From 41d3bb0f3d696ce7dffc5ff1b04381d23ff8cf93 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Tue, 16 Dec 2025 19:19:46 +0300
Subject: [PATCH] Implement functions in parser & interpreter

---
 apps/interpreter/source/main.cpp              | 16 ++++
 examples/test.psl                             |  9 +-
 libs/ast/include/pslang/ast/expression.hpp    |  4 +-
 .../ast/include/pslang/ast/expression_fwd.hpp |  2 +-
 libs/ast/include/pslang/ast/function.hpp      | 33 +++++++
 libs/ast/include/pslang/ast/print.hpp         |  3 +
 libs/ast/include/pslang/ast/statement.hpp     | 10 +-
 libs/ast/include/pslang/ast/statement_fwd.hpp |  4 +-
 libs/ast/source/print.cpp                     | 38 ++++++++
 .../include/pslang/interpreter/context.hpp    | 12 +++
 .../include/pslang/interpreter/value.hpp      |  4 +
 libs/interpreter/source/eval.cpp              | 96 ++++++++++++++++++-
 libs/interpreter/source/interpreter.cpp       | 77 +++++++++++++--
 libs/interpreter/source/value.cpp             | 10 ++
 libs/parser/rules/pslang.l                    |  4 +
 libs/parser/rules/pslang.y                    | 37 +++++++
 libs/parser/source/finilize.cpp               | 11 +++
 libs/type/include/pslang/type/type_fwd.hpp    |  2 +-
 spec.txt                                      |  4 -
 19 files changed, 355 insertions(+), 21 deletions(-)
 create mode 100644 libs/ast/include/pslang/ast/function.hpp

diff --git a/apps/interpreter/source/main.cpp b/apps/interpreter/source/main.cpp
index 11286da..7d63da0 100644
--- a/apps/interpreter/source/main.cpp
+++ b/apps/interpreter/source/main.cpp
@@ -2,6 +2,7 @@
 #include <pslang/parser/error.hpp>
 #include <pslang/interpreter/interpreter.hpp>
 #include <pslang/ast/statement.hpp>
+#include <pslang/ast/print.hpp>
 
 #include <iostream>
 #include <cstring>
@@ -14,6 +15,7 @@ int main(int argc, char ** argv) try
 		std::cout << "Available options:\n";
 		std::cout << "    -t, --trace        Trace each line of execution\n";
 		std::cout << "    -d, --dump         Dump all variables after processing each file\n";
+		std::cout << "    -p, --print        Print the AST after parsing each file\n";
 		return 0;
 	}
 
@@ -22,6 +24,7 @@ int main(int argc, char ** argv) try
 	auto context = interpreter::empty_context();
 
 	bool dump = false;
+	bool dump_ast = false;
 
 	for (int arg = 1; arg < argc; ++arg)
 	{
@@ -37,7 +40,20 @@ int main(int argc, char ** argv) try
 			continue;
 		}
 
+		if (std::strcmp(argv[arg], "-p") == 0 || std::strcmp(argv[arg], "--print") == 0)
+		{
+			dump_ast = true;
+			continue;
+		}
+
 		auto ast = parser::parse(argv[arg]);
+
+		if (dump_ast)
+		{
+			ast::print(std::cout, ast);
+			std::cout << std::flush;
+		}
+
 		interpreter::execute(context, ast);
 
 		if (dump)
diff --git a/examples/test.psl b/examples/test.psl
index 9f30fa9..09b5dce 100644
--- a/examples/test.psl
+++ b/examples/test.psl
@@ -1,3 +1,6 @@
-let n = 10 + (1u as i32)
-let x = (n as f32) / 3.0
-x = 15.2
+func factorial(n : u32) -> u32:
+	if n == 0u:
+		return 1u
+	return n * factorial(n - 1u)
+
+let x = factorial(10u)
diff --git a/libs/ast/include/pslang/ast/expression.hpp b/libs/ast/include/pslang/ast/expression.hpp
index a4de813..b23db1e 100644
--- a/libs/ast/include/pslang/ast/expression.hpp
+++ b/libs/ast/include/pslang/ast/expression.hpp
@@ -4,6 +4,7 @@
 #include <pslang/ast/identifier.hpp>
 #include <pslang/ast/operation.hpp>
 #include <pslang/ast/cast.hpp>
+#include <pslang/ast/function.hpp>
 #include <pslang/ast/expression_fwd.hpp>
 
