/span word counts).

## Backend (`QbeGen`, all probed first)

`DeclSet`, `NewSetTemp` (`alloc8`, 8-rounded), `SetZero`,
`SetBit`/`SetRange` (span traps), `SetBinOp` (overlap via op,
larger-side extras copied or zeroed), `CmpSet` (min words +
zero-check extras), `CopySet` (min-word `memcpy`, zero-fill,
**trap when src extras beyond dst are nonzero** — narrowing
`{100}` into `SET OF [0..7]` aborts instead of silently
dropping bits), `InSet` (bit test + span trap).
Probe facts reused: `alloc8`, `shr/shl`, strict width checking
(a mixed-width `mul` in the probe failed loudly — hence
`WidenIndex` everywhere).

## SymTab (lenient-by-design, documented)

`SubBounds/SetBase/SetWords/SetBaseLo/SetCount`; `SetBasesOk`
accepts any two suitable bases (masks compare over min words);
`InCheck` accepts small int/char/bool against suitable sets.
Static 222s stay for what is *known* bad (out-of-span literals,
non-sets in `IN`); the runtime trap catches the rest.

## Tests

`t_set` → 131 (all four ops, `IN`, `=`/`#`, empty, var index),
`t_setchar` → 77 (word-3 bits), `t_setrange` → 55 (ranges, var
element, empty compare); `t_bad_setelem`/`t_bad_in` → 222,
`t_bad_setbase` → 230; `t_trap_setspan` → abort (rc=134).

Deferred: enum bases (ordinals), string `=`/`+`, multi-word
performance (unrolled is fine for now), `CHAR`-bound subtleties.