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summary_step8.md

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Step 8 — VAR actuals with tails (uncommitted)

127/127 tests green (120 + 5 run + 2 rejection; v_bad_var repurposed), mc64 boot + example green, Showcase still 157.

Goal

Accept a[i], p^ and record fields as VAR actuals (error 233 since step 4), using the dormant scaffolding (ActIsVarNext, per-actual frame slots). Keep every old suite green with zero behavior change outside VAR-want position.

What was built

  • MGen: ActFrame.addrs[] (per-actual stashed address temp, -1 when unused); StashAddr (DUP + temp-store at the Fact tail, where the address is complete but not yet loaded — uniform for [], ^ and . tails); ClrStash (invalidates on any value-combining action); ActValue takes the stashed address for VAR formals (address already on top for whole array/record actuals, else drop value + reload stash).
  • M2c.atg: Fact tail stashes when tailed + ActIsVarNext() + head is Var/Param/VarPar/Field + head is not a module + final type is not CHAR/BOOLEAN; ClrStash() at every combining site (Rel/AddOp/MulOp actions, unary neg, NOT, literals, HIGH, call results, set elements).
  • run_tests.sh: step-8 sections added.

Tests — 127/127 (120 + 5 + 2)

5 run: v_idx 35 (a[2], a[4]), v_deref 105 (p^.val), v_field 1031 (r.b.v), v_rec 16 (whole r.b to VAR record formal), v_row 21 (matrix rows to VAR open-array formal). 3 rejections, each exactly one error: v_bad_var 233 (repurposed: P(a[i]+1) — operators defeat the stash), v_bad_byte 233 (CHAR elements are byte-packed, no valid slot address), v_bad_with 233 (WITH-field actuals). Bonus finding: row-to-VAR-open works, free of charge.

Bugs found and fixed

  1. Stale-stash accept: P(a[i]+1) first compiled (stash from a[i]) because nothing invalidated the address when +1 followed. Every value-combining action now calls ClrStash(); direction of error is safe (a missed site would only cause a loud 233, and the audit covered all Fact alternatives, all operator loops, NOT, HIGH, call results and set elements; parens stay transparent).

Known limits (deferred)

WITH-field VAR actuals (233), CHAR/BOOLEAN elements or fields as VAR actuals (233, byte-packing), module vars as VAR actuals (233), type exports, DEFINITION/IMPLEMENTATION split, module BEGIN bodies.