UserScript/src/parse.cpp

#include <optional>
#include <algorithm>
#include "UserScript/parser.h"
#include "UserScript.h"

//////////////////////
/// PARSER HELPERS ///
//////////////////////

using token = scripting::ast::token;
using symbol_t = scripting::ast::symbol_t;

template<typename T>
struct parse_result {
	std::optional<T> result;
	std::span<token> rest;
	operator bool() { return result.has_value(); }
};

bool next_is_newline(std::span<token> current) {
	return (not current.empty()) && (holds_alternative<symbol_t>(current.front().value) && (get<symbol_t>(current.front().value) == symbol_t::new_line));
}

std::span<token> trim_newline(std::span<token> current) {
	while(next_is_newline(current)) {
		current = current.subspan(1);
	}
	return current;
}

///////////////////////////
/// PARSER DECLARATIONS ///
///////////////////////////

parse_result<scripting::ast::expression> try_expression(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::binary_algebraic_expression> try_binary_algebraic_expression(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::variable_expression> try_variable_expression(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::literal_int_expression> try_literal_int_expression(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::literal_string_expression> try_literal_string_expression(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::statement> try_statement(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::command_expression> try_command_expr(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::conditional> try_conditional(const std::span<token> code, std::vector<scripting::script_error>& errors, const std::string_view initiator = "if");
parse_result<scripting::ast::while_loop> try_while_loop(const std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::paren_expression> try_paren_expression(std::span<token> code, std::vector<scripting::script_error>& errors);
parse_result<scripting::ast::unary_algebraic_expression> try_unary_algebraic_expression(std::span<token> code, std::vector<scripting::script_error>& errors);


//////////////////////////
/// PARSER DEFINITIONS ///
//////////////////////////

parse_result<scripting::ast::command_expression> try_command_expr(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::command_expression cmd;
	auto current = code;
	if(current.empty()) return {std::nullopt, code};
	if(not holds_alternative<symbol_t>(current.front().value)) return {std::nullopt, code};
	if(get<symbol_t>(current.front().value) != symbol_t::divide) return {std::nullopt, code};
	cmd.location = current.front().location;
	current = current.subspan(1);
	
	if(current.empty()) {
		errors.push_back(
			scripting::script_error{.location = code.front().location, .message = "Expected command name"});
		return {std::nullopt, code};
	}
	if(not holds_alternative<scripting::ast::identifier>(current.front().value))  {
		errors.push_back(
			scripting::script_error{.location = current.front().location, .message = "Expected command name"});
		return {std::nullopt, code};
	}
	cmd.name = get<scripting::ast::identifier>(current.front().value);
	current = current.subspan(1);
	
	while(
		not current.empty()
		and not (
			holds_alternative<symbol_t>(current.front().value)
			and get<symbol_t>(current.front().value) == symbol_t::new_line
		)
		and not (
			holds_alternative<symbol_t>(current.front().value)
			and get<symbol_t>(current.front().value) == symbol_t::r_paren
		)
		) {
		auto [expr, rest] = try_expression(current, errors);
		
		if(not expr) {
			errors.push_back(
				scripting::script_error{.location = current.front().location, .message = "Expected expression"});
			return {std::nullopt, code};
		}
		
		cmd.arguments.push_back(std::make_unique<scripting::ast::expression>(std::move(expr.value())));
		current = rest;
	}
	
	return {std::move(cmd), current};
}

parse_result<scripting::ast::expression> try_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::expression node;
	auto current = code;