 namespace pslang::ast
@@ -27,7 +28,8 @@ namespace pslang::ast
 		identifier,
 		unary_operation,
 		binary_operation,
-		cast_operation
+		cast_operation,
+		function_call
 	>;
 
 	struct expression
diff --git a/libs/ast/include/pslang/ast/expression_fwd.hpp b/libs/ast/include/pslang/ast/expression_fwd.hpp
index af492fd..f23ef2b 100644
--- a/libs/ast/include/pslang/ast/expression_fwd.hpp
+++ b/libs/ast/include/pslang/ast/expression_fwd.hpp
@@ -7,6 +7,6 @@ namespace pslang::ast
 
 	struct expression;
 
-	using expression_ptr = std::unique_ptr<expression>;
+	using expression_ptr = std::shared_ptr<expression>;
 
 }
diff --git a/libs/ast/include/pslang/ast/function.hpp b/libs/ast/include/pslang/ast/function.hpp
new file mode 100644
index 0000000..f77a276
--- /dev/null
+++ b/libs/ast/include/pslang/ast/function.hpp
@@ -0,0 +1,33 @@
+#pragma once
+
+#include <pslang/ast/statement_fwd.hpp>
+#include <pslang/ast/expression_fwd.hpp>
+#include <pslang/type/type_fwd.hpp>
+
+#include <string>
+#include <vector>
+
+namespace pslang::ast
+{
+
+	struct function_definition
+	{
+		struct argument
+		{
+			std::string name;
+			type::type_ptr type;
+		};
+
+		std::string name;
+		std::vector<argument> arguments;
+		type::type_ptr return_type;
+		statement_list_ptr statements;
+	};
+
+	struct function_call
+	{
+		std::string name;
+		std::vector<expression_ptr> arguments;
+	};
+
+}
diff --git a/libs/ast/include/pslang/ast/print.hpp b/libs/ast/include/pslang/ast/print.hpp
index 6556fef..2cfbc8b 100644
--- a/libs/ast/include/pslang/ast/print.hpp
+++ b/libs/ast/include/pslang/ast/print.hpp
@@ -29,6 +29,7 @@ namespace pslang::ast
 	void print(std::ostream & out, unary_operation const & node, print_options const & options = {});
 	void print(std::ostream & out, binary_operation const & node, print_options const & options = {});
 	void print(std::ostream & out, cast_operation const & node, print_options const & options = {});
+	void print(std::ostream & out, function_call const & node, print_options const & options = {});
 	void print(std::ostream & out, expression_ptr const & node, print_options const & options = {});
 	void print(std::ostream & out, assignment const & node, print_options const & options = {});
 	void print(std::ostream & out, variable_declaration const & node, print_options const & options = {});
@@ -37,6 +38,8 @@ namespace pslang::ast
 	void print(std::ostream & out, else_if_block const & node, print_options const & options = {});
 	void print(std::ostream & out, if_chain const & node, print_options const & options = {});
 	void print(std::ostream & out, while_block const & node, print_options const & options = {});
+	void print(std::ostream & out, function_definition const & node, print_options const & options = {});
+	void print(std::ostream & out, return_statement const & node, print_options const & options = {});
 	void print(std::ostream & out, statement_ptr const & node, print_options const & options = {});
 	void print(std::ostream & out, statement_list_ptr const & node, print_options const & options = {});
 
