hare

expr.ha (33101B)

---

 // License: MPL-2.0
 // (c) 2021 Alexey Yerin <yyp@disroot.org>
 // (c) 2021 Bor Grošelj Simić <bor.groseljsimic@telemach.net>
 // (c) 2021 Drew DeVault <sir@cmpwn.com>
 // (c) 2021 Ember Sawady <ecs@d2evs.net>
 // (c) 2022 Sebastian <sebastian@sebsite.pw>
 use hare::ast;
 use hare::lex::{ltok};
 use hare::lex;
 use math;
 use types;
 use strings;
 
 // Parses an expression.
 export fn expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const loc = lex::mkloc(lexer);
 	const indirect = try(lexer, ltok::TIMES)? is lex::token;
 
 	// All assignment-op tokens
 	const atoks: []ltok = [
 		ltok::EQUAL, ltok::BANDEQ, ltok::BOREQ, ltok::BXOREQ,
 		ltok::DIVEQ, ltok::LANDEQ, ltok::LOREQ, ltok::LXOREQ,
 		ltok::LSHIFTEQ, ltok::MINUSEQ, ltok::MODEQ, ltok::PLUSEQ,
 		ltok::RSHIFTEQ, ltok::TIMESEQ,
 	];
 
 	const ex: ast::expr = if (indirect) {
 		const ex = cast(lexer, void)?;
 		// Disambiguate between
 		// 	* unary-expression assignment-op expression
 		// and
 		// 	binary-expression
 		yield if (peek(lexer, atoks...)? is lex::token) {
 			yield ex;
 		} else return binarithm(lexer, ast::expr {
 			start = loc,
 			end = lex::prevloc(lexer),
 			expr = ast::unarithm_expr {
 				op = ast::unarithm_op::DEREF,
 				operand = alloc(ex),
 			},
 		}, 0);
 	} else match (peek(lexer, ltok::IF, ltok::FOR,
 			ltok::BREAK, ltok::CONTINUE, ltok::RETURN, ltok::LET,
 			ltok::CONST, ltok::YIELD)?) {
 	case void =>
 		yield binarithm(lexer, void, 0)?;
 	case let tok: lex::token =>
 		yield switch (tok.0) {
 		case ltok::IF =>
 			yield if_expr(lexer)?;
 		case ltok::FOR =>
 			yield for_expr(lexer)?;
 		case ltok::BREAK, ltok::CONTINUE, ltok::RETURN =>
 			yield control(lexer)?;
 		case ltok::LET, ltok::CONST =>
 			yield binding(lexer, false)?;
 		case ltok::YIELD =>
 			yield yield_expr(lexer)?;
 		case => abort(); // Invariant
 		};
 	};
 
 	const tok = match (try(lexer, atoks...)?) {
 	case let tok: lex::token =>
 		yield tok;
 	case =>
 		return ex;
 	};
 
 	synassert(lex::mkloc(lexer),
 		ex.expr is ast::access_expr || ex.expr is ast::slice_expr || indirect,
 		"Expected an object-selector or slice for assignment target")?;
 	const ex = ast::assign_expr {
 		op = switch (tok.0) {
 		case ltok::EQUAL =>
 			yield void;
 		case ltok::BANDEQ =>
 			yield ast::binarithm_op::BAND;
 		case ltok::BOREQ =>
 			yield ast::binarithm_op::BOR;
 		case ltok::BXOREQ =>
 			yield ast::binarithm_op::BXOR;
 		case ltok::DIVEQ =>
 			yield ast::binarithm_op::DIV;
 		case ltok::LANDEQ =>
 			yield ast::binarithm_op::LAND;
 		case ltok::LOREQ =>
 			yield ast::binarithm_op::LOR;
 		case ltok::LSHIFTEQ =>
 			yield ast::binarithm_op::LSHIFT;
 		case ltok::LXOREQ =>
 			yield ast::binarithm_op::LXOR;
 		case ltok::MINUSEQ =>
 			yield ast::binarithm_op::MINUS;
 		case ltok::MODEQ =>
 			yield ast::binarithm_op::MODULO;
 		case ltok::PLUSEQ =>
 			yield ast::binarithm_op::PLUS;
 		case ltok::RSHIFTEQ =>
 			yield ast::binarithm_op::RSHIFT;
 		case ltok::TIMESEQ =>
 			yield ast::binarithm_op::TIMES;
 		},
 		object = alloc(ex),
 		value = alloc(expr(lexer)?),
 		indirect = indirect,
 	};
 
 	return ast::expr {
 		start = loc,
 		end = lex::prevloc(lexer),
 		expr = ex,
 	};
 };
 
 fn assert_expr(lexer: *lex::lexer, is_static: bool) (ast::expr | error) = {
 	const tok = want(lexer, ltok::ABORT, ltok::ASSERT)?;
 
 	let expr = switch (tok.0) {
 	case ltok::ABORT =>
 		want(lexer, ltok::LPAREN)?;
 		const msg: nullable *ast::expr =
 			match (peek(lexer, ltok::RPAREN)?) {
 			case lex::token =>
 				yield null;
 			case =>
 				yield alloc(expr(lexer)?);
 			};
 		want(lexer, ltok::RPAREN)?;
 
 		yield ast::assert_expr {
 			cond      = null,
 			message   = msg,
 			is_static = is_static,
 		};
 	case ltok::ASSERT =>
 		want(lexer, ltok::LPAREN)?;
 		const cond: nullable *ast::expr =
 			alloc(expr(lexer)?);
 		const msg: nullable *ast::expr =
 			match (try(lexer, ltok::COMMA)?) {
 			case lex::token =>
 				yield alloc(expr(lexer)?);
 			case =>
 				yield null;
 			};
 		want(lexer, ltok::RPAREN)?;
 
 		yield ast::assert_expr {
 			cond      = cond,
 			message   = msg,
 			is_static = is_static,
 		};
 	case => abort(); // unreachable
 	};
 
