Add symbol table with scope nesting and built-in types

TSymbolTable manages a scope stack with case-insensitive lookup. Each TScope holds a sorted TStringList (names → TSymbol) and chains to its parent for identifier resolution. Built-in primitives (Integer, Int64, UInt32, Byte, Boolean, string) and I/O procedures (Write, WriteLn) are pre-registered in the global scope. 29 FPCUnit tests, all passing.
2026-04-20 17:52:09 +01:00 · 2026-04-20 17:52:09 +01:00 · a561525ebd
parent 95e1ea58af
commit a561525ebd
3 changed files with 869 additions and 1 deletions
--- a/compiler/src/main/pascal/uSymbolTable.pas
+++ b/compiler/src/main/pascal/uSymbolTable.pas
@ -0,0 +1,335 @@
+unit uSymbolTable;
+
+{$mode objfpc}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, contnrs;
+
+type
+  { ------------------------------------------------------------------ }
+  {  Type descriptors                                                   }
+  { ------------------------------------------------------------------ }
+
+  TTypeKind = (
+    tyInteger,    { Int32  — QBE 'w' }
+    tyInt64,      { Int64  — QBE 'l' }
+    tyUInt32,     { UInt32 — QBE 'w' unsigned }
+    tyByte,       { Byte   — QBE 'b' }
+    tyBoolean,    { Boolean — stored as byte, 0/1 only }
+    tyString,     { ARC-managed UTF-8 string }
+    tyRecord,     { Stack-allocated aggregate (Phase 2) }
+    tyClass,      { Heap-allocated, single-inheritance (Phase 2) }
+    tyVoid        { No value — used as procedure return type }
+  );
+
+  TTypeDesc = class
+  public
+    Kind: TTypeKind;
+    Name: string;
+    function IsNumeric: Boolean;
+    function IsString: Boolean;
+    function IsOrdinal: Boolean;
+  end;
+
+  { ------------------------------------------------------------------ }
+  {  Symbols                                                            }
+  { ------------------------------------------------------------------ }
+
+  TSymbolKind = (
+    skVariable,
+    skType,
+    skProcedure,
+    skFunction,
+    skParameter
+  );
+
+  TParamDesc = class
+  public
+    Name:     string;
+    TypeDesc: TTypeDesc;  { not owned }
+    IsConst:  Boolean;
+    IsVar:    Boolean;
+  end;
+
+  TSymbol = class
+  public
+    Name:     string;
+    Kind:     TSymbolKind;
+    TypeDesc: TTypeDesc;    { not owned; nil for procedures }
+    Params:   TObjectList;  { owned TParamDesc; populated for procedures/functions }
+    constructor Create(const AName: string; AKind: TSymbolKind; AType: TTypeDesc);
+    destructor Destroy; override;
+  end;
+
+  { ------------------------------------------------------------------ }
+  {  Scope                                                              }
+  { ------------------------------------------------------------------ }
+
+  TScope = class
+  private
+    FParent:  TScope;
+    FSymbols: TObjectList;  { owns all TSymbol in this scope }
+    FKeys:    TStringList;  { sorted, case-insensitive; Objects[] = TSymbol (not owned) }
+  public
+    constructor Create(AParent: TScope);
+    destructor Destroy; override;
+    property Parent: TScope read FParent;
+    { Returns False if name already defined in this scope; caller must free ASymbol. }
+    function Define(ASymbol: TSymbol): Boolean;
+    function LookupLocal(const AName: string): TSymbol;
+    function Lookup(const AName: string): TSymbol;
+  end;
+
+  { ------------------------------------------------------------------ }
+  {  Symbol table                                                       }