diff --git a/libs/ast/include/pslang/ast/statement.hpp b/libs/ast/include/pslang/ast/statement.hpp
index ad02dbc..a5c3649 100644
--- a/libs/ast/include/pslang/ast/statement.hpp
+++ b/libs/ast/include/pslang/ast/statement.hpp
@@ -3,6 +3,7 @@
 #include <pslang/ast/expression.hpp>
 #include <pslang/ast/value_category.hpp>
 #include <pslang/ast/control.hpp>
+#include <pslang/ast/function.hpp>
 #include <pslang/ast/statement_fwd.hpp>
 #include <pslang/type/type.hpp>
 
@@ -25,6 +26,11 @@ namespace pslang::ast
 		expression_ptr rhs;
 	};
 
+	struct return_statement
+	{
+		expression_ptr value;
+	};
+
 	using statement_impl = std::variant<
 		expression_ptr,
 		assignment,
@@ -33,7 +39,9 @@ namespace pslang::ast
 		else_block,
 		else_if_block,
 		if_chain,
-		while_block
+		while_block,
+		function_definition,
+		return_statement
 	>;
 
 	struct statement
diff --git a/libs/ast/include/pslang/ast/statement_fwd.hpp b/libs/ast/include/pslang/ast/statement_fwd.hpp
index d2f4856..134aaa9 100644
--- a/libs/ast/include/pslang/ast/statement_fwd.hpp
+++ b/libs/ast/include/pslang/ast/statement_fwd.hpp
@@ -8,13 +8,13 @@ namespace pslang::ast
 
 	struct statement;
 
-	using statement_ptr = std::unique_ptr<statement>;
+	using statement_ptr = std::shared_ptr<statement>;
 
 	struct statement_list
 	{
 		std::vector<statement_ptr> statements;
 	};
 
-	using statement_list_ptr = std::unique_ptr<statement_list>;
+	using statement_list_ptr = std::shared_ptr<statement_list>;
 
 }
diff --git a/libs/ast/source/print.cpp b/libs/ast/source/print.cpp
index 392f878..3e50c46 100644
--- a/libs/ast/source/print.cpp
+++ b/libs/ast/source/print.cpp
@@ -143,6 +143,15 @@ namespace pslang::ast
 		print(out, node.expression, child(options));
 	}
 
+	void print(std::ostream & out, function_call const & node, print_options const & options)
+	{
+		put_indent(out, options);
+		out << "call " << node.name;
+		newline(out);
+		for (auto const & argument : node.arguments)
+			print(out, argument, child(options));
+	}
+
 	void print(std::ostream & out, expression_ptr const & node, print_options const & options)
 	{
 		std::visit([&](auto const & value){ print(out, value, options); }, *node);
@@ -232,6 +241,35 @@ namespace pslang::ast
 		print(out, node.statements, child(options));
 	}
 
+	void print(std::ostream & out, function_definition const & node, print_options const & options)
+	{
+		put_indent(out, options);
+		out << "function { name = \"" << node.name << "\", return type = ";
+		type::print(out, *node.return_type);
+		out << " }";
+		newline(out);
+		for (auto const & arg : node.arguments)
+		{
+			put_indent(out, child(options));
+			out << "argument { name = \"" << arg.name << "\", type = ";
+			type::print(out, *arg.type);
+			out << " }";
+			newline(out);
+		}
+		put_indent(out, child(options));
+		out << "body";
+		newline(out);
+		print(out, node.statements, child(child(options)));
+	}
+
+	void print(std::ostream & out, return_statement const & node, print_options const & options)
+	{
+		put_indent(out, options);
+		out << "return";
+		newline(out);
+		print(out, node.value, child(options));
+	}
+
 	void print(std::ostream & out, statement_ptr const & node, print_options const & options)
 	{
 		std::visit([&](auto const & value){ print(out, value, options); }, *node);
diff --git a/libs/interpreter/include/pslang/interpreter/context.hpp b/libs/interpreter/include/pslang/interpreter/context.hpp
index bdb6a20..9a554d2 100644
--- a/libs/interpreter/include/pslang/interpreter/context.hpp
+++ b/libs/interpreter/include/pslang/interpreter/context.hpp
@@ -2,6 +2,7 @@
 
