feat(constants): implement literal constants with lexical scope

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

2 files changed, 35 insertions, 1 deletions

diff --git a/lib/Parser/Parser.cc b/lib/Parser/Parser.cc
index 58422fc..d8fecdc 100644
--- a/lib/Parser/Parser.cc
+++ b/lib/Parser/Parser.cc
@@ -45,7 +45,7 @@ std::vector<std::unique_ptr<StmtAST>> Parser::Parse() {
 void Parser::syncToStatementStart() {
     while (CurTok != tok_eof) {
         switch (CurTok) {
-        case tok_declare: case tok_identifier: case tok_input: case tok_output:
+        case tok_constant: case tok_declare: case tok_identifier: case tok_input: case tok_output:
         case tok_case: case tok_endcase: case tok_otherwise:
         case tok_if: case tok_while: case tok_repeat: case tok_for:
         case tok_function: case tok_procedure: case tok_call: case tok_return:
@@ -98,6 +98,7 @@ std::unique_ptr<StmtAST> Parser::ParseStatementImpl() {
         getNextToken();
         return nullptr;
     }
+    if (CurTok == tok_constant) return ParseConstant();
     if (CurTok == tok_declare) {
         return ParseDeclare();
     }
diff --git a/lib/Parser/ParserType.cc b/lib/Parser/ParserType.cc
index 6c7703c..918b7f6 100644
--- a/lib/Parser/ParserType.cc
+++ b/lib/Parser/ParserType.cc
@@ -297,3 +297,36 @@ std::unique_ptr<StmtAST> Parser::ParseDeclare() {
         return std::make_unique<DeclareStmtAST>(Name, TypeStr);
     }
 }
+
+std::unique_ptr<StmtAST> Parser::ParseConstant() {
+    int Line = Lex.getLine();
+    getNextToken();
+    if (CurTok != tok_identifier) {
+        fprintf(stderr, "error: Expected identifier after CONSTANT at line %d\n", Line);
+        return nullptr;
+    }
+    std::string Name = Lex.IdentifierStr;
+    getNextToken();
+    if (CurTok != tok_eq) {
+        fprintf(stderr, "error: Expected '=' in CONSTANT declaration at line %d\n", Line);
+        return nullptr;
+    }
+    getNextToken();
+    bool Negative = CurTok == '-';
+    if (Negative) getNextToken();
+    bool Numeric = CurTok == tok_number_int || CurTok == tok_number_real;
+    bool Literal = Numeric || CurTok == tok_true || CurTok == tok_false ||
+                   CurTok == tok_string_literal || CurTok == tok_char_literal;
+    if (!Literal || (Negative && !Numeric)) {
+        fprintf(stderr, "error: CONSTANT initializer must be a literal at line %d\n", Line);
+        return nullptr;
+    }
+    auto Value = ParsePrimary();
+    if (!Value) return nullptr;
+    if (Negative) Value = std::make_unique<UnaryExprAST>('-', std::move(Value));
+    if (GetTokPrecedence() >= 0) {
+        fprintf(stderr, "error: CONSTANT initializer must be a literal, not an expression, at line %d\n", Line);
+        return nullptr;
+    }
+    return std::make_unique<ConstantStmtAST>(std::move(Name), std::move(Value));
+}