M2compiler-V3/docs/summary_two-phase-slice3.md

Two-phase refactor — slice 3 (designators → AST)

Branch ast-stage-c. Suite 178/178; self-hosting fixpoint OK (2,970,007 bytes; slice 2 was 2,966,245).

What landed

Design now builds a designator node in addition to emitting, so real expressions (identifiers, indexing, fields, derefs, qualified names) have a meaningful AST, not just literals.

Part	AST
base identifier	NkDesignator with child 0 = NkIdent(name)
[ expr ] / , expr	one NkSelector (SelIndex) per index, child 0 = the index expression
. field	NkSelector (SelField), child 0 = NkIdent(field)
^	NkSelector (SelDeref), no child

Design keeps a per-invocation astDes local; each selector is appended with AST.SetChild(astDes, AST.NChild(astDes), …), and the production ends with astCur := astDes. Fact's designator alternative captures that node right after Design returns (astD := astCur) and, at the end of the alternative, does

IF astCall THEN astCur := AST.NoNode ELSE astCur := astD END;
astIsLit := TRUE

so a bare designator survives the Fact reset, while a brace literal or a call (both marked astCall := TRUE) still yields NoNode for now.

Verified (temporary AST.Dump, then removed)

• a[1] → NkDesignator(Ident a, SelIndex(1))
• r.f → NkDesignator(Ident r, SelField(Ident f))
• p^ → NkDesignator(Ident p, SelDeref)
• r.f + a[2] → Add(NkDesignator(r, SelField f), NkDesignator(a, SelIndex 2))

Two bugs were caught this way:

1. AST.AddChild returns BOOLEAN; GNU Modula-2 refuses to discard a function result. Switched to AST.SetChild(n, AST.NChild(n), …).
2. The field name was first stored as a raw TxtIndex in NkSelector.child[0]. Any tree walk (e.g. AST.Dump) then reads that integer as a node index and can recurse forever — r.f hung the dump. Fixed by storing a real NkIdent node as the child.

Deliberately deferred

Still NoNode in Fact: calls (ArgList), brace/set literals, ResultComp suffixes, builds CHR/ORD/ABS/HIGH/LEN/…, NOT. Lower + .ssa byte-compare still not started.

Next

Slice 4: statements (Block/Stat) build NkAssign/NkIf/NkWhile/…, then calls/braces; or first finish Fact (calls, builtins). Statements are the missing piece before a body can be lowered from the AST.