#ifdef HANDLE_EXPRESSION
	static_assert(false, "Found a macro name HANDLE_EXPRESSION, halting");
#endif
#define HANDLE_EXPRESSION(type) \
	node = scripting::ast::expression{ \
		.location = current.front().location, \
		.contents = std::make_unique<type>(std::move(expr.value())) \
	}; \
	current = rest;
	
	if(auto [expr, rest] = try_binary_algebraic_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::binary_algebraic_expression)
	} else if(auto [expr, rest] = try_literal_string_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::literal_string_expression)
	} else if(auto [expr, rest] = try_literal_int_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::literal_int_expression)
	} else if(auto [expr, rest] = try_unary_algebraic_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::unary_algebraic_expression)
	} else if(auto [expr, rest] = try_paren_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::paren_expression)
	} else if(auto [expr, rest] = try_variable_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::variable_expression)
	} else {
		return {std::nullopt, code};
	}
#undef HANDLE_EXPRESSION
	return {.result = std::move(node), .rest = current};
}

parse_result<scripting::ast::conditional> try_conditional(const std::span<token> code, std::vector<scripting::script_error>& errors, const std::string_view initiator) {
#ifdef FAILURE
	static_assert(false, "Found a macro name FAILURE, halting");
#endif
#define FAILURE {.result = std::nullopt, .rest = code}
	scripting::ast::conditional result{};
	if(code.empty()) return FAILURE;
	auto current = code;
	result.location = current.front().location;
	
	const auto endif_found = [&]() -> bool {
		if (current.empty()) return false;
		if (not holds_alternative<scripting::ast::identifier>(current.front().value)) return false;
		if (get<scripting::ast::identifier>(current.front().value).value != "endif") return false;
		return true;
	};
	
	// chomps a new line if available, returns true if it failed
	const auto MISSING_NEW_LINE = [&]() -> bool {
		if (current.empty()) {
			errors.push_back(
				scripting::script_error{.location = code.front().location, .message = "Interrupted conditional"});
			return true;
		}
		auto new_line = current.front();
		if (not holds_alternative<symbol_t>(current.front().value)) {
			errors.push_back(
				scripting::script_error{.location = current.front().location, .message = "Expected new line"});
			return true;
		}
		if (get<symbol_t>(current.front().value) != symbol_t::new_line) {
			errors.push_back(
				scripting::script_error{.location = current.front().location, .message = "Expected new line"});
			return true;
		}
		current = current.subspan(1);
		return false;
	};
	
	if (current.empty()) return FAILURE;
	if (not holds_alternative<scripting::ast::identifier>(current.front().value)) return FAILURE;
	if (get<scripting::ast::identifier>(current.front().value).value != initiator) return FAILURE;
	current = current.subspan(1);
	
	// Read the condition
	auto conditional_node = try_expression(current, errors);
	if (not conditional_node.result) {
		errors.push_back(
			scripting::script_error{.location = code.front().location, .message = "Expected expression in conditional"});
		return FAILURE;
	}
	result.condition = std::make_unique<scripting::ast::expression>(std::move(conditional_node.result.value()));
	current = conditional_node.rest;
	
	if(MISSING_NEW_LINE()) return FAILURE;
	
	if (current.empty()) {
		errors.push_back(
			scripting::script_error{.location = code.front().location, .message = "Interrupted conditional"});
		return FAILURE;
	}
	result.on_condition = std::make_unique<scripting::ast::block>();
	result.on_condition->location = current.front().location;
	
	bool else_mode = false;
	
	while (not endif_found()) {
		const auto error_count = errors.size();
		
		// Handles elseif sequences as nested ifs in the else block
		auto nester = try_conditional(current, errors, "elseif");
		if(nester.result) {
			result.otherwise = std::make_unique<scripting::ast::block>();
			result.otherwise->location = current.front().location;
			result.otherwise->contents.push_back(scripting::ast::statement{
				.location = current.front().location,
				.contents = std::make_unique<scripting::ast::conditional>(std::move(nester.result.value())),
			});
			current = nester.rest;
			return {.result = std::move(result), .rest = current};
		} else if(error_count != errors.size()) {
			return FAILURE;
		}
		