+  { ------------------------------------------------------------------ }
+
+  TSymbolTable = class
+  private
+    FScopeStack: TObjectList;   { owned TScope, index 0 = global }
+    FAllTypes:   TObjectList;   { owned TTypeDesc }
+
+    FTypeInteger: TTypeDesc;
+    FTypeInt64:   TTypeDesc;
+    FTypeUInt32:  TTypeDesc;
+    FTypeByte:    TTypeDesc;
+    FTypeBoolean: TTypeDesc;
+    FTypeString:  TTypeDesc;
+    FTypeVoid:    TTypeDesc;
+
+    function GetCurrentScope: TScope;
+    function GetScopeDepth: Integer;
+    function NewType(AKind: TTypeKind; const AName: string): TTypeDesc;
+    procedure RegisterBuiltins;
+  public
+    constructor Create;
+    destructor Destroy; override;
+
+    { Scope management }
+    function  PushScope: TScope;
+    procedure PopScope;
+    property  CurrentScope: TScope read GetCurrentScope;
+    property  ScopeDepth: Integer read GetScopeDepth;
+
+    { Symbol management — owns ASymbol on success; caller must free on False }
+    function Define(ASymbol: TSymbol): Boolean;
+    function Lookup(const AName: string): TSymbol;
+
+    { Type lookup — case-insensitive, returns nil if not found }
+    function FindType(const AName: string): TTypeDesc;
+
+    { Convenience type accessors }
+    property TypeInteger: TTypeDesc read FTypeInteger;
+    property TypeInt64:   TTypeDesc read FTypeInt64;
+    property TypeUInt32:  TTypeDesc read FTypeUInt32;
+    property TypeByte:    TTypeDesc read FTypeByte;
+    property TypeBoolean: TTypeDesc read FTypeBoolean;
+    property TypeString:  TTypeDesc read FTypeString;
+    property TypeVoid:    TTypeDesc read FTypeVoid;
+  end;
+
+implementation
+
+{ ------------------------------------------------------------------ }
+{ TTypeDesc                                                           }
+{ ------------------------------------------------------------------ }
+
+function TTypeDesc.IsNumeric: Boolean;
+begin
+  Result := Kind in [tyInteger, tyInt64, tyUInt32, tyByte];
+end;
+
+function TTypeDesc.IsString: Boolean;
+begin
+  Result := Kind = tyString;
+end;
+
+function TTypeDesc.IsOrdinal: Boolean;
+begin
+  Result := Kind in [tyInteger, tyInt64, tyUInt32, tyByte, tyBoolean];
+end;
+
+{ ------------------------------------------------------------------ }
+{ TSymbol                                                             }
+{ ------------------------------------------------------------------ }
+
+constructor TSymbol.Create(const AName: string; AKind: TSymbolKind; AType: TTypeDesc);
+begin
+  inherited Create;
+  Name     := AName;
+  Kind     := AKind;
+  TypeDesc := AType;
+  Params   := TObjectList.Create(True);
+end;
+
+destructor TSymbol.Destroy;
+begin
+  Params.Free;
+  inherited Destroy;
+end;
+
+{ ------------------------------------------------------------------ }
+{ TScope                                                              }
+{ ------------------------------------------------------------------ }
+
+constructor TScope.Create(AParent: TScope);
+begin
+  inherited Create;
+  FParent  := AParent;
+  FSymbols := TObjectList.Create(True);
+  FKeys    := TStringList.Create;
+  FKeys.Sorted        := True;
+  FKeys.CaseSensitive := False;
+  FKeys.Duplicates    := dupIgnore;  { we check manually before inserting }
+end;
+
+destructor TScope.Destroy;
+begin
+  FKeys.Free;
+  FSymbols.Free;
+  inherited Destroy;
+end;
+
+function TScope.Define(ASymbol: TSymbol): Boolean;
+var
+  Idx: Integer;
+begin