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn alloc_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::ALLOC)?;
 	want(lexer, ltok::LPAREN)?;
 
 	const init = alloc(expr(lexer)?);
 	const expr =
 		switch (want(lexer, ltok::COMMA, ltok::ELLIPSIS, ltok::RPAREN)?.0) {
 		case ltok::COMMA =>
 			const cap = alloc(expr(lexer)?);
 			want(lexer, ltok::RPAREN)?;
 			yield ast::alloc_expr {
 				init = init,
 				form = ast::alloc_form::COPY,
 				capacity = cap,
 			};
 		case ltok::ELLIPSIS =>
 			want(lexer, ltok::RPAREN)?;
 			yield ast::alloc_expr {
 				init = init,
 				form = ast::alloc_form::COPY,
 				capacity = null,
 			};
 		case ltok::RPAREN =>
 			yield ast::alloc_expr {
 				init = init,
 				form = ast::alloc_form::OBJECT,
 				capacity = null,
 			};
 		};
 
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn append_insert_expr(
 	lexer: *lex::lexer,
 	is_static: bool,
 ) (ast::expr | error) = {
 	const tok = want(lexer, ltok::APPEND, ltok::INSERT)?;
 	want(lexer, ltok::LPAREN)?;
 
 	const object = if (tok.0 == ltok::APPEND) objsel(lexer)?
 		else idxexpr(lexer)?;
 	want(lexer, ltok::COMMA)?;
 
 	let variadic: nullable *ast::expr = null;
 	let values: []*ast::expr = [];
 	for (true) {
 		if (try(lexer, ltok::RPAREN)? is lex::token) break;
 
 		const expr = alloc(expr(lexer)?);
 		switch (want(lexer, ltok::COMMA, ltok::ELLIPSIS, ltok::RPAREN)?.0) {
 		case ltok::COMMA =>
 			append(values, expr);
 		case ltok::ELLIPSIS =>
 			variadic = expr;
 			try(lexer, ltok::COMMA)?;
 			want(lexer, ltok::RPAREN)?;
 			break;
 		case ltok::RPAREN =>
 			append(values, expr);
 			break;
 		case => abort();
 		};
 	};
 
 	synassert(lex::mkloc(lexer), variadic != null || len(values) != 0,
 		"Expected values to append")?;
 
 	const expr = if (tok.0 == ltok::APPEND) ast::append_expr {
 		object = alloc(object),
 		variadic = variadic,
 		values = values,
 		is_static = is_static,
 	} else ast::insert_expr {
 		object = alloc(object),
 		variadic = variadic,
 		values = values,
 		is_static = is_static,
 	};
 
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn measurement(lexer: *lex::lexer) (ast::expr | error) = {
 	const tok = want(lexer, ltok::LEN, ltok::SIZE, ltok::OFFSET)?;
 		want(lexer, ltok::LPAREN)?;
 	const expr = switch (tok.0) {
 	case ltok::LEN =>
 		yield alloc(expr(lexer)?): ast::len_expr;
 	case ltok::SIZE =>
 		yield alloc(_type(lexer)?): ast::size_expr;
 	case ltok::OFFSET =>
 		yield alloc(expr(lexer)?): ast::offset_expr;
 	};
 	want(lexer, ltok::RPAREN)?;
 
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn binarithm(
 	lexer: *lex::lexer,
 	lvalue: (ast::expr | void),
 	i: int,
 ) (ast::expr | error) = {
 	// Precedence climbing parser
 	// https://en.wikipedia.org/wiki/Operator-precedence_parser
 	let lvalue = match (lvalue) {
 	case void =>
 		yield cast(lexer, void)?;
 	case let expr: ast::expr =>
 		yield expr;
 	};
 
 	let tok = lex::lex(lexer)?;
 	for (let j = precedence(tok); j >= i; j = precedence(tok)) {
 		const op = binop_for_tok(tok);
 
 		let rvalue = cast(lexer, void)?;
 		tok = lex::lex(lexer)?;
 
 		for (let k = precedence(tok); k > j; k = precedence(tok)) {
 			lex::unlex(lexer, tok);
 			rvalue = binarithm(lexer, rvalue, k)?;
 			tok = lex::lex(lexer)?;
 		};
 
 		const expr = ast::expr {
 			start = lvalue.start,
 			end = lex::prevloc(lexer),
 			expr = ast::binarithm_expr {
 				op = op,
 				lvalue = alloc(lvalue),
 				rvalue = alloc(rvalue),
 			},
 		};
 		lvalue = expr;
 	};
 
 	lex::unlex(lexer, tok);
 	return lvalue;
 };
 
 fn binding_unpack(lexer: *lex::lexer) (ast::binding_unpack | error) = {
 	let fields: ast::binding_unpack = [];
 	for (true) {
 		const (tok, value, _) = want(lexer, ltok::NAME,
 			ltok::UNDERSCORE)?;
 		if (tok == ltok::UNDERSCORE) {
 			append(fields, void);
 		} else {
 			append(fields, value as str);
 		};
 		if (len(fields) == 1) {
 			want(lexer, ltok::COMMA)?;
 		} else {
 			match (try(lexer, ltok::COMMA)?) {
 			case void => break;
 			case lex::token => void;
 			};
 		};
 	};
 	want(lexer, ltok::RPAREN)?;
 	return fields;
 };
 