		// Handles code
		if(auto block_contents = try_statement(current, errors); block_contents.result) {
			if(not else_mode) {
				result.on_condition->contents.push_back(std::move(block_contents.result.value()));
			} else {
				result.otherwise->contents.push_back(std::move(block_contents.result.value()));
			}
			current = block_contents.rest;
		} else {
			if(current.empty()) {
				errors.push_back(
					scripting::script_error{.location = code.front().location, .message = "Interrupted conditional"});
				return FAILURE;
			}
			// Handles switching to else mode
			if(
				holds_alternative<scripting::ast::identifier>(current.front().value)
				&& get<scripting::ast::identifier>(current.front().value).value == "else"
				) {
				auto loc = current.front().location;
				current = current.subspan(1);
				if(MISSING_NEW_LINE()) return FAILURE;
				if(else_mode) {
					errors.push_back(
						scripting::script_error{.location = current.front().location, .message = "Repeated else in conditional"});
				} else {
					else_mode = true;
					result.otherwise = std::make_unique<scripting::ast::block>();
					result.otherwise->location = std::move(loc);
				}
			}else {
				errors.push_back(
					scripting::script_error{.location = current.front().location, .message = "Unexpected expression content"});
				return FAILURE;
			}
		}
	}
	
	// checks for endif
	if(endif_found()) {
		current = current.subspan(1);
		if(not current.empty() && MISSING_NEW_LINE()) return FAILURE;
	}
	
	return {.result = std::move(result), .rest = current};
#undef FAILURE
}

parse_result<scripting::ast::while_loop> try_while_loop(const std::span<token> code, std::vector<scripting::script_error>& errors) {
#ifdef FAILURE
	static_assert(false, "Found a macro name FAILURE, halting");
#endif
#define FAILURE {.result = std::nullopt, .rest = code}
	scripting::ast::while_loop result{};
	if(code.empty()) return FAILURE;
	auto current = code;
	result.location = current.front().location;
	
	const auto endwhile_found = [&]() -> bool {
		if (current.empty()) return false;
		if (not holds_alternative<scripting::ast::identifier>(current.front().value)) return false;
		if (get<scripting::ast::identifier>(current.front().value).value != "endwhile") return false;
		return true;
	};
	
	// chomps a new line if available, returns true if it failed
	const auto MISSING_NEW_LINE = [&]() -> bool {
		if (current.empty()) {
			errors.push_back(
				scripting::script_error{.location = code.front().location, .message = "Interrupted while loop"});
			return true;
		}
		auto new_line = current.front();
		if (not holds_alternative<symbol_t>(current.front().value)) {
			errors.push_back(
				scripting::script_error{.location = current.front().location, .message = "Expected new line"});
			return true;
		}
		if (get<symbol_t>(current.front().value) != symbol_t::new_line) {
			errors.push_back(
				scripting::script_error{.location = current.front().location, .message = "Expected new line"});
			return true;
		}
		current = current.subspan(1);
		return false;
	};
	
	if (current.empty()) return FAILURE;
	if (not holds_alternative<scripting::ast::identifier>(current.front().value)) return FAILURE;
	if (get<scripting::ast::identifier>(current.front().value).value != "while") return FAILURE;
	current = current.subspan(1);
	
	// Read the condition
	auto conditional_node = try_expression(current, errors);
	if (not conditional_node.result) {
		errors.push_back(
			scripting::script_error{.location = code.front().location, .message = "Expected expression in while loop"});
		return FAILURE;
	}
	result.condition = std::make_unique<scripting::ast::expression>(std::move(conditional_node.result.value()));
	current = conditional_node.rest;
	
	if(MISSING_NEW_LINE()) return FAILURE;
	
	if (current.empty()) {
		errors.push_back(
			scripting::script_error{.location = code.front().location, .message = "Interrupted while loop"});
		return FAILURE;
	}
	result.on_condition = std::make_unique<scripting::ast::block>();
	result.on_condition->location = current.front().location;
	
	while (not endwhile_found()) {
		const auto error_count = errors.size();
		
		if(error_count != errors.size()) {
			return FAILURE;
		}
		
		// Handles code
		if(auto block_contents = try_statement(current, errors); block_contents.result) {
			result.on_condition->contents.push_back(std::move(block_contents.result.value()));
			current = block_contents.rest;
		} else {
			if(current.empty()) {
				errors.push_back(
					scripting::script_error{.location = code.front().location, .message = "Interrupted while loop"});
				return FAILURE;
			} else {
				errors.push_back(
					scripting::script_error{.location = current.front().location, .message = "Unexpected statement in block"});
				return FAILURE;
			}
		}
	}
	
