DEFINITION MODULE SymTab;
(* Symbol table with static type checking for SimpleMod2
   (simplified Modula-2 without procedures).

   - flat scopes with levels: globals at level 0, WITH statement
     bodies push the record's fields as an inner scope (shadowing
     allowed, duplicates within one level rejected)
   - every symbol carries a type descriptor index (InvalidType if
     unknown, e.g. imported names); unknown types suppress follow-on
     errors to avoid cascades
   - type descriptors: aliases (one per TYPE declaration, so
     self-references such as POINTER TO Person resolve), subranges,
     enumerations, arrays, records (with field lists), sets,
     pointers, predefined types, string literals
   - INTEGER, CARDINAL and subranges thereof form one lenient
     "integer family"; mixed INTEGER/REAL arithmetic is rejected *)

CONST
  MaxSyms = 256;
  InvalidType = -1;

  (* symbol kinds *)
  KindConst  = 0;
  KindType   = 1;
  KindVar    = 2;
  KindImport = 3;
  KindModule = 4;
  KindPredef = 5;
  KindField  = 6;

  (* type classes returned by ClassOf *)
  ClInvalid = 0;
  ClInt     = 1;
  ClReal    = 2;
  ClChar    = 3;
  ClBool    = 4;
  ClEnum    = 5;
  ClArray   = 6;
  ClRecord  = 7;
  ClSet     = 8;
  ClPtr     = 9;
  ClStr     = 10;

  (* operator codes for RelCheck *)
  OpEq = 0; OpNeq1 = 1; OpNeq2 = 2;
  OpLt = 3; OpLe  = 4; OpGt   = 5; OpGe = 6;
  OpIn = 7;
  (* operator codes for AddOp / MulOp *)
  OpAdd = 0; OpSub = 1; OpOr = 2;
  OpTimes = 0; OpSlash = 1; OpDiv = 2; OpMod = 3; OpAnd = 4;

TYPE
  Name = ARRAY [0 .. 63] OF CHAR;
  TypeIndex = INTEGER;

(* ---------------- symbols and scopes ---------------- *)

PROCEDURE Init;
(* Clears the table and enters predefined identifiers
   (INTEGER, CARDINAL, SHORTINT, LONGINT, REAL, LONGREAL, CHAR,
   BOOLEAN, TRUE, FALSE, NIL). *)

PROCEDURE Enter (name: ARRAY OF CHAR; kind: INTEGER): BOOLEAN;
(* Enters name at the current scope level (type InvalidType).
   Returns FALSE on duplicate within the same level. *)

PROCEDURE EnterPending (name: ARRAY OF CHAR; kind: INTEGER): BOOLEAN;
(* Like Enter, but remembers the entry for a later FixPending call
   (used for VAR identifier lists whose type is parsed afterwards).
   Returns FALSE on duplicate (entry not recorded). *)

PROCEDURE FixPending (t: TypeIndex);
(* Assigns type t to all pending entries, clears the buffer. *)

PROCEDURE PendCount (): CARDINAL;
(* Number of entries currently waiting for FixPending. *)

PROCEDURE PendName (i: CARDINAL; VAR n: Name);
(* Name of the i-th pending entry (empty string if out of range).
   Used by the QBE backend to emit storage for VAR lists whose
   type is parsed after the identifiers. *)

PROCEDURE FieldPending (rec: TypeIndex; name: ARRAY OF CHAR): BOOLEAN;
(* Records a field name for record descriptor rec (type fixed later
   with FixPendingF). Returns FALSE on duplicate field. *)

PROCEDURE FixPendingF (rec: TypeIndex; t: TypeIndex);
(* Assigns type t to pending fields owned by rec. *)

PROCEDURE Lookup (name: ARRAY OF CHAR): BOOLEAN;
(* TRUE if name is visible (innermost scope wins). *)

PROCEDURE SymType (name: ARRAY OF CHAR): TypeIndex;
(* Type of innermost visible entry, InvalidType if absent. *)

PROCEDURE SetSymType (name: ARRAY OF CHAR; t: TypeIndex);
(* Sets type of innermost visible entry. *)