 fn binding(lexer: *lex::lexer, is_static: bool) (ast::expr | error) = {
 	const loc = lex::mkloc(lexer);
 	const is_const = want(lexer, ltok::LET, ltok::CONST)?.0 == ltok::CONST;
 
 	let bindings: []ast::binding = [];
 	for (true) {
 		const (tok, value, _) = want(lexer, ltok::NAME, ltok::LPAREN)?;
 		const name = switch (tok) {
 		case ltok::NAME =>
 			yield value as str;
 		case ltok::LPAREN =>
 			yield binding_unpack(lexer)?;
 		case => abort();
 		};
 		const btype: nullable *ast::_type =
 			if (try(lexer, ltok::COLON)? is lex::token) {
 				yield alloc(_type(lexer)?);
 			} else null;
 		want(lexer, ltok::EQUAL)?;
 		const init = alloc(expr(lexer)?);
 		append(bindings, ast::binding {
 			name = name,
 			_type = btype,
 			init = init,
 		});
 		match (try(lexer, ltok::COMMA)?) {
 		case void => break;
 		case lex::token => void;
 		};
 	};
 
 	return ast::expr {
 		start = loc,
 		end = lex::prevloc(lexer),
 		expr = ast::binding_expr {
 			is_static = is_static,
 			is_const = is_const,
 			bindings = bindings,
 		},
 	};
 };
 
 fn builtin(lexer: *lex::lexer) (ast::expr | error) = {
 	const tok = match (peek(lexer, ltok::ALLOC, ltok::APPEND, ltok::FREE,
 		ltok::DELETE, ltok::ABORT, ltok::ASSERT, ltok::INSERT,
 		ltok::STATIC, ltok::SIZE, ltok::LEN, ltok::OFFSET,
 		ltok::DEFER, ltok::VASTART, ltok::VAARG, ltok::VAEND)?) {
 	case let tok: lex::token =>
 		yield tok;
 	case void =>
 		return postfix(lexer, void);
 	};
 	switch (tok.0) {
 	case ltok::ALLOC =>
 		return alloc_expr(lexer);
 	case ltok::APPEND, ltok::INSERT =>
 		return append_insert_expr(lexer, false);
 	case ltok::DELETE =>
 		return delete_expr(lexer, false);
 	case ltok::FREE =>
 		return free_expr(lexer);
 	case ltok::ABORT, ltok::ASSERT =>
 		return assert_expr(lexer, false);
 	case ltok::STATIC =>
 		want(lexer, ltok::STATIC)?;
 		let tok = match (peek(lexer, ltok::LET, ltok::CONST,
 			ltok::ABORT, ltok::ASSERT, ltok::APPEND, ltok::INSERT,
 			ltok::DELETE)?) {
 		case let tok: lex::token =>
 			yield tok;
 		case void =>
 			// TODO: The following is lame:
 			return syntaxerr(tok.2, "Expected let, const, or assert");
 		};
 		switch (tok.0) {
 		case ltok::LET, ltok::CONST =>
 			return binding(lexer, true);
 		case ltok::ABORT, ltok::ASSERT =>
 			return assert_expr(lexer, true);
 		case ltok::APPEND, ltok::INSERT =>
 			return append_insert_expr(lexer, true);
 		case ltok::DELETE =>
 			return delete_expr(lexer, true);
 		case => abort();
 		};
 	case ltok::SIZE, ltok::LEN, ltok::OFFSET =>
 		return measurement(lexer);
 	case ltok::DEFER =>
 		want(lexer, ltok::DEFER)?;
 		let expr = alloc(expr(lexer)?);
 		return ast::expr {
 			start = tok.2,
 			end = lex::prevloc(lexer),
 			expr = expr: ast::defer_expr,
 		};
 	case ltok::VASTART =>
 		want(lexer, ltok::VASTART)?;
 		want(lexer, ltok::LPAREN)?;
 		want(lexer, ltok::RPAREN)?;
 		return ast::expr {
 			start = tok.2,
 			end = lex::prevloc(lexer),
 			expr = void: ast::vastart_expr: ast::variadic_expr,
 		};
 	case ltok::VAARG =>
 		want(lexer, ltok::VAARG)?;
 		want(lexer, ltok::LPAREN)?;
 		const expr = alloc(expr(lexer)?);
 		want(lexer, ltok::RPAREN)?;
 		return ast::expr {
 			start = tok.2,
 			end = lex::prevloc(lexer),
 			expr = expr: ast::vaarg_expr: ast::variadic_expr,
 		};
 	case ltok::VAEND =>
 		want(lexer, ltok::VAEND)?;
 		want(lexer, ltok::LPAREN)?;
 		const expr = alloc(expr(lexer)?);
 		want(lexer, ltok::RPAREN)?;
 		return ast::expr {
 			start = tok.2,
 			end = lex::prevloc(lexer),
 			expr = expr: ast::vaend_expr: ast::variadic_expr,
 		};
 	case => abort(); // Invariant
 	};
 };
 
 fn call(lexer: *lex::lexer, lvalue: ast::expr) (ast::expr | error) = {
 	let args: []*ast::expr = [];
 	let variadic = false;
 
 	for (true) {
 		match (try(lexer, ltok::RPAREN)?) {
 		case lex::token => break;
 		case void => void;
 		};
 
 		append(args, alloc(expr(lexer)?));
 
 		match (try(lexer, ltok::ELLIPSIS)?) {
 		case lex::token =>
 			variadic = true;
 			try(lexer, ltok::COMMA)?;
 			want(lexer, ltok::RPAREN)?;
 			break;
 		case void => void;
 		};
 
 		switch (want(lexer, ltok::COMMA, ltok::RPAREN)?.0) {
 		case ltok::RPAREN => break;
 		case => void;
 		};
 	};
 