	// checks for endif
	if(endwhile_found()) {
		current = current.subspan(1);
		if(not current.empty() && MISSING_NEW_LINE()) return FAILURE;
	}
	
	return {.result = std::move(result), .rest = current};
#undef FAILURE
}

parse_result<scripting::ast::paren_expression> try_paren_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::paren_expression paren;
	auto current = code;
	if(current.empty()) return {std::nullopt, code};
	if(not holds_alternative<symbol_t>(current.front().value)) return {std::nullopt, code};
	if(get<symbol_t>(current.front().value) != symbol_t::l_paren) return {std::nullopt, code};
	paren.location = current.front().location;
	current = current.subspan(1);
	
	if(auto [cmd, cmd_rest] = try_command_expr(current, errors); cmd) {
		paren.content = std::make_unique<scripting::ast::command_expression>(std::move(cmd.value()));
		current = cmd_rest;
	} else if(auto [expr, expr_rest] = try_expression(current, errors); expr) {
		paren.content = std::make_unique<scripting::ast::expression>(std::move(expr.value()));
		current = expr_rest;
	} else {
		errors.push_back(
			scripting::script_error{.location = (current.empty() ? paren.location : current.front().location), .message = "Expected either a command or some type of expression"});
		return {std::nullopt, code};
	}
	
	if(current.empty()) {
		errors.push_back(
			scripting::script_error{.location = paren.location, .message = "No matching parenthesis"});
		return {std::nullopt, code};
	}
	if(not holds_alternative<symbol_t>(current.front().value) or get<symbol_t>(current.front().value) != symbol_t::r_paren) {
		errors.push_back(
			scripting::script_error{.location = current.front().location, .message = "No matching parenthesis, expected a closing parenthesis"});
		return {std::nullopt, code};
	}
	current = current.subspan(1);
	
	return {.result = std::move(paren), .rest = current};
}

parse_result<scripting::ast::statement> try_statement(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::statement node;
	auto current = code;
	current = trim_newline(current);
	if(auto [expr, rest] = try_conditional(current, errors); expr) {
		node.contents = std::make_unique<scripting::ast::conditional>(std::move(expr.value()));
		node.location = current.front().location;
		current = rest;
	} else if(auto [expr, rest] = try_command_expr(current, errors); expr) {
		node.contents = std::make_unique<scripting::ast::command_expression>(std::move(expr.value()));
		node.location = current.front().location;
		current = rest;
	} else if(auto [expr, rest] = try_while_loop(current, errors); expr) {
		node.contents = std::make_unique<scripting::ast::while_loop>(std::move(expr.value()));
		node.location = current.front().location;
		current = rest;
	} else return {std::nullopt, code};
	
	current = trim_newline(current);
	
	return {.result = std::move(node), .rest = current};
}

parse_result<scripting::ast::unary_algebraic_expression> try_unary_algebraic_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	constexpr std::array lexer_operators = {symbol_t::binary_not, symbol_t::logical_not};
	constexpr std::array ast_operators = {scripting::ast::operator_t::binary_not, scripting::ast::operator_t::logical_not};
	static_assert(lexer_operators.size() == ast_operators.size());
	
	scripting::ast::unary_algebraic_expression node;
	auto current = code;
	
	if(current.empty()) return {std::nullopt, code};
	if(not holds_alternative<symbol_t>(current.front().value)) return {std::nullopt, code};
	auto res = std::ranges::find(lexer_operators, get<symbol_t>(current.front().value));
	if(res == lexer_operators.end()) return {std::nullopt, code};
	node.location = current.front().location;
	node.op = *(ast_operators.begin() + (res - lexer_operators.begin()));
	current = current.subspan(1);
	
