Wire semantic analysis pass into the compiler pipeline

The semantic analyser now runs between parsing and code generation.
Type mismatches, undeclared identifiers, and duplicate declarations are
reported to stderr with source position and exit code 1 before any IR
is emitted.

compiler/src/main/pascal/Blaise.pas

@@ -16,7 +16,7 @@ program Blaise;
 
 uses
   SysUtils, Classes, Process,
-  uLexer, uParser, uAST, uCodeGenQBE;
+  uLexer, uParser, uAST, uSemantic, uCodeGenQBE;
 
 const
   Version = '0.1.0-alpha';
@@ -272,10 +272,11 @@ var
   SourceFile, OutputFile: string;
   EmitIR: Boolean;
   Source: TStringList;
-  Lexer:  TLexer;
-  Parser: TParser;
-  Prog:   TProgram;
-  CG:     TCodeGenQBE;
+  Lexer:    TLexer;
+  Parser:   TParser;
+  Prog:     TProgram;
+  Semantic: TSemanticAnalyser;
+  CG:       TCodeGenQBE;
   IR:     string;
   IRFile: string;
 
@@ -315,10 +316,11 @@ begin
     end;
   end;
 
-  Lexer  := nil;
-  Parser := nil;
-  Prog   := nil;
-  CG     := nil;
+  Lexer    := nil;
+  Parser   := nil;
+  Prog     := nil;
+  Semantic := nil;
+  CG       := nil;
   try
     try
       Lexer  := TLexer.Create(Source.Text);
@@ -332,6 +334,17 @@ begin
       end;
     end;
 
+    try
+      Semantic := TSemanticAnalyser.Create;
+      Semantic.Analyse(Prog);
+    except
+      on E: ESemanticError do
+      begin
+        WriteLn(StdErr, 'Semantic error: ', E.Message);
+        Halt(1);
+      end;
+    end;
+
     try
       CG := TCodeGenQBE.Create;
       CG.Generate(Prog);
@@ -345,6 +358,7 @@ begin
     end;
   finally
     CG.Free;
+    Semantic.Free;
     Prog.Free;
     Parser.Free;
     Lexer.Free;