 	return ast::expr {
 		start = lvalue.start,
 		end = lex::prevloc(lexer),
 		expr = ast::call_expr {
 			lvalue = alloc(lvalue),
 			variadic = variadic,
 			args = args,
 		},
 	};
 };
 
 fn cast(lexer: *lex::lexer, lvalue: (ast::expr | void)) (ast::expr | error) = {
 	const lvalue = match (lvalue) {
 	case void =>
 		yield unarithm(lexer)?;
 	case let e: ast::expr =>
 		yield e;
 	};
 	const tok = match (try(lexer, ltok::COLON, ltok::AS, ltok::IS)?) {
 	case void =>
 		return lvalue;
 	case let tok: lex::token =>
 		yield tok.0;
 	};
 	const kind = switch (tok) {
 	case ltok::COLON =>
 		yield ast::cast_kind::CAST;
 	case ltok::AS =>
 		yield ast::cast_kind::ASSERTION;
 	case ltok::IS =>
 		yield ast::cast_kind::TEST;
 	case => abort();
 	};
 	let typ = alloc(_type(lexer)?);
 	return cast(lexer, ast::expr {
 		start = lvalue.start,
 		end = lex::prevloc(lexer),
 		expr = ast::cast_expr {
 			kind = kind,
 			value = alloc(lvalue),
 			_type = typ,
 		},
 	})?;
 };
 
 fn constant(lexer: *lex::lexer) (ast::expr | error) = {
 	const tok = want(lexer)?;
 	const expr: ast::constant_expr = switch (tok.0) {
 	case ltok::LIT_RUNE, ltok::LIT_STR =>
 		yield tok.1 as (rune | str);
 	case ltok::LIT_U8, ltok::LIT_U16, ltok::LIT_U32, ltok::LIT_U64,
 		ltok::LIT_UINT, ltok::LIT_SIZE =>
 		yield ast::number_constant {
 			suff = tok.0,
 			value = tok.1 as u64,
 			sign = false,
 		};
 	case ltok::LIT_I8, ltok::LIT_I16, ltok::LIT_I32, ltok::LIT_I64,
 		ltok::LIT_INT =>
 		const n = tok.1 as u64;
 		yield ast::number_constant {
 			suff = tok.0,
 			value = n: i64,
 			sign = false,
 		};
 	case ltok::LIT_ICONST =>
 		const n = tok.1 as u64;
 		yield ast::number_constant {
 			suff = tok.0,
 			value = if (n <= types::I64_MAX: u64) n: i64 else n,
 			sign = false,
 		};
 	case ltok::LIT_F32, ltok::LIT_F64, ltok::LIT_FCONST =>
 		yield ast::number_constant {
 			suff = tok.0,
 			value = tok.1 as f64,
 			sign = false,
 		};
 	case ltok::VOID =>
 		yield void;
 	case ltok::TRUE =>
 		yield true;
 	case ltok::FALSE =>
 		yield false;
 	case ltok::NULL =>
 		yield ast::_null;
 	case =>
 		return syntaxerr(lex::mkloc(lexer), "Expected constant expression");
 	};
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn control(lexer: *lex::lexer) (ast::expr | error) = {
 	let tok = want(lexer, ltok::BREAK, ltok::CONTINUE, ltok::RETURN)?;
 	let label = if (tok.0 == ltok::BREAK || tok.0 == ltok::CONTINUE) {
 		yield match (try(lexer, ltok::COLON)?) {
 		case lex::token =>
 			yield want(lexer, ltok::NAME)?.1 as str;
 		case void =>
 			yield "";
 		};
 	} else "";
 	const expr = switch (tok.0) {
 	case ltok::BREAK =>
 		yield label: ast::break_expr;
 	case ltok::CONTINUE =>
 		yield label: ast::continue_expr;
 	case ltok::RETURN =>
 		yield match (peek(lexer, ltok::COMMA,
 			ltok::SEMICOLON, ltok::EOF)?) {
 		case void =>
 			yield alloc(expr(lexer)?): ast::return_expr;
 		case lex::token =>
 			yield null: ast::return_expr;
 		};
 	};
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn delete_expr(lexer: *lex::lexer, is_static: bool) (ast::expr | error) = {
 	const start = want(lexer, ltok::DELETE)?;
 	want(lexer, ltok::LPAREN)?;
 	const expr = alloc(postfix(lexer, void)?);
 	// TODO: Assert that this was an indexing expression
 	want(lexer, ltok::RPAREN)?;
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::delete_expr {
 			object = expr,
 			is_static = is_static,
 		},
 	};
 };
 
 fn compound_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	let items: []*ast::expr = [];
 
 	const start = want(lexer, ltok::LBRACE, ltok::COLON)?;
 	const label = switch (start.0) {
 	case ltok::COLON =>
 		const tok = want(lexer, ltok::NAME)?;
 		want(lexer, ltok::LBRACE)?;
 		yield tok.1 as str;
 	case =>
 		yield "";
 	};
 
 	for (let more = true; more) {
 		const item = match (peek(lexer, ltok::RBRACE)?) {
 		case lex::token => break;
 		case void =>
 			yield expr(lexer)?;
 		};
 		append(items, alloc(item));
 		want(lexer, ltok::SEMICOLON)?;
 	};
 
 	want(lexer, ltok::RBRACE)?;
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::compound_expr {
 			exprs = items,
 			label = label,
 		},
 	};
 };
 
 fn for_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const tok = want(lexer, ltok::FOR)?;
 	want(lexer, ltok::LPAREN)?;
 