 #include <pslang/interpreter/value.hpp>
 #include <pslang/ast/value_category.hpp>
+#include <pslang/ast/function.hpp>
 
 #include <unordered_map>
 #include <string>
@@ -17,9 +18,20 @@ namespace pslang::interpreter
 		interpreter::value value;
 	};
 
+	struct function_data
+	{
+		std::vector<ast::function_definition::argument> arguments;
+		type::type_ptr return_type;
+		ast::statement_list_ptr statements;
+	};
+
 	struct scope
 	{
 		std::unordered_map<std::string, variable_data> variables;
+		std::unordered_map<std::string, function_data> functions;
+
+		bool is_function_scope = false;
+		value return_value = unit_value{};
 	};
 
 	struct context
diff --git a/libs/interpreter/include/pslang/interpreter/value.hpp b/libs/interpreter/include/pslang/interpreter/value.hpp
index 3369672..a980aa5 100644
--- a/libs/interpreter/include/pslang/interpreter/value.hpp
+++ b/libs/interpreter/include/pslang/interpreter/value.hpp
@@ -9,6 +9,9 @@
 namespace pslang::interpreter
 {
 
+	struct unit_value
+	{};
+
 	template <typename T>
 	struct primitive_value_base
 	{
@@ -51,6 +54,7 @@ namespace pslang::interpreter
 	};
 
 	using value_impl = std::variant<
+		unit_value,
 		primitive_value
 	>;
 
diff --git a/libs/interpreter/source/eval.cpp b/libs/interpreter/source/eval.cpp
index 8079cc4..25d6a43 100644
--- a/libs/interpreter/source/eval.cpp
+++ b/libs/interpreter/source/eval.cpp
@@ -83,7 +83,7 @@ namespace pslang::interpreter
 		template <typename T>
 		value eval_impl(context & context, ast::numeric_literal_base<T> const & literal)
 		{
-			return primitive_value(primitive_value_base<T>{literal.value});;
+			return primitive_value(primitive_value_base<T>{literal.value});
 		}
 
 		value eval_impl(context & context, ast::literal const & literal)
@@ -102,6 +102,15 @@ namespace pslang::interpreter
 			throw std::runtime_error("Identifier \"" + identifier.name + "\" is not defined");
 		}
 
+		value unary_operation_impl(ast::unary_operation_type type, unit_value const &)
+		{
+			std::ostringstream os;
+			os << "Cannot apply unary operator \"";
+			print(os, type);
+			os << "\" to a value of type unit";
+			throw std::runtime_error(os.str());
+		}
+
 		template <typename T>
 		value unary_operation_impl(ast::unary_operation_type type, primitive_value_base<T> const & arg1)
 		{
@@ -251,6 +260,16 @@ namespace pslang::interpreter
 			throw std::runtime_error(os.str());
 		}
 
+		value binary_operation_impl_same_type(ast::binary_operation_type type, unit_value const &, value const & arg2)
+		{
+			std::ostringstream os;
+			os << "Cannot apply binary operator \"";
+			print(os, type);
+			os << "\" to values of type unit and ";
+			type::print(os, type_of(arg2));
+			throw std::runtime_error(os.str());
+		}
+
 		value binary_operation_impl_same_type(ast::binary_operation_type type, primitive_value const & arg1, value const & arg2)
 		{
 			return std::visit([&](auto const & value){ return binary_operation_impl_same_type(type, value, arg2); }, arg1);
@@ -284,6 +303,20 @@ namespace pslang::interpreter
 			throw std::runtime_error("eval(binary_operation) for different argument types not implemented");
 		}
 