PROCEDURE SymKind (name: ARRAY OF CHAR): INTEGER;
(* Kind of innermost visible entry, -1 if absent. *)

PROCEDURE Equal (a, b: ARRAY OF CHAR): BOOLEAN;

PROCEDURE PushScope;
PROCEDURE PopScope;
(* WITH statement support: PushRecord pushes a record's fields. *)

PROCEDURE PushRecord (t: TypeIndex): BOOLEAN;
(* Pushes a scope containing t's fields (as KindField). FALSE if t
   is not a record type (or invalid). Caller must PopScope after. *)

PROCEDURE PrintTable;

(* ---------------- type descriptors ---------------- *)

PROCEDURE NewAlias (): TypeIndex;
PROCEDURE NewSub (base: TypeIndex): TypeIndex;
PROCEDURE NewEnum (): TypeIndex;
PROCEDURE NewArray (elem: TypeIndex): TypeIndex;
PROCEDURE NewRecord (): TypeIndex;
PROCEDURE NewSet (base: TypeIndex): TypeIndex;
PROCEDURE NewPtr (base: TypeIndex): TypeIndex;
PROCEDURE NewStr (): TypeIndex;
(* Fresh descriptors; base/elem may be InvalidType. InvalidType is
   returned when the table is full. *)

PROCEDURE SetTarget (t, base: TypeIndex);
(* Sets an alias target (TYPE declaration completion). *)

PROCEDURE IntType (): TypeIndex;
PROCEDURE RealType (): TypeIndex;
PROCEDURE CharType (): TypeIndex;
PROCEDURE BoolType (): TypeIndex;

PROCEDURE ClassOf (t: TypeIndex): INTEGER;
(* Resolves aliases; InvalidType maps to ClInvalid. *)

PROCEDURE IsIntFamily (t: TypeIndex): BOOLEAN;
(* INTEGER, CARDINAL or subrange thereof (Invalid suppresses). *)

PROCEDURE SameType (a, b: TypeIndex): BOOLEAN;
(* Same resolved descriptor (Invalid suppresses). *)

PROCEDURE FieldExists (rec: TypeIndex; name: ARRAY OF CHAR): BOOLEAN;
PROCEDURE FieldType (rec: TypeIndex; name: ARRAY OF CHAR): TypeIndex;
PROCEDURE ArrayElem (t: TypeIndex): TypeIndex;
PROCEDURE PtrBase (t: TypeIndex): TypeIndex;

(* ---------------- predicates used by grammar checks ---------------- *)
(* All return TRUE if either operand is InvalidType (no cascades). *)

PROCEDURE Assignable (src, dst: TypeIndex): BOOLEAN;
(* Assignment compatibility (210). *)

PROCEDURE ArithCheck (l, r: TypeIndex; divmod: BOOLEAN;
                      VAR res: TypeIndex): BOOLEAN;
(* + - * / (divmod FALSE) or DIV MOD (TRUE); res is result type (211). *)

PROCEDURE UnaryCheck (t: TypeIndex; VAR res: TypeIndex): BOOLEAN;
(* Unary + - (part of 211). *)

PROCEDURE BoolCheck (t: TypeIndex): BOOLEAN;
(* BOOLEAN required: NOT/AND/OR operands (212), conditions (214). *)

PROCEDURE RelCheck (l, r: TypeIndex; op: INTEGER): BOOLEAN;
(* = # <> < <= > >= IN (213/222 chosen by caller via op). *)

PROCEDURE EqCheck (l, r: TypeIndex): BOOLEAN;
(* = # compatibility, also reused for CASE label matching. *)

PROCEDURE InCheck (l, set: TypeIndex): BOOLEAN;
PROCEDURE SetElemCheck (first, elem: TypeIndex): BOOLEAN;
PROCEDURE SetFor (elem: TypeIndex): TypeIndex;
(* Fresh SET OF elem descriptor for set literals. *)

PROCEDURE StrLen (s: ARRAY OF CHAR): CARDINAL;

END SymTab.