 	const bindings: nullable *ast::expr =
 		match (peek(lexer, ltok::LET, ltok::CONST, ltok::STATIC)?) {
 		case void =>
 			yield null;
 		case let tok: lex::token =>
 			let is_static = if (tok.0 == ltok::STATIC) {
 				want(lexer, ltok::STATIC)?;
 				yield true;
 			} else false;
 			const bindings = alloc(binding(lexer, is_static)?);
 			want(lexer, ltok::SEMICOLON)?;
 			yield bindings;
 		};
 	const cond = alloc(expr(lexer)?);
 	const afterthought: nullable *ast::expr =
 		match (peek(lexer, ltok::SEMICOLON)?) {
 		case void =>
 			yield null;
 		case lex::token =>
 			want(lexer, ltok::SEMICOLON)?;
 			yield alloc(expr(lexer)?);
 		};
 
 	want(lexer, ltok::RPAREN)?;
 
 	const body = alloc(expr(lexer)?);
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = ast::for_expr {
 			bindings = bindings,
 			cond = cond,
 			afterthought = afterthought,
 			body = body,
 		},
 	};
 };
 
 fn free_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::FREE)?;
 	want(lexer, ltok::LPAREN)?;
 	const expr = alloc(expr(lexer)?);
 	want(lexer, ltok::RPAREN)?;
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = expr: ast::free_expr,
 	};
 };
 
 fn if_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::IF)?;
 	want(lexer, ltok::LPAREN)?;
 	const cond = alloc(expr(lexer)?);
 	want(lexer, ltok::RPAREN)?;
 	const tbranch = alloc(expr(lexer)?);
 	const fbranch: nullable *ast::expr = match (try(lexer, ltok::ELSE)?) {
 	case void =>
 		yield null;
 	case lex::token =>
 		yield alloc(expr(lexer)?);
 	};
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::if_expr {
 			cond = cond,
 			tbranch = tbranch,
 			fbranch = fbranch,
 		},
 	};
 };
 
 fn indexing(lexer: *lex::lexer, lvalue: ast::expr) (ast::expr | error) = {
 	let is_slice = false;
 	let start: nullable *ast::expr = null, end: nullable *ast::expr = null;
 
 	if (try(lexer, ltok::SLICE)? is lex::token) {
 		is_slice = true;
 	} else {
 		start = alloc(expr(lexer)?);
 	};
 	if (!is_slice && try(lexer, ltok::SLICE)? is lex::token) {
 		is_slice = true;
 	};
 	if (is_slice && peek(lexer, ltok::RBRACKET)? is void) {
 		end = alloc(expr(lexer)?);
 	};
 
 	want(lexer, ltok::RBRACKET)?;
 	return ast::expr {
 		start = lvalue.start,
 		end = lex::prevloc(lexer),
 		expr = if (is_slice) ast::slice_expr {
 			object = alloc(lvalue),
 			start = start,
 			end = end,
 		} else ast::access_index {
 			object = alloc(lvalue),
 			index = {
 				assert(end == null);
 				yield start as *ast::expr;
 			},
 		},
 	};
 };
 
 fn objsel(lexer: *lex::lexer) (ast::expr | error) = {
 	let expr = postfix(lexer, void)?;
 	synassert(lex::mkloc(lexer), expr.expr is ast::access_expr,
 		"Expected object selector")?;
 	return expr;
 };
 
 fn idxexpr(lexer: *lex::lexer) (ast::expr | error) = {
 	const expr = postfix(lexer, void)?;
 	synassert(lex::mkloc(lexer), expr.expr is ast::access_expr
 		&& expr.expr as ast::access_expr is ast::access_index,
 		"Expected indexing expression")?;
 	return expr;
 };
 
 fn plain_expression(lexer: *lex::lexer) (ast::expr | error) = {
 	let tok = peek(lexer)? as lex::token;
 	if (tok.0 >= ltok::LIT_U8 && tok.0 <= ltok::LAST_LITERAL) {
 		return constant(lexer);
 	};
 	switch (tok.0) {
 	case ltok::TRUE, ltok::FALSE, ltok::NULL, ltok::VOID =>
 		return constant(lexer);
 	case ltok::LBRACKET =>
 		return plain_array(lexer)?;
 	case ltok::STRUCT =>
 		let s = plain_struct(lexer, [])?;
 		return ast::expr {
 			start = tok.2,
 			end = lex::prevloc(lexer),
 			expr = s,
 		};
 	case ltok::LPAREN =>
 		want(lexer, ltok::LPAREN)?;
 		let ex = expr(lexer)?;
 		switch (want(lexer, ltok::RPAREN, ltok::COMMA)?.0) {
 		case ltok::RPAREN =>
 			return ex;
 		case ltok::COMMA =>
 			return plain_tuple(lexer, ex, tok.2)?;
 		case => abort();
 		};
 	case ltok::NAME =>
 		let id = ident(lexer)?;
 		match (peek(lexer, ltok::LBRACE)?) {
 		case void =>
 			return ast::expr {
 				start = tok.2,
 				end = lex::prevloc(lexer),
 				expr = id: ast::access_identifier,
 			};
 		case lex::token =>
 			let s = plain_struct(lexer, id)?;
 			return ast::expr {
 				start = tok.2,
 				end = lex::prevloc(lexer),
 				expr = s,
 			};
 		};
 	case =>
 		return syntaxerr(lex::mkloc(lexer),
 			"Unexpected {}, was expecting an expression",
 			lex::tokstr(tok));
 	};
 };
 
 fn plain_array(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::LBRACKET)?;
 
 	let values: []*ast::expr = [];
 	let expand = false;
 	for (true) {
 		match (try(lexer, ltok::RBRACKET)?) {
 		case lex::token => break;
 		case void => void;
 		};
 