	
	/// TODO: Gives the lowest priority to unaries (aka, they are applied last)
	auto operand = try_expression(current, errors);
	if (not operand.result) {
		errors.push_back(
			scripting::script_error{.location = code.front().location, .message = "Expected expression after unary operator"});
		return {std::nullopt, code};
	}
	node.content = std::make_unique<scripting::ast::expression>(std::move(operand.result.value()));
	current = operand.rest;
	
	return {.result = std::move(node), .rest = current};
}

parse_result<scripting::ast::binary_algebraic_expression> try_binary_algebraic_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	// The two following arrays are the operator mappings
	
	constexpr std::array lexer_operators = {
		symbol_t::divide,
		symbol_t::modulo,
		symbol_t::multiply,
		symbol_t::subtract,
		symbol_t::add,
		symbol_t::bitshift_left,
		symbol_t::bitshift_right,
		symbol_t::rotate_left,
		symbol_t::rotate_right,
		symbol_t::less_than,
		symbol_t::greater_than,
		symbol_t::less_or_equal_than,
		symbol_t::greater_or_equal_than,
		symbol_t::equals,
		symbol_t::different,
		symbol_t::binary_and,
		symbol_t::binary_or,
		symbol_t::binary_xor,
		symbol_t::logical_and,
		symbol_t::logical_or,
	};
	constexpr std::array ast_operators = {
		scripting::ast::operator_t::divide,
		scripting::ast::operator_t::modulo,
		scripting::ast::operator_t::multiply,
		scripting::ast::operator_t::subtract,
		scripting::ast::operator_t::add,
		scripting::ast::operator_t::bitshift_left,
		scripting::ast::operator_t::bitshift_right,
		scripting::ast::operator_t::rotate_left,
		scripting::ast::operator_t::rotate_right,
		scripting::ast::operator_t::less_than,
		scripting::ast::operator_t::greater_than,
		scripting::ast::operator_t::less_or_equal_than,
		scripting::ast::operator_t::greater_or_equal_than,
		scripting::ast::operator_t::equals,
		scripting::ast::operator_t::different,
		scripting::ast::operator_t::binary_and,
		scripting::ast::operator_t::binary_or,
		scripting::ast::operator_t::binary_xor,
		scripting::ast::operator_t::logical_and,
		scripting::ast::operator_t::logical_or,
	};
	constexpr std::array ast_precedences = {
		1,
		1,
		1,
		2,
		2,
		3,
		3,
		3,
		3,
		4,
		4,
		4,
		4,
		4,
		4,
		5,
		5,
		5,
		6,
		7,
	};
	static_assert(lexer_operators.size() == ast_operators.size());
	static_assert(ast_precedences.size() == ast_operators.size());
	
	scripting::ast::binary_algebraic_expression node;
	auto current = code;

#ifdef HANDLE_EXPRESSION
	static_assert(false, "Found a macro name HANDLE_EXPRESSION, halting");
#endif
#define HANDLE_EXPRESSION(type) \
	node.lhs = std::make_unique<scripting::ast::expression>(scripting::ast::expression{ \
		.location = current.front().location, \
		.contents = std::make_unique<type>(std::move(expr.value())) \
	}); \
	current = rest;
	
	if(auto [expr, rest] = try_literal_string_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::literal_string_expression)
	} else if(auto [expr, rest] = try_literal_int_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::literal_int_expression)
	} else if(auto [expr, rest] = try_unary_algebraic_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::unary_algebraic_expression)
	} else if(auto [expr, rest] = try_paren_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::paren_expression)
	} else if(auto [expr, rest] = try_variable_expression(current, errors); expr) {
		HANDLE_EXPRESSION(scripting::ast::variable_expression)
	} else {
		return {std::nullopt, code};
	}
#undef HANDLE_EXPRESSION
	
	if(current.empty()) {
		return {std::nullopt, code};
	}
	if(not holds_alternative<symbol_t>(current.front().value)) {
		return {std::nullopt, code};
	}
	auto res = std::ranges::find(lexer_operators, get<symbol_t>(current.front().value));
	if(res == lexer_operators.end()) {
		return {std::nullopt, code};
	}
	auto rhs_idx = (res - lexer_operators.begin());
	node.op = *(ast_operators.begin() + rhs_idx);
	node.location = current.front().location;
	current = current.subspan(1);
	
