#include "../block.h"
#include "../debug.h"
#include "../node.h"
#include "expr.h"

#include <blue/object/string.h>
#include <ivy/lang/lex.h>
#include <ivy/lang/operator.h>
#include <stdio.h>
#include <stdlib.h>

static void print_operand(struct ivy_ast_node *node)
{
	switch (node->n_type) {
	case IVY_AST_IDENT: {
		struct ivy_ast_ident_node *ident
			= (struct ivy_ast_ident_node *)node;
		debug_printf("%s", ident->n_content->t_str);
		break;
	}
	case IVY_AST_INT: {
		struct ivy_ast_int_node *v = (struct ivy_ast_int_node *)node;
		debug_printf("%llu", v->n_value->t_int);
		break;
	}
	case IVY_AST_DOUBLE: {
		struct ivy_ast_double_node *v = (struct ivy_ast_double_node *)node;
		debug_printf("%.2lf", v->n_value->t_double);
		break;
	}
	case IVY_AST_OP: {
		struct ivy_ast_op_node *v = (struct ivy_ast_op_node *)node;
		debug_printf("%s", ivy_operator_id_to_string(v->n_op->op_id));
		break;
	}
	case IVY_AST_MSG: {
		struct ivy_ast_msg_node *v = (struct ivy_ast_msg_node *)node;
		if (v->n_sel->n_msg_name) {
			debug_printf("%s()", v->n_sel->n_msg_name->t_str);
		} else {
			debug_printf("<keyword-msg>");
		}
		break;
	}
	case IVY_AST_STRING: {
		struct ivy_ast_string_node *v = (struct ivy_ast_string_node *)node;
		debug_printf("\"%s\"", v->n_value->t_str);
		break;
	}
	default:
		debug_printf("<node>");
		break;
	}
}

enum ivy_status arith_push_operand(
	struct expr_parser_state *state, struct ivy_token *tok)
{
	switch (tok->t_type) {
	case IVY_TOK_IDENT: {
		struct ivy_ast_ident_node *v
			= (struct ivy_ast_ident_node *)ast_node_create(
				IVY_AST_IDENT);
		v->n_content = tok;
		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_base.n_entry);
		break;
	}
	case IVY_TOK_INT: {
		struct ivy_ast_int_node *v
			= (struct ivy_ast_int_node *)ast_node_create(IVY_AST_INT);
		v->n_value = tok;
		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_base.n_entry);
		break;
	}
	case IVY_TOK_DOUBLE: {
		struct ivy_ast_double_node *v
			= (struct ivy_ast_double_node *)ast_node_create(
				IVY_AST_DOUBLE);
		v->n_value = tok;
		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_base.n_entry);
		break;
	}
	case IVY_TOK_ATOM: {
		struct ivy_ast_atom_node *v
			= (struct ivy_ast_atom_node *)ast_node_create(IVY_AST_ATOM);
		v->n_content = tok;
		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_base.n_entry);
		break;
	}
	case IVY_TOK_STRING: {
		struct ivy_ast_string_node *v
			= (struct ivy_ast_string_node *)ast_node_create(
				IVY_AST_STRING);
		v->n_value = tok;
		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_base.n_entry);
		break;
	}
	case IVY_TOK_SYMBOL: {
		if (tok->t_symbol != IVY_SYM_UNDERSCORE) {
			return IVY_ERR_BAD_SYNTAX;
		}

		struct ivy_ast_node *v = ast_node_create(IVY_AST_DISCARD);
		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_entry);
		break;
	}
	case IVY_TOK_KEYWORD: {
		struct ivy_ast_node *v = NULL;
		switch (tok->t_keyword) {
		case IVY_KW_BREAK:
			v = ast_node_create(IVY_AST_LOOP_BREAK);
			break;
		case IVY_KW_CONTINUE:
			v = ast_node_create(IVY_AST_LOOP_REPEAT);
			break;
		case IVY_KW_TRUE:
			v = ast_node_create(IVY_AST_C_TRUE);
			break;
		case IVY_KW_FALSE:
			v = ast_node_create(IVY_AST_C_FALSE);
			break;
		case IVY_KW_NULL:
			v = ast_node_create(IVY_AST_C_NULL);