 		append(values, alloc(expr(lexer)?));
 
 		match (try(lexer, ltok::COMMA, ltok::ELLIPSIS)?) {
 		case void =>
 			want(lexer, ltok::RBRACKET)?;
 			break;
 		case let tok: lex::token =>
 			switch (tok.0) {
 			case ltok::ELLIPSIS =>
 				expand = true;
 				try(lexer, ltok::COMMA)?;
 				want(lexer, ltok::RBRACKET)?;
 				break;
 			case ltok::COMMA => void;
 			case => abort();
 			};
 		};
 	};
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::array_constant {
 			expand = expand,
 			values = values,
 		},
 	};
 };
 
 fn plain_struct(
 	lexer: *lex::lexer,
 	alias: ast::ident,
 ) (ast::struct_constant | error) = {
 	if (len(alias) == 0) {
 		want(lexer, ltok::STRUCT)?;
 	};
 	want(lexer, ltok::LBRACE)?;
 
 	let autofill = false;
 	let fields: [](ast::struct_value | *ast::struct_constant) = [];
 	for (true) {
 		const tok = want(lexer, ltok::ELLIPSIS,
 			ltok::NAME, ltok::STRUCT)?;
 		switch (tok.0) {
 		case ltok::ELLIPSIS =>
 			synassert(lex::mkloc(lexer), len(alias) != 0,
 				"Cannot use auto-fill with anonymous struct")?;
 			autofill = true;
 			try(lexer, ltok::COMMA)?;
 			want(lexer, ltok::RBRACE)?;
 			break;
 		case ltok::NAME, ltok::STRUCT =>
 			lex::unlex(lexer, tok);
 			append(fields, struct_field(lexer)?);
 		};
 
 		switch (want(lexer, ltok::COMMA, ltok::RBRACE)?.0) {
 		case ltok::RBRACE => break;
 		case ltok::COMMA =>
 			if (try(lexer, ltok::RBRACE)? is lex::token) {
 				break;
 			};
 		};
 	};
 
 	return ast::struct_constant {
 		autofill = autofill,
 		alias = alias,
 		fields = fields,
 	};
 };
 
 fn struct_field(
 	lexer: *lex::lexer,
 ) (ast::struct_value | *ast::struct_constant | error) = {
 	const tok = want(lexer, ltok::NAME, ltok::STRUCT)?;
 	switch (tok.0) {
 	case ltok::NAME =>
 		const name = strings::dup(tok.1 as str);
 		const tok = match (try(lexer, ltok::COLON,
 			ltok::DOUBLE_COLON, ltok::EQUAL)?) {
 		case let tok: lex::token =>
 			yield tok;
 		case void =>
 			let id: ast::ident = alloc([name]);
 			return alloc(plain_struct(lexer, id)?);
 		};
 
 		switch (tok.0) {
 		case ltok::COLON =>
 			const _type = alloc(_type(lexer)?);
 			want(lexer, ltok::EQUAL)?;
 			const init = alloc(expr(lexer)?);
 			return ast::struct_value {
 				name = name,
 				_type = _type,
 				init = init,
 			};
 		case ltok::DOUBLE_COLON =>
 			let id: ast::ident = alloc([name]);
 			let rest = ident(lexer)?;
 			append(id, rest...);
 			return alloc(plain_struct(lexer, id)?);
 		case ltok::EQUAL =>
 			return ast::struct_value {
 				name = name,
 				_type = null,
 				init = alloc(expr(lexer)?),
 			};
 		case => abort(); // Invariant
 		};
 	case ltok::STRUCT =>
 		lex::unlex(lexer, tok);
 		return alloc(plain_struct(lexer, [])?);
 	case => abort(); // Invariant
 	};
 };
 
 fn plain_tuple(
 	lexer: *lex::lexer,
 	ex: ast::expr,
 	start: lex::location
 ) (ast::expr | error) = {
 	let values: []*ast::expr = [];
 	append(values, alloc(ex));
 
 	for (true) {
 		match (try(lexer, ltok::RPAREN)?) {
 		case lex::token => break;
 		case void => void;
 		};
 
 		append(values, alloc(expr(lexer)?));
 
 		match (try(lexer, ltok::COMMA)?) {
 		case lex::token => void;
 		case void =>
 			want(lexer, ltok::RPAREN)?;
 			break;
 		};
 	};
 
 	return ast::expr {
 		start = start,
 		end = lex::prevloc(lexer),
 		expr = values: ast::tuple_constant,
 	};
 };
 
 fn postfix(lexer: *lex::lexer, lvalue: (ast::expr | void)) (ast::expr | error) = {
 	let lvalue = match (lvalue) {
 	case void =>
 		yield plain_expression(lexer)?;
 	case let ex: ast::expr =>
 		yield ex;
 	};
 
 	let tok = match (try(lexer, ltok::LPAREN, ltok::DOT,
 		ltok::LBRACKET, ltok::QUESTION, ltok::LNOT)?) {
 	case void =>
 		return lvalue;
 	case let tok: lex::token =>
 		yield tok;
 	};
 
 	let next = switch (tok.0) {
 	case ltok::LPAREN =>
 		yield call(lexer, lvalue)?;
 	case ltok::DOT =>
 		yield postfix_dot(lexer, lvalue)?;
 	case ltok::LBRACKET =>
 		yield indexing(lexer, lvalue)?;
 	case ltok::QUESTION =>
 		yield ast::expr {
 			start = lvalue.start,
 			end = lex::prevloc(lexer),
 			expr = ast::propagate_expr {
 				is_abort = false,
 				expr = alloc(lvalue),
 			},
 		};
 	case ltok::LNOT =>
 		yield ast::expr {
 			start = lvalue.start,
 			end = lex::prevloc(lexer),
 			expr = ast::propagate_expr {
 				is_abort = true,
 				expr = alloc(lvalue),
 			},
 		};
 	case => abort();
 	};
 