+  if FKeys.Find(ASymbol.Name, Idx) then
+  begin
+    Result := False;
+    Exit;
+  end;
+  FSymbols.Add(ASymbol);
+  { Store the TSymbol pointer directly in the string list's Objects slot. }
+  FKeys.AddObject(ASymbol.Name, ASymbol);
+  Result := True;
+end;
+
+function TScope.LookupLocal(const AName: string): TSymbol;
+var
+  Idx: Integer;
+begin
+  if FKeys.Find(AName, Idx) then
+    Result := TSymbol(FKeys.Objects[Idx])
+  else
+    Result := nil;
+end;
+
+function TScope.Lookup(const AName: string): TSymbol;
+var
+  S: TScope;
+begin
+  S := Self;
+  while S <> nil do
+  begin
+    Result := S.LookupLocal(AName);
+    if Result <> nil then
+      Exit;
+    S := S.FParent;
+  end;
+  Result := nil;
+end;
+
+{ ------------------------------------------------------------------ }
+{ TSymbolTable                                                        }
+{ ------------------------------------------------------------------ }
+
+constructor TSymbolTable.Create;
+begin
+  inherited Create;
+  FScopeStack := TObjectList.Create(True);
+  FAllTypes   := TObjectList.Create(True);
+  { Global scope — parent = nil }
+  FScopeStack.Add(TScope.Create(nil));
+  RegisterBuiltins;
+end;
+
+destructor TSymbolTable.Destroy;
+begin
+  FScopeStack.Free;
+  FAllTypes.Free;
+  inherited Destroy;
+end;
+
+function TSymbolTable.NewType(AKind: TTypeKind; const AName: string): TTypeDesc;
+begin
+  Result      := TTypeDesc.Create;
+  Result.Kind := AKind;
+  Result.Name := AName;
+  FAllTypes.Add(Result);
+end;
+
+procedure TSymbolTable.RegisterBuiltins;
+var
+  Sym: TSymbol;
+begin
+  { Primitive types }
+  FTypeInteger := NewType(tyInteger, 'Integer');
+  FTypeInt64   := NewType(tyInt64,   'Int64');
+  FTypeUInt32  := NewType(tyUInt32,  'UInt32');
+  FTypeByte    := NewType(tyByte,    'Byte');
+  FTypeBoolean := NewType(tyBoolean, 'Boolean');
+  FTypeString  := NewType(tyString,  'string');
+  FTypeVoid    := NewType(tyVoid,    'void');
+
+  { Register type names as skType symbols in global scope }
+  Define(TSymbol.Create('Integer', skType, FTypeInteger));
+  Define(TSymbol.Create('Int64',   skType, FTypeInt64));
+  Define(TSymbol.Create('UInt32',  skType, FTypeUInt32));
+  Define(TSymbol.Create('Byte',    skType, FTypeByte));
+  Define(TSymbol.Create('Boolean', skType, FTypeBoolean));
+  Define(TSymbol.Create('string',  skType, FTypeString));
+
+  { Built-in I/O procedures }
+  Sym := TSymbol.Create('Write',   skProcedure, nil);
+  Define(Sym);
+  Sym := TSymbol.Create('WriteLn', skProcedure, nil);
+  Define(Sym);
+end;
+
+function TSymbolTable.GetCurrentScope: TScope;
+begin
+  Result := TScope(FScopeStack[FScopeStack.Count - 1]);
+end;
+
+function TSymbolTable.GetScopeDepth: Integer;
+begin
+  Result := FScopeStack.Count;
+end;
+
+function TSymbolTable.PushScope: TScope;
+begin
+  Result := TScope.Create(CurrentScope);
+  FScopeStack.Add(Result);
+end;
+
+procedure TSymbolTable.PopScope;
+begin
+  if FScopeStack.Count > 1 then
+    FScopeStack.Delete(FScopeStack.Count - 1);
+end;
+
+function TSymbolTable.Define(ASymbol: TSymbol): Boolean;
+begin
+  Result := CurrentScope.Define(ASymbol);
+end;
+
+function TSymbolTable.Lookup(const AName: string): TSymbol;
+begin
+  Result := CurrentScope.Lookup(AName);
+end;
+
+function TSymbolTable.FindType(const AName: string): TTypeDesc;
+var
+  Sym: TSymbol;
+begin
+  Sym := CurrentScope.Lookup(AName);
+  if (Sym <> nil) and (Sym.Kind = skType) then
+    Result := Sym.TypeDesc
+  else
+    Result := nil;
+end;
+
+end.