+		value cast_impl(unit_value const & value, type::type const & type)
+		{
+			if (type::equal(type, type::unit_type{}))
+				return value;
+
+			throw std::runtime_error("Cannot cast unit type to anything");
+		}
+
+		template <typename T>
+		value cast_impl(primitive_value_base<T> const & value, type::unit_type const &)
+		{
+			throw std::runtime_error("Cannot cast anything to unit type");
+		}
+
 		template <typename T, typename H>
 		value cast_impl(primitive_value_base<T> const & value, type::primitive_type_base<H> const & type)
 		{
@@ -327,6 +360,67 @@ namespace pslang::interpreter
 			return std::visit([&](auto const & value){ return cast_impl(value, *cast_operation.type); }, arg);
 		}
 
+		value eval_impl(context & context, ast::function_call const & function_call)
+		{
+			for (auto it = context.scope_stack.rbegin(); it != context.scope_stack.rend(); ++it)
+			{
+				if (auto jt = it->functions.find(function_call.name); jt != it->functions.end())
+				{
+					if (jt->second.arguments.size() != function_call.arguments.size())
+					{
+						std::ostringstream os;
+						os << "Cannot call function \"" << function_call.name << "\": expected " << jt->second.arguments.size() << " arguments, got " << function_call.arguments.size();
+						throw std::runtime_error(os.str());
+					}
+
+					std::vector<value> args;
+					for (auto const & expression : function_call.arguments)
+						args.push_back(eval(context, expression));
+
+					for (std::size_t i = 0; i < args.size(); ++i)
+					{
+						auto actual_type = type_of(args[i]);
+						if (!type::equal(actual_type, *jt->second.arguments[i].type))
+						{
+							std::ostringstream os;
+							os << "Cannot call function \"" << function_call.name << "\": argument #" << (i + 1) << " expects type ";
+							type::print(os, *jt->second.arguments[i].type);
+							os << " but actual type is ";
+							type::print(os, actual_type);
+							throw std::runtime_error(os.str());
+						}
+					}
+
+					auto & function_scope = context.scope_stack.emplace_back();
+					function_scope.is_function_scope = true;
+
+					for (std::size_t i = 0; i < args.size(); ++i)
+						function_scope.variables[jt->second.arguments[i].name] = {.category = ast::value_category::constant, .value = std::move(args[i])};
+
+					auto expected_return_type = jt->second.return_type;
+
+					execute(context, jt->second.statements);
+
+					auto actual_return_type = type_of(context.scope_stack.back().return_value);
+					if (!type::equal(actual_return_type, *expected_return_type))
+					{
+						std::ostringstream os;
+						os << "Error returning from function \"" << function_call.name << "\": expected return type is ";
+						type::print(os, *expected_return_type);
+						os << " but actual type is ";
+						type::print(os, actual_return_type);
+						throw std::runtime_error(os.str());
+					}
+
+					auto result = std::move(context.scope_stack.back().return_value);
+					context.scope_stack.pop_back();
+					return result;
+				}
+			}
+
+			throw std::runtime_error("Function \"" + function_call.name + "\" is not defined");
+		}
+
 		value eval_impl(context & context, ast::expression_ptr const & expression)
 		{
 			return std::visit([&](auto const & expression){ return eval_impl(context, expression); }, *expression);
diff --git a/libs/interpreter/source/interpreter.cpp b/libs/interpreter/source/interpreter.cpp
index 6579a96..19b7f13 100644
--- a/libs/interpreter/source/interpreter.cpp
+++ b/libs/interpreter/source/interpreter.cpp
@@ -12,6 +12,24 @@ namespace pslang::interpreter
 	namespace
 	{
 