 	return postfix(lexer, next);
 };
 
 fn postfix_dot(
 	lexer: *lex::lexer,
 	lvalue: ast::expr,
 ) (ast::expr | error) = {
 	match (try(lexer, ltok::NAME)?) {
 	case let tok: lex::token =>
 		return ast::expr {
 			start = lvalue.start,
 			end = lex::prevloc(lexer),
 			expr = ast::access_field {
 				object = alloc(lvalue),
 				field = tok.1 as str,
 			},
 		};
 	case void =>
 		let con = constant(lexer)?;
 		let val = con.expr as ast::constant_expr;
 		synassert(lex::mkloc(lexer), val is ast::number_constant,
 			"Expected integer constant")?;
 		let val = val as ast::number_constant;
 		return ast::expr {
 			start = lvalue.start,
 			end = lex::prevloc(lexer),
 			expr = ast::access_tuple {
 				object = alloc(lvalue),
 				value = alloc(con),
 			},
 		};
 	};
 };
 
 fn switch_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::SWITCH)?;
 
 	want(lexer, ltok::LPAREN)?;
 	const value = expr(lexer)?;
 	want(lexer, ltok::RPAREN)?;
 
 	want(lexer, ltok::LBRACE)?;
 
 	let cases: []ast::switch_case = [];
 	for (true) {
 		want(lexer, ltok::CASE)?;
 
 		let opts: []*ast::expr = [];
 		if (try(lexer, ltok::ARROW)? is void) for (true) {
 			append(opts, alloc(expr(lexer)?));
 			switch (want(lexer, ltok::ARROW, ltok::COMMA)?.0) {
 			case ltok::ARROW =>
 				break;
 			case ltok::COMMA =>
 				if (try(lexer, ltok::ARROW)? is lex::token) {
 					break;
 				};
 			};
 		};
 
 		let exprs: []*ast::expr = [];
 		for (peek(lexer, ltok::CASE, ltok::RBRACE)? is void) {
 			append(exprs, alloc(expr(lexer)?));
 			want(lexer, ltok::SEMICOLON)?;
 		};
 
 		append(cases, ast::switch_case {
 			options = opts,
 			exprs = exprs,
 		});
 
 		if (try(lexer, ltok::RBRACE)? is lex::token) {
 			break;
 		};
 	};
 
 	synassert(start.2, len(cases) != 0, "Expected a list of switch cases")?;
 
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::switch_expr {
 			value = alloc(value),
 			cases = cases,
 		},
 	};
 };
 
 fn match_case(lexer: *lex::lexer) (ast::match_case | error) = {
 	let tok = lex::lex(lexer)?;
 	let loc = tok.2;
 	let name: str = "", typ: nullable *ast::_type = null;
 	switch (tok.0) {
 	case ltok::NULL =>
 		typ = alloc(ast::_type {
 			start = loc,
 			end = lex::prevloc(lexer),
 			flags = 0,
 			repr = ast::builtin_type::NULL,
 		});
 	case ltok::LET =>
 		name = want(lexer, ltok::NAME)?.1 as str;
 		want(lexer, ltok::COLON)?;
 		typ = alloc(_type(lexer)?);
 	case ltok::ARROW => void;
 	case =>
 		lex::unlex(lexer, tok);
 		typ = alloc(_type(lexer)?);
 	};
 	want(lexer, ltok::ARROW)?;
 	let exprs: []*ast::expr = [];
 	for (peek(lexer, ltok::CASE, ltok::RBRACE)? is void) {
 		append(exprs, alloc(expr(lexer)?));
 		want(lexer, ltok::SEMICOLON)?;
 	};
 
 	synassert(lex::mkloc(lexer), len(exprs) != 0, "Expected a match case")?;
 
 	return ast::match_case {
 		name = name,
 		_type = typ,
 		exprs = exprs,
 	};
 };
 
 fn match_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::MATCH)?;
 	want(lexer, ltok::LPAREN)?;
 	const value = expr(lexer)?;
 	want(lexer, ltok::RPAREN)?;
 	want(lexer, ltok::LBRACE)?;
 
 	let cases: []ast::match_case = [];
 	let default: []*ast::expr = [];
 	for (true) {
 		want(lexer, ltok::CASE)?;
 
 		match (try(lexer, ltok::ARROW)?) {
 		case let t: lex::token =>
 			if (len(default) != 0) {
 				return syntaxerr(t.2,
 					"More than one default match case");
 			};
 			for (peek(lexer, ltok::CASE, ltok::RBRACE)? is void) {
 				append(default, alloc(expr(lexer)?));
 				want(lexer, ltok::SEMICOLON)?;
 			};
 		case void =>
 			append(cases, match_case(lexer)?);
 		};
 
 		if (try(lexer, ltok::RBRACE)? is lex::token) {
 			break;
 		};
 	};
 