--- a/compiler/src/test/pascal/TestRunner.pas
+++ b/compiler/src/test/pascal/TestRunner.pas
@ -12,7 +12,8 @@ uses
  consoletestrunner,
  cp.test.lexer,
  cp.test.parser,
-  cp.test.codegen;
+  cp.test.codegen,
+  cp.test.symtable;

 var
  Application: TTestRunner;
--- a/compiler/src/test/pascal/cp.test.symtable.pas
+++ b/compiler/src/test/pascal/cp.test.symtable.pas
@ -0,0 +1,532 @@
+unit cp.test.symtable;
+
+{$mode objfpc}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, fpcunit, testregistry,
+  uSymbolTable;
+
+type
+  TSymbolTableTests = class(TTestCase)
+  published
+    { Built-in primitive types are pre-registered }
+    procedure TestBuiltin_Type_Integer;
+    procedure TestBuiltin_Type_Int64;
+    procedure TestBuiltin_Type_UInt32;
+    procedure TestBuiltin_Type_Byte;
+    procedure TestBuiltin_Type_Boolean;
+    procedure TestBuiltin_Type_String;
+
+    { Type descriptor properties }
+    procedure TestTypeDesc_Integer_IsNumeric;
+    procedure TestTypeDesc_Boolean_IsNotNumeric;
+    procedure TestTypeDesc_String_IsString;
+    procedure TestTypeDesc_Integer_IsNotString;
+
+    { FindType is case-insensitive (Pascal identifiers are) }
+    procedure TestFindType_CaseInsensitive;
+    procedure TestFindType_Unknown_ReturnsNil;
+
+    { Symbol definition }
+    procedure TestDefine_Variable;
+    procedure TestDefine_Procedure;
+    procedure TestDefine_DuplicateInSameScope_ReturnsFalse;
+    procedure TestDefine_SameNameDiffScope_IsAllowed;
+
+    { Symbol lookup }
+    procedure TestLookup_FindsInCurrentScope;
+    procedure TestLookup_NotFound_ReturnsNil;
+    procedure TestLookup_CaseInsensitive;
+
+    { Scope nesting }
+    procedure TestScope_InnerSeesOuter;
+    procedure TestScope_OuterCannotSeeInner;
+    procedure TestScope_InnerShadowsOuter;
+    procedure TestScope_AfterPop_InnerSymbolsGone;
+    procedure TestScope_DepthAfterPushPop;
+
+    { Built-in procedures }
+    procedure TestBuiltin_WriteLn_Exists;
+    procedure TestBuiltin_Write_Exists;
+    procedure TestBuiltin_WriteLn_IsProcedure;
+
+    { Symbol properties }
+    procedure TestSymbol_Variable_HasType;
+    procedure TestSymbol_Procedure_HasVoidReturn;
+  end;
+
+implementation
+
+{ ------------------------------------------------------------------ }
+{ Helpers                                                             }
+{ ------------------------------------------------------------------ }
+
+function MakeVar(const AName: string; AType: TTypeDesc): TSymbol;
+begin
+  Result := TSymbol.Create(AName, skVariable, AType);
+end;
+
+function MakeProc(const AName: string): TSymbol;
+begin
+  Result := TSymbol.Create(AName, skProcedure, nil);
+end;
+
+{ ------------------------------------------------------------------ }
+{ Built-in types                                                      }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestBuiltin_Type_Integer;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('Integer type', ST.FindType('Integer'));
+    AssertEquals('Integer kind', Ord(tyInteger), Ord(ST.FindType('Integer').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_Type_Int64;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('Int64 type', ST.FindType('Int64'));
+    AssertEquals('Int64 kind', Ord(tyInt64), Ord(ST.FindType('Int64').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_Type_UInt32;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('UInt32 type', ST.FindType('UInt32'));
+    AssertEquals('UInt32 kind', Ord(tyUInt32), Ord(ST.FindType('UInt32').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_Type_Byte;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('Byte type', ST.FindType('Byte'));
+    AssertEquals('Byte kind', Ord(tyByte), Ord(ST.FindType('Byte').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_Type_Boolean;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('Boolean type', ST.FindType('Boolean'));
+    AssertEquals('Boolean kind', Ord(tyBoolean), Ord(ST.FindType('Boolean').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_Type_String;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('string type', ST.FindType('string'));
