DEFINITION MODULE Lower;
(* AST -> QBE walk for the two-phase frontend (docs/plan-lower.md).

   Test-only: after a normal parse has built the AST and emitted the
   legacy image, CanLower gates whether the unit is in the supported
   subset; LowerUnit then re-emits it into a fresh QbeGen state, writing
   gen_ssa/<mod>L.ssa for a byte-compare against the legacy image.

   Symbol resolution is self-contained (zero SymTab surface): the grammar
   records each declaration's kind/type and each procedure's signature in
   the tables below while the scope is open, so the walk can resolve names
   after SymTab has popped their scopes. *)

IMPORT AST, SymTab, QbeGen;

PROCEDURE CanLower (unit: AST.Node): BOOLEAN;
PROCEDURE LowerUnit (unit: AST.Node);
PROCEDURE LowerSession (units: ARRAY OF AST.Node; n: CARDINAL;
                        progName: ARRAY OF CHAR);
PROCEDURE BeginSession (progName: ARRAY OF CHAR);
PROCEDURE BeginUnit;
PROCEDURE LowerUnitNow (unit: AST.Node; isProg: BOOLEAN);
PROCEDURE EndSession;

(* The expression/statement/declaration walkers are mutually recursive.
   gm2's link pass rejects FORWARD and V3 has no whole-module pass, so
   they are declared here (definition-visible throughout the
   implementation) instead of being forward-declared. *)
PROCEDURE CanExpr (n: AST.Node): BOOLEAN;
PROCEDURE CanDecls (seq: AST.Node): BOOLEAN;
PROCEDURE CanProc (proc: AST.Node): BOOLEAN;
PROCEDURE IsBuiltin (nm: ARRAY OF CHAR): BOOLEAN;
PROCEDURE LowerExpr (n: AST.Node; VAR t: SymTab.TypeIndex;
                     VAR q: QbeGen.QVal);
PROCEDURE LowerStmt (seq: AST.Node);
PROCEDURE LowerDecls (seq: AST.Node);

PROCEDURE Reset;
PROCEDURE NoteVar (name: ARRAY OF CHAR; kind: INTEGER; t: SymTab.TypeIndex);
PROCEDURE NoteConstVal (val: ARRAY OF CHAR);
PROCEDURE ScopeEnter;
PROCEDURE ScopeLeave;
PROCEDURE NoteProc (name: ARRAY OF CHAR; uid: CARDINAL;
                    res: SymTab.TypeIndex; depth: CARDINAL; ext: BOOLEAN);
PROCEDURE MarkProcExternal;
PROCEDURE NoteProcNode (n: AST.Node);
PROCEDURE SetProcRes (t: SymTab.TypeIndex);
PROCEDURE NoteParam (name: ARRAY OF CHAR; t: SymTab.TypeIndex;
                     isVar: BOOLEAN);

END Lower.