From b85f552ae29ffcd136690b66450271f90c97cd6c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafa=C5=82=20Grodzi=C5=84ski?= <rafal.grodzinski@gmail.com>
Date: Thu, 19 Jun 2025 17:23:27 +0900
Subject: [PATCH] Parse extern function

---
 src/Lexer.cpp     |  5 +++++
 src/Lexer.h       |  1 -
 src/Parser.cpp    | 56 ++++++++++++++++++++++++++++++++++++++++++++++-
 src/Parser.h      |  3 +++
 src/Statement.cpp | 29 ++++++++++++++++++++++++
 src/Statement.h   | 16 ++++++++++++++
 src/Token.cpp     |  3 +++
 src/Types.h       |  3 +++
 8 files changed, 114 insertions(+), 2 deletions(-)

diff --git a/src/Lexer.cpp b/src/Lexer.cpp
index 787f5d3..c54cda7 100644
--- a/src/Lexer.cpp
+++ b/src/Lexer.cpp
@@ -230,6 +230,11 @@ shared_ptr<Token> Lexer::nextToken() {
     if (token != nullptr)
         return token;
 
+    // meta
+    token = match(TokenKind::M_EXTERN, "@extern", true);
+    if (token != nullptr)
+        return token;
+
     // new line
     token = match(TokenKind::NEW_LINE, "\n", false);
     if (token != nullptr)
diff --git a/src/Lexer.h b/src/Lexer.h
index 08bfa2d..0d756a8 100644
--- a/src/Lexer.h
+++ b/src/Lexer.h
@@ -20,7 +20,6 @@ private:
     shared_ptr<Token> match(TokenKind kind, string lexme, bool needsSeparator);
     shared_ptr<Token> matchInteger();
     shared_ptr<Token> matchReal();
-    //shared_ptr<Token> matchType();
     shared_ptr<Token> matchIdentifier();
     shared_ptr<Token> matchEnd();
     shared_ptr<Token> matchInvalid();
diff --git a/src/Parser.cpp b/src/Parser.cpp
index 30fc57b..31bed5a 100644
--- a/src/Parser.cpp
+++ b/src/Parser.cpp
@@ -41,7 +41,11 @@ shared_ptr<Statement> Parser::nextStatement() {
     if (statement != nullptr)
         return statement;
 
-    return matchStatementInvalid();
+    statement = matchStatementMetaExternFunction();
+    if (statement != nullptr)
+        return statement;
+
+    return matchStatementInvalid("Unexpected token");
 }
 
 shared_ptr<Statement> Parser::matchStatementFunctionDeclaration() {
@@ -188,6 +192,56 @@ shared_ptr<Statement> Parser::matchStatementExpression() {
     return make_shared<StatementExpression>(expression);
 }
 
+shared_ptr<Statement> Parser::matchStatementMetaExternFunction() {
+    if (!tryMatchingTokenKinds({TokenKind::M_EXTERN, TokenKind::IDENTIFIER, TokenKind::FUNCTION}, true, false))
+        return nullptr;
+
+    currentIndex++; // skip meta
+    shared_ptr<Token> identifierToken = tokens.at(currentIndex);
+    currentIndex++;
+    currentIndex++; // skip fun
+
+    // Get arguments
+    vector<pair<string, ValueType>> arguments;
+    if (tryMatchingTokenKinds({TokenKind::COLON}, true, true)) {
+        do {
+            tryMatchingTokenKinds({TokenKind::NEW_LINE}, true, true); // skip new line
+            if (!tryMatchingTokenKinds({TokenKind::IDENTIFIER, TokenKind::TYPE}, true, false))
+                return matchStatementInvalid("Expected function argument");
+            shared_ptr<Token> identifierToken = tokens.at(currentIndex);
+            currentIndex++; // identifier
+            shared_ptr<Token> typeToken = tokens.at(currentIndex);
+            currentIndex++; // type
+            optional<ValueType> argumentType = valueTypeForToken(typeToken);
+            if (!argumentType)
+                return matchStatementInvalid("Invalid argument type");
+            
+            arguments.push_back(pair<string, ValueType>(identifierToken->getLexme(), *argumentType));
+        } while (tryMatchingTokenKinds({TokenKind::COMMA}, true, true));
+    }
+
+    // consume optional new line
+    tryMatchingTokenKinds({TokenKind::NEW_LINE}, true, true);
+
+    // Return type
+    ValueType returnType = ValueType::NONE;
+    if (tryMatchingTokenKinds({TokenKind::RIGHT_ARROW}, true, true)) {
+        shared_ptr<Token> typeToken = tokens.at(currentIndex);
+        optional<ValueType> type = valueTypeForToken(typeToken);
+        if (!type)
+            return matchStatementInvalid("Expected return type");
+        returnType = *type;
+
+        currentIndex++; // type
+
+        // consume new line
+        if (!tryMatchingTokenKinds({TokenKind::NEW_LINE}, true, true))
+            return matchStatementInvalid("Expected new line after function declaration");
+    }
+
+    return make_shared<StatementMetaExternFunction>(identifierToken->getLexme(), arguments, returnType);
+}
+
 shared_ptr<StatementInvalid> Parser::matchStatementInvalid(string message) {
     return make_shared<StatementInvalid>(tokens.at(currentIndex), message);
 }
diff --git a/src/Parser.h b/src/Parser.h
index ee5eb38..d3bd810 100644
--- a/src/Parser.h
+++ b/src/Parser.h
@@ -20,6 +20,9 @@ private:
     shared_ptr<Statement> matchStatementBlock(vector<TokenKind> terminalTokenKinds, bool shouldConsumeTerminal);
     shared_ptr<Statement> matchStatementReturn();
     shared_ptr<Statement> matchStatementExpression();
+
+    shared_ptr<Statement> matchStatementMetaExternFunction();
+
     shared_ptr<StatementInvalid> matchStatementInvalid(string message = "");
 