+    AssertEquals('string kind', Ord(tyString), Ord(ST.FindType('string').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ Type descriptor properties                                          }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestTypeDesc_Integer_IsNumeric;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertTrue('Integer is numeric', ST.FindType('Integer').IsNumeric);
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestTypeDesc_Boolean_IsNotNumeric;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertFalse('Boolean is not numeric', ST.FindType('Boolean').IsNumeric);
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestTypeDesc_String_IsString;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertTrue('string IsString', ST.FindType('string').IsString);
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestTypeDesc_Integer_IsNotString;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertFalse('Integer IsString', ST.FindType('Integer').IsString);
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ FindType                                                            }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestFindType_CaseInsensitive;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('integer lowercase', ST.FindType('integer'));
+    AssertNotNull('INTEGER uppercase', ST.FindType('INTEGER'));
+    AssertNotNull('String mixed',      ST.FindType('String'));
+    AssertSame('Same descriptor', ST.FindType('Integer'), ST.FindType('integer'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestFindType_Unknown_ReturnsNil;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNull('unknown type', ST.FindType('Foobar'));
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ Symbol definition                                                   }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestDefine_Variable;
+var
+  ST:  TSymbolTable;
+  Sym: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Sym := MakeVar('x', ST.FindType('Integer'));
+    AssertTrue('Define succeeds', ST.Define(Sym));
+    AssertSame('Lookup finds it', Sym, ST.Lookup('x'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestDefine_Procedure;
+var
+  ST:  TSymbolTable;
+  Sym: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Sym := MakeProc('Greet');
+    AssertTrue('Define succeeds', ST.Define(Sym));
+    AssertEquals('Kind', Ord(skProcedure), Ord(ST.Lookup('Greet').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestDefine_DuplicateInSameScope_ReturnsFalse;
+var
+  ST: TSymbolTable;
+  S1, S2: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    S1 := MakeVar('x', ST.FindType('Integer'));
+    S2 := MakeVar('x', ST.FindType('string'));
+    AssertTrue('First define ok', ST.Define(S1));
+    AssertFalse('Duplicate fails', ST.Define(S2));
+    S2.Free;
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestDefine_SameNameDiffScope_IsAllowed;
+var
+  ST: TSymbolTable;
+  S1, S2: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    S1 := MakeVar('n', ST.FindType('Integer'));
+    AssertTrue('Outer define ok', ST.Define(S1));
+    ST.PushScope;
+    S2 := MakeVar('n', ST.FindType('string'));
+    AssertTrue('Inner define ok — shadowing allowed', ST.Define(S2));
+    ST.PopScope;
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ Symbol lookup                                                       }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestLookup_FindsInCurrentScope;
+var
+  ST:  TSymbolTable;
+  Sym: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Sym := MakeVar('result', ST.FindType('Integer'));
+    ST.Define(Sym);
+    AssertSame('Found', Sym, ST.Lookup('result'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestLookup_NotFound_ReturnsNil;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNull('Missing symbol', ST.Lookup('doesNotExist'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestLookup_CaseInsensitive;
+var
+  ST:  TSymbolTable;
+  Sym: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Sym := MakeVar('MyVar', ST.FindType('Integer'));