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::match_expr {
 			value   = alloc(value),
 			cases   = cases,
 			default = default,
 		},
 	};
 };
 
 fn unarithm(lexer: *lex::lexer) (ast::expr | error) = {
 	const tok = match (try(lexer,
 		ltok::PLUS, ltok::MINUS, ltok::BNOT,
 		ltok::LNOT, ltok::TIMES, ltok::BAND,
 		ltok::SWITCH, ltok::MATCH, ltok::COLON, ltok::LBRACE)?) {
 	case void =>
 		return builtin(lexer);
 	case let tok: lex::token =>
 		yield switch (tok.0) {
 		case ltok::SWITCH =>
 			lex::unlex(lexer, tok);
 			return switch_expr(lexer);
 		case ltok::MATCH =>
 			lex::unlex(lexer, tok);
 			return match_expr(lexer);
 		case ltok::COLON, ltok::LBRACE =>
 			lex::unlex(lexer, tok);
 			return compound_expr(lexer);
 		case =>
 			yield tok;
 		};
 	};
 
 	const op = switch (tok.0) {
 	case ltok::PLUS =>
 		yield ast::unarithm_op::PLUS;
 	case ltok::MINUS =>
 		yield ast::unarithm_op::MINUS;
 	case ltok::BNOT =>
 		yield ast::unarithm_op::BNOT;
 	case ltok::LNOT =>
 		yield ast::unarithm_op::LNOT;
 	case ltok::TIMES =>
 		yield ast::unarithm_op::DEREF;
 	case ltok::BAND =>
 		yield ast::unarithm_op::ADDR;
 	case => abort();
 	};
 
 	const operand = unarithm(lexer)?;
 	const expr = :blk {
 		if (op == ast::unarithm_op::MINUS) match (operand.expr) {
 		case let c: ast::constant_expr =>
 			match (c) {
 			case let n: ast::number_constant =>
 				let sign = false;
 				const val = match (n.value) {
 				case let i: i64 =>
 					sign = i < 0;
 					yield -i;
 				case let u: u64 => void;
 				case let f: f64 =>
 					sign = math::signf64(f) < 0;
 					yield -f;
 				};
 
 				if (val is void) yield;
 				yield :blk, ast::number_constant {
 					suff = n.suff,
 					value = val as (i64 | f64),
 					sign = sign,
 				}: ast::constant_expr;
 			case => void;
 			};
 		case => void;
 		};
 
 		yield ast::unarithm_expr {
 			op = op,
 			operand = alloc(operand),
 		};
 	};
 	return ast::expr {
 		start = tok.2,
 		end = lex::prevloc(lexer),
 		expr = expr,
 	};
 };
 
 fn yield_expr(lexer: *lex::lexer) (ast::expr | error) = {
 	const start = want(lexer, ltok::YIELD)?;
 	let label = "";
 	let value: nullable *ast::expr = null;
 	match (try(lexer, ltok::SEMICOLON, ltok::COLON, ltok::EOF)?) {
 	case void =>
 		value = alloc(expr(lexer)?);
 	case let t: lex::token =>
 		switch (t.0) {
 		case ltok::SEMICOLON, ltok::EOF =>
 			lex::unlex(lexer, t);
 		case ltok::COLON =>
 			label = want(lexer, ltok::NAME)?.1 as str;
 			match (try(lexer, ltok::COMMA)?) {
 			case void => void;
 			case lex::token =>
 				value = alloc(expr(lexer)?);
 			};
 		};
 	};
 	return ast::expr {
 		start = start.2,
 		end = lex::prevloc(lexer),
 		expr = ast::yield_expr {
 			label = label,
 			value = value,
 		},
 	};
 };
 
 fn binop_for_tok(tok: lex::token) ast::binarithm_op = {
 	switch (tok.0) {
 	case ltok::BAND =>
 		return ast::binarithm_op::BAND;
 	case ltok::BOR =>
 		return ast::binarithm_op::BOR;
 	case ltok::BXOR =>
 		return ast::binarithm_op::BXOR;
 	case ltok::DIV =>
 		return ast::binarithm_op::DIV;
 	case ltok::GT =>
 		return ast::binarithm_op::GT;
 	case ltok::GTEQ =>
 		return ast::binarithm_op::GTEQ;
 	case ltok::LAND =>
 		return ast::binarithm_op::LAND;
 	case ltok::LEQUAL =>
 		return ast::binarithm_op::LEQUAL;
 	case ltok::LESS =>
 		return ast::binarithm_op::LESS;
 	case ltok::LESSEQ =>
 		return ast::binarithm_op::LESSEQ;
 	case ltok::LOR =>
 		return ast::binarithm_op::LOR;
 	case ltok::LSHIFT =>
 		return ast::binarithm_op::LSHIFT;
 	case ltok::LXOR =>
 		return ast::binarithm_op::LXOR;
 	case ltok::MINUS =>
 		return ast::binarithm_op::MINUS;
 	case ltok::MODULO =>
 		return ast::binarithm_op::MODULO;
 	case ltok::NEQUAL =>
 		return ast::binarithm_op::NEQUAL;
 	case ltok::PLUS =>
 		return ast::binarithm_op::PLUS;
 	case ltok::RSHIFT =>
 		return ast::binarithm_op::RSHIFT;
 	case ltok::TIMES =>
 		return ast::binarithm_op::TIMES;
 	case => abort();
 	};
 };
 
 fn precedence(tok: lex::token) int = {
 	switch (tok.0) {
 	case ltok::LOR =>
 		return 0;
 	case ltok::LXOR =>
 		return 1;
 	case ltok::LAND =>
 		return 2;
 	case ltok::LEQUAL, ltok::NEQUAL =>
 		return 3;
 	case ltok::LESS, ltok::LESSEQ, ltok::GT, ltok::GTEQ =>
 		return 4;
 	case ltok::BOR =>
 		return 5;
 	case ltok::BXOR =>
 		return 6;
 	case ltok::BAND =>
 		return 7;
 	case ltok::LSHIFT, ltok::RSHIFT =>
 		return 8;
 	case ltok::PLUS, ltok::MINUS =>
 		return 9;
 	case ltok::TIMES, ltok::DIV, ltok::MODULO =>
 		return 10;
 	case =>
 		return -1;
 	};
 };