     shared_ptr<Expression> nextExpression();
diff --git a/src/Statement.cpp b/src/Statement.cpp
index e409e17..177a7ef 100644
--- a/src/Statement.cpp
+++ b/src/Statement.cpp
@@ -176,6 +176,35 @@ string StatementExpression::toString(int indent) {
     return value;
 }
 
+//
+// Statement @ Function
+StatementMetaExternFunction::StatementMetaExternFunction(string name, vector<pair<string, ValueType>> arguments, ValueType returnValueType):
+Statement(StatementKind::META_EXTERN_FUNCTION), name(name), arguments(arguments), returnValueType(returnValueType) {
+}
+
+string StatementMetaExternFunction::getName() {
+    return name;
+}
+
+vector<pair<string, ValueType>> StatementMetaExternFunction::getArguments() {
+    return arguments;
+}
+
+ValueType StatementMetaExternFunction::getReturnValueType() {
+    return returnValueType;
+}
+
+string StatementMetaExternFunction::toString(int indent) {
+    string value;
+    for (int ind=0; ind<indent; ind++)
+        value += "  ";
+    value += "EXTERN_FUN(";
+    value += name + ", ";
+    value += valueTypeToString(returnValueType);
+    value += ")\n";
+    return value;
+}
+
 //
 // StatementInvalid
 StatementInvalid::StatementInvalid(shared_ptr<Token> token, string message):
diff --git a/src/Statement.h b/src/Statement.h
index 2e23bd8..249486d 100644
--- a/src/Statement.h
+++ b/src/Statement.h
@@ -101,6 +101,22 @@ public:
     string toString(int indent) override;
 };
 
+//
+// Statement @ Extern Function
+class StatementMetaExternFunction: public Statement {
+private:
+    string name;
+    vector<pair<string, ValueType>> arguments;
+    ValueType returnValueType;
+
+public:
+    StatementMetaExternFunction(string name, vector<pair<string, ValueType>> arguments, ValueType returnValueType);
+    string getName();
+    vector<pair<string, ValueType>> getArguments();
+    ValueType getReturnValueType();
+    string toString(int indent) override;
+};
+
 //
 // StatementInvalid
 class StatementInvalid: public Statement {
diff --git a/src/Token.cpp b/src/Token.cpp
index fb1e6a7..5c6700b 100644
--- a/src/Token.cpp
+++ b/src/Token.cpp
@@ -135,6 +135,9 @@ string Token::toString() {
         case TokenKind::RETURN:
             return "RETURN";
 
+        case TokenKind::M_EXTERN:
+            return "@EXTERN";
+
         case TokenKind::NEW_LINE:
             return "↲";
         case TokenKind::END:
diff --git a/src/Types.h b/src/Types.h
index 547efdf..6291e2f 100644
--- a/src/Types.h
+++ b/src/Types.h
@@ -34,6 +34,8 @@ enum class TokenKind {
     IDENTIFIER,
     TYPE,
 
+    M_EXTERN,
+
     NEW_LINE,
     END,
 
@@ -56,6 +58,7 @@ enum class StatementKind {
     BLOCK,
     RETURN,
     EXPRESSION,
+    META_EXTERN_FUNCTION,
     INVALID
 };