+    ST.Define(Sym);
+    AssertSame('lowercase', Sym, ST.Lookup('myvar'));
+    AssertSame('uppercase', Sym, ST.Lookup('MYVAR'));
+    AssertSame('mixed',     Sym, ST.Lookup('MyVar'));
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ Scope nesting                                                       }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestScope_InnerSeesOuter;
+var
+  ST:    TSymbolTable;
+  Outer: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Outer := MakeVar('x', ST.FindType('Integer'));
+    ST.Define(Outer);
+    ST.PushScope;
+    AssertSame('Inner sees outer x', Outer, ST.Lookup('x'));
+    ST.PopScope;
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestScope_OuterCannotSeeInner;
+var
+  ST:    TSymbolTable;
+  Inner: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    ST.PushScope;
+    Inner := MakeVar('local', ST.FindType('Integer'));
+    ST.Define(Inner);
+    ST.PopScope;
+    AssertNull('Outer cannot see inner local', ST.Lookup('local'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestScope_InnerShadowsOuter;
+var
+  ST:     TSymbolTable;
+  Outer, Inner: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Outer := MakeVar('n', ST.FindType('Integer'));
+    ST.Define(Outer);
+    ST.PushScope;
+    Inner := MakeVar('n', ST.FindType('string'));
+    ST.Define(Inner);
+    AssertSame('Inner n shadows outer n', Inner, ST.Lookup('n'));
+    ST.PopScope;
+    AssertSame('After pop, outer n visible again', Outer, ST.Lookup('n'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestScope_AfterPop_InnerSymbolsGone;
+var
+  ST:    TSymbolTable;
+  Inner: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    ST.PushScope;
+    Inner := MakeVar('temp', ST.FindType('Integer'));
+    ST.Define(Inner);
+    AssertNotNull('Present before pop', ST.Lookup('temp'));
+    ST.PopScope;
+    AssertNull('Gone after pop', ST.Lookup('temp'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestScope_DepthAfterPushPop;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertEquals('Depth 1 initially', 1, ST.ScopeDepth);
+    ST.PushScope;
+    AssertEquals('Depth 2 after push', 2, ST.ScopeDepth);
+    ST.PushScope;
+    AssertEquals('Depth 3', 3, ST.ScopeDepth);
+    ST.PopScope;
+    AssertEquals('Depth 2 after pop', 2, ST.ScopeDepth);
+    ST.PopScope;
+    AssertEquals('Depth 1 restored', 1, ST.ScopeDepth);
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ Built-in procedures                                                 }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestBuiltin_WriteLn_Exists;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('WriteLn exists', ST.Lookup('WriteLn'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_Write_Exists;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertNotNull('Write exists', ST.Lookup('Write'));
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestBuiltin_WriteLn_IsProcedure;
+var
+  ST: TSymbolTable;
+begin
+  ST := TSymbolTable.Create;
+  try
+    AssertEquals('WriteLn kind',
+      Ord(skProcedure), Ord(ST.Lookup('WriteLn').Kind));
+  finally
+    ST.Free;
+  end;
+end;
+
+{ ------------------------------------------------------------------ }
+{ Symbol properties                                                   }
+{ ------------------------------------------------------------------ }
+
+procedure TSymbolTableTests.TestSymbol_Variable_HasType;
+var
+  ST:  TSymbolTable;
+  Sym: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Sym := MakeVar('s', ST.FindType('string'));
+    ST.Define(Sym);
+    AssertSame('TypeDesc', ST.FindType('string'), ST.Lookup('s').TypeDesc);
+  finally
+    ST.Free;
+  end;
+end;
+
+procedure TSymbolTableTests.TestSymbol_Procedure_HasVoidReturn;
+var
+  ST:  TSymbolTable;
+  Sym: TSymbol;
+begin
+  ST := TSymbolTable.Create;
+  try
+    Sym := MakeProc('DoSomething');
+    ST.Define(Sym);
+    AssertNull('Procedure has no return type', ST.Lookup('DoSomething').TypeDesc);
+  finally
+    ST.Free;
+  end;
+end;
+
+initialization
+  RegisterTest(TSymbolTableTests);
+
+end.