+		struct return_exception
+		{};
+
+		struct stack_pop_guard
+		{
+			stack_pop_guard(context & context)
+				: context_(context)
+			{}
+
+			~stack_pop_guard()
+			{
+				context_.scope_stack.pop_back();
+			}
+
+		private:
+			context & context_;
+		};
+
 		void execute_impl(context & context, ast::expression_ptr const & expression)
 		{
 			eval(context, expression);
@@ -72,7 +90,7 @@ namespace pslang::interpreter
 					throw std::runtime_error(os.str());
 				}
 			}
-			scope.variables[variable_declaration.name] = {.category = variable_declaration.category, .value = value};
+			context.scope_stack.back().variables[variable_declaration.name] = {.category = variable_declaration.category, .value = value};
 		}
 
 		void execute_impl(context & context, ast::if_block const &)
@@ -94,6 +112,8 @@ namespace pslang::interpreter
 		{
 			for (auto const & block : if_chain.blocks)
 			{
+				bool do_execute = true;
+
 				if (block.condition)
 				{
 					auto value = eval(context, block.condition);
@@ -107,12 +127,16 @@ namespace pslang::interpreter
 						throw std::runtime_error(os.str());
 					}
 
-					if (std::get<bool_value>(std::get<primitive_value>(value)).value)
-					{
-						execute(context, block.statements);
-						break;
-					}
+					do_execute = std::get<bool_value>(std::get<primitive_value>(value)).value;
 				}
+
+				if (!do_execute)
+					continue;
+
+				context.scope_stack.emplace_back();
+				stack_pop_guard guard(context);
+				execute(context, block.statements);
+				break;
 			}
 		}
 
@@ -133,6 +157,8 @@ namespace pslang::interpreter
 
 				if (std::get<bool_value>(std::get<primitive_value>(value)).value)
 				{
+					context.scope_stack.emplace_back();
+					stack_pop_guard guard(context);
 					execute(context, while_block.statements);
 				}
 				else
@@ -140,11 +166,48 @@ namespace pslang::interpreter
 			}
 		}
 
+		void execute_impl(context & context, ast::function_definition const & function_definition)
+		{
+			auto & scope = context.scope_stack.back();
+			if (scope.functions.count(function_definition.name) > 0)
+				throw std::runtime_error("Function \"" + function_definition.name + "\" is already defined");
+
+			auto & function = scope.functions[function_definition.name];
+			function.arguments = function_definition.arguments;
+			function.return_type = function_definition.return_type;
+			function.statements = function_definition.statements;
+		}
+
+		void execute_impl(context & context, ast::return_statement const & return_statement)
+		{
+			auto value = eval(context, return_statement.value);
+			for (auto it = context.scope_stack.rbegin(); it != context.scope_stack.rend(); ++it)
+			{
+				if (it->is_function_scope)
+				{
+					it->return_value = std::move(value);
+					throw return_exception{};
+				}
+			}
+
+			throw std::runtime_error("Cannot return outside of a function");
+		}
+
 		void execute_impl(context & context, ast::statement_list_ptr const & statements)
 		{
 			for (auto const & statement : statements->statements)
 			{
-				std::visit([&](auto const & statement){ execute_impl(context, statement); }, *statement);
+				try
+				{
+					std::visit([&](auto const & statement){ execute_impl(context, statement); }, *statement);
+				}
+				catch (return_exception const &)
+				{
+					if (context.scope_stack.back().is_function_scope)
+						break;
+					else
+						throw;
+				}
 			}
 		}
 
diff --git a/libs/interpreter/source/value.cpp b/libs/interpreter/source/value.cpp
index c89570e..dad9e92 100644
--- a/libs/interpreter/source/value.cpp
+++ b/libs/interpreter/source/value.cpp
@@ -8,6 +8,11 @@ namespace pslang::interpreter
 	namespace
 	{
 
+		type::type type_of_impl(unit_value const &)
+		{
+			return type::unit_type{};
+		}
+
 		template <typename T>
 		type::type type_of_impl(primitive_value_base<T> const &)
 		{
@@ -24,6 +29,11 @@ namespace pslang::interpreter
 			return std::visit([](auto const & value){ return type_of_impl(value); }, value);
 		}
 