	auto operand = try_expression(current, errors);
	if (not operand.result) {
		errors.push_back(
			scripting::script_error{.location = node.location, .message = "Expected expression after binary operator"});
		return {std::nullopt, code};
	}
	/// Check if our "large (rhs) bite" has an operation precedence that is bigger and in that case, swap the operations around
	//... We may need to do that iteratively until we risk a priority reversal. This is basically shifting the ast to the left until
	//... the precedence are "heapified" and left associative
	if(std::holds_alternative<std::unique_ptr<scripting::ast::binary_algebraic_expression>>(operand.result.value().contents)) {
		// Must check for precedence reordering
		auto& lhs = std::get<std::unique_ptr<scripting::ast::binary_algebraic_expression>>(operand.result.value().contents);
		auto lhs_it = std::ranges::find(ast_operators, lhs->op);
		auto lhs_idx = lhs_it - ast_operators.begin();
		// >= ensures left associativity
		if(ast_precedences[rhs_idx] <= ast_precedences[lhs_idx]) {
			// Precedence reordering required
			// https://link.excalidraw.com/l/hxPegpAmTX/6d1BYX0rfKU
			node.rhs = std::move(lhs->lhs);
			scripting::ast::binary_algebraic_expression reordered{
				.location = operand.result.value().location,
				.lhs = std::make_unique<scripting::ast::expression>(scripting::ast::expression{
					.location = node.location,
					.contents = std::make_unique<scripting::ast::binary_algebraic_expression>(std::move(node))
				}),
				.op = lhs->op,
				.rhs = std::move(lhs->rhs),
			};
			current = operand.rest;
			return {.result = std::move(reordered), .rest = current};
		}
	}
	// No reordering required
	node.rhs = std::make_unique<scripting::ast::expression>(std::move(operand.result.value()));
	current = operand.rest;
	
	return {.result = std::move(node), .rest = current};
}

parse_result<scripting::ast::variable_expression> try_variable_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::variable_expression node;
	auto current = code;
	
	if(current.empty()) return {std::nullopt, code};
	if(not holds_alternative<scripting::ast::identifier>(current.front().value)) return {std::nullopt, code};
	node.location = current.front().location;
	node.name = get<scripting::ast::identifier>(current.front().value);
	current = current.subspan(1);
	
	return {.result = std::move(node), .rest = current};
}

parse_result<scripting::ast::literal_string_expression> try_literal_string_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::literal_string_expression node;
	auto current = code;
	
	if(current.empty()) return {std::nullopt, code};
	if(not holds_alternative<std::string>(current.front().value)) return {std::nullopt, code};
	node.location = current.front().location;
	node.value = get<std::string>(current.front().value);
	current = current.subspan(1);
	
	return {.result = std::move(node), .rest = current};
}

parse_result<scripting::ast::literal_int_expression> try_literal_int_expression(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::literal_int_expression node;
	auto current = code;
	
	if(current.empty()) return {std::nullopt, code};
	if(not holds_alternative<int32_t>(current.front().value)) return {std::nullopt, code};
	node.location = current.front().location;
	node.value = get<int32_t>(current.front().value);
	current = current.subspan(1);
	
	return {.result = std::move(node), .rest = current};
}

scripting::ast::block scripting::ast::parse(std::span<token> code, std::vector<scripting::script_error>& errors) {
	scripting::ast::block node;
	auto current = trim_newline(code);
	
	while(not current.empty()) {
		auto pre_size = current.size();
		auto [expr, rest] = try_statement(current, errors);
		if(expr) {
			node.contents.push_back(std::move(expr.value()));
			current = rest;
		} else {
			bool progress = false;
			while(not (next_is_newline(current) or current.empty())) {
				current = current.subspan(1);
				progress = true;
			}
			if(not progress && not errors.empty()) {
				return scripting::ast::block{};
			}
			if(not current.empty() && current.size() == pre_size) {
				errors.push_back(script_error{
					.location = current.front().location,
					.message = "Parsing stuck in infinite loop with no progress"
				});
			}
		}
		current = trim_newline(current);
	}
	if(not errors.empty()) {
		return scripting::ast::block{};
	}
	
	return std::move(node);
}