diff --git a/libjlx/modules/ast.cppm b/libjlx/modules/ast.cppm
index 83b579c..0d698f0 100644
--- a/libjlx/modules/ast.cppm
+++ b/libjlx/modules/ast.cppm
@@ -466,6 +466,12 @@ namespace jlx {
 							next(false);
 
 							return previous;
+						} else {
+							if (previous != nullptr) {
+								return previous;
+							}
+
+							fail_invalid_token(*current);
 						}
 					}
 					fail_invalid_token(*current);
@@ -508,7 +514,7 @@ namespace jlx {
 			std::optional<std::string> return_type;
 
 			bool first = true;
-			while (current->type != Punctuation && current->content != ")") {
+			while (current->type != Punctuation || current->content != ")") {
 				if (!first) {
 					if(current->type != Punctuation || current->content != ",") {
 						fail_invalid_token(*current);
@@ -534,8 +540,8 @@ namespace jlx {
 
 				auto param_type = parse_type();
 				params.emplace_back(std::move(name), std::move(param_type));
-
 				next();
+
 				first = false;
 			}
 			next();
diff --git a/libjlx/modules/tokenizer.cppm b/libjlx/modules/tokenizer.cppm
index 93fff78..d04b2c2 100644
--- a/libjlx/modules/tokenizer.cppm
+++ b/libjlx/modules/tokenizer.cppm
@@ -64,17 +64,11 @@ namespace jlx {
 		return std::format("{}({})", token_type_to_string(t.type), t.content);
 	}
 
-	export class tokenizer_exception {
-	protected:
-		std::string msg;
+	export class tokenizer_exception : public std::runtime_error {
 	public:
-		tokenizer_exception(std::string msg, std::size_t line, std::size_t col) : msg(std::format("Tokenizer exception at %d:%d. %s", line, col, msg)) {
+		tokenizer_exception(std::string msg, std::size_t line, std::size_t col) : std::runtime_error(std::format("Tokenizer exception at {}:{}. {}", line, col, msg).c_str()) {
 
 		}
-
-		const std::string& what() const {
-			return msg;
-		}
 	};
 
 	export class tokenizer {
@@ -90,14 +84,15 @@ namespace jlx {
 			"return"
 		}};
 
-		static constexpr std::array<char, 7> punctuations = {{
+		static constexpr std::array<char, 8> punctuations = {{
 			'.',
 			'(',
-			'(',
+			')',
 			'{',
 			'}',
 			':',
-			';'
+			';',
+			','
 		}};
 
 		static constexpr std::array<std::string, 13> operators = {{
@@ -329,7 +324,8 @@ namespace jlx {
 				};
 			}
 
-			throw tokenizer_exception(std::format("Unknown operator '%s'", word), line, col);
+			//throw tokenizer_exception(std::format("Unknown operator '{}'", word), line, col);
+			return std::nullopt;
 		}
 
 	public:
@@ -372,7 +368,7 @@ namespace jlx {
 				return op_res;
 			}
 
-			throw tokenizer_exception(std::format("Unknown character '%c'", val), source.current_line(), source.current_col());
+			throw tokenizer_exception(std::format("Unknown character '{}'", val), source.current_line(), source.current_col());
 		}
 	};
 }
diff --git a/libjlx/modules/type_checker.cppm b/libjlx/modules/type_checker.cppm
index 09bd756..18d2303 100644
--- a/libjlx/modules/type_checker.cppm
+++ b/libjlx/modules/type_checker.cppm
@@ -478,6 +478,9 @@ namespace jlx {
 						scopes[scopes.size() - 1].functions.insert_or_assign(decl->name, f);
 
 						auto& function_scope = scopes.emplace_back(type_checker_scope{});
+						for (auto& a : decl->parameters) {
+							function_scope.variables.insert_or_assign(a.name, a.type);
+						}
 						function_scope.intended_return_type = decl->return_type;
 
 						check_statement(*decl->body, true);