+		void print_impl(std::ostream & out, unit_value const &)
+		{
+			out << "unit";
+		}
+
 		template <typename T>
 		void print_impl(std::ostream & out, primitive_value_base<T> const & value)
 		{
diff --git a/libs/parser/rules/pslang.l b/libs/parser/rules/pslang.l
index 0a19f0b..8d0206b 100644
--- a/libs/parser/rules/pslang.l
+++ b/libs/parser/rules/pslang.l
@@ -28,6 +28,8 @@ if    { return bp::make_if(ctx.location); }
 else  { return bp::make_else(ctx.location); }
 while { return bp::make_while(ctx.location); }
 as    { return bp::make_as(ctx.location); }
+func  { return bp::make_func(ctx.location); }
+return { return bp::make_return(ctx.location); }
 true  { return bp::make_true(ctx.location); }
 false { return bp::make_false(ctx.location); }
 
@@ -50,6 +52,7 @@ f64  { return bp::make_f64(ctx.location); }
 "\t" { return bp::make_indent(ctx.location); }
 "="  { return bp::make_assignment(ctx.location); }
 ":"  { return bp::make_colon(ctx.location); }
+","  { return bp::make_comma(ctx.location); }
 "("  { return bp::make_lparen(ctx.location); }
 ")"  { return bp::make_rparen(ctx.location); }
 "+"  { return bp::make_plus(ctx.location); }
@@ -67,6 +70,7 @@ f64  { return bp::make_f64(ctx.location); }
 ">"  { return bp::make_greater(ctx.location); }
 "<=" { return bp::make_less_equals(ctx.location); }
 ">=" { return bp::make_greater_equals(ctx.location); }
+"->" { return bp::make_arrow(ctx.location); }
 
 [0-9]+b  { return bp::make_lit_i8(yytext, ctx.location); }
 [0-9]+ub { return bp::make_lit_u8(yytext, ctx.location); }
diff --git a/libs/parser/rules/pslang.y b/libs/parser/rules/pslang.y
index 9874d9e..f1514d5 100644
--- a/libs/parser/rules/pslang.y
+++ b/libs/parser/rules/pslang.y
@@ -75,6 +75,7 @@ template <typename T>
 %token indent "indentation"
 %token assignment "="
 %token colon ":"
+%token comma ","
 %token lparen "("
 %token rparen ")"
 %token plus "+"
@@ -92,6 +93,7 @@ template <typename T>
 %token greater ">"
 %token less_equals "<="
 %token greater_equals ">="
+%token arrow "->"
 
 %token <std::string> lit_i8
 %token <std::string> lit_u8
@@ -116,6 +118,8 @@ template <typename T>
 %token else
 %token while
 %token as
+%token func
+%token return
 %token true
 %token false
 
@@ -137,6 +141,9 @@ template <typename T>
 %type <indented_statement_list> indented_statement_list
 %type <std::size_t> indentation
 %type <ast::statement> statement
+%type <std::vector<ast::function_definition::argument>> function_definition_argument_list
+%type <std::vector<ast::function_definition::argument>> nonempty_function_definition_argument_list
+%type <type::type_ptr> function_return_type
 %type <ast::variable_declaration> variable_declaration
 %type <ast::value_category> variable_keyword
 %type <type::type> type_expression
@@ -150,6 +157,8 @@ template <typename T>
 %type <ast::expression> mult_expression
 %type <ast::expression> not_expression
 %type <ast::expression> base_expression
+%type <std::vector<ast::expression_ptr>> function_call_argument_list
+%type <std::vector<ast::expression_ptr>> nonempty_function_call_argument_list
 %type <ast::expression> literal
 
 %%
@@ -177,6 +186,23 @@ statement
 | else colon { $$ = ast::else_block{{}}; }
 | else if expression colon { $$ = ast::else_if_block{std::make_unique<ast::expression>($3), {}}; }
 | while expression colon { $$ = ast::while_block{std::make_unique<ast::expression>($2), {}}; }
+| func name lparen function_definition_argument_list rparen function_return_type colon { $$ = ast::function_definition{$2, $4, $6, {}}; }
+| return expression { $$ = ast::return_statement{std::make_unique<ast::expression>($2)}; }
+;
+
+function_definition_argument_list
+: %empty { std::vector<ast::function_definition::argument> tmp; $$ = std::move(tmp); }
+| nonempty_function_definition_argument_list { $$ = $1; }
+;
+
+nonempty_function_definition_argument_list
+: name colon type_expression { std::vector<ast::function_definition::argument> tmp; tmp.push_back({.name = $1, .type = std::make_unique<type::type>($3)}); $$ = std::move(tmp); }
+| nonempty_function_definition_argument_list comma name colon type_expression { auto tmp = $1; tmp.push_back({.name = $3, .type = std::make_unique<type::type>($5)}); $$ = std::move(tmp); }
+;
+
+function_return_type
+: arrow type_expression { $$ = std::make_unique<type::type>($2); }
+| %empty { $$ = std::make_unique<type::type>(type::unit_type{}); }
 ;
 
 variable_declaration
@@ -262,6 +288,17 @@ base_expression
 : literal
 | name { $$ = ast::identifier{$1}; }
 | lparen expression rparen { $$ = $2; }
+| name lparen function_call_argument_list rparen { $$ = ast::function_call{$1, $3}; }
+;
+
+function_call_argument_list
+: %empty { std::vector<ast::expression_ptr> tmp; $$ = std::move(tmp); }
+| nonempty_function_call_argument_list
+;
+
+nonempty_function_call_argument_list
+: expression { std::vector<ast::expression_ptr> tmp; tmp.push_back(std::make_unique<ast::expression>($1)); $$ = std::move(tmp); }
+| nonempty_function_call_argument_list comma expression { auto tmp = $1; tmp.push_back(std::make_unique<ast::expression>($3)); $$ = std::move(tmp); }
 ;
 
 literal
diff --git a/libs/parser/source/finilize.cpp b/libs/parser/source/finilize.cpp
index 895f61f..da5f755 100644
--- a/libs/parser/source/finilize.cpp
+++ b/libs/parser/source/finilize.cpp
@@ -55,6 +55,17 @@ namespace pslang::parser
 			return node.statements.get();
 		}
 
+		ast::statement_list * get_statement_list(ast::function_definition & node)
+		{
+			node.statements = std::make_unique<ast::statement_list>();
+			return node.statements.get();
+		}
+
+		ast::statement_list * get_statement_list(ast::return_statement &)
+		{
+			return nullptr;
+		}
+
 		ast::statement_list * get_statement_list(ast::statement & statement)
 		{
 			return std::visit([](auto & value){ return get_statement_list(value); }, statement);
diff --git a/libs/type/include/pslang/type/type_fwd.hpp b/libs/type/include/pslang/type/type_fwd.hpp
index 26c647e..07b7084 100644
--- a/libs/type/include/pslang/type/type_fwd.hpp
+++ b/libs/type/include/pslang/type/type_fwd.hpp
@@ -7,6 +7,6 @@ namespace pslang::type
 
 	struct type;
 
-	using type_ptr = std::unique_ptr<type>;
+	using type_ptr = std::shared_ptr<type>;
 
 }
diff --git a/spec.txt b/spec.txt
index a3963a2..2e42b97 100644
--- a/spec.txt
+++ b/spec.txt
@@ -146,10 +146,6 @@ Function types:
     (T1, T2, T3) -> i32
     (T1, T2) -> unit // no return value
 
-Function declaration (required for e.g. loops in call graph):
-    func foo(x: i32, y: i32) -> i32
-    func bar(x: f32) // same as -> unit
-
 Function definition:
     func foo(x: i32, y: i32) -> i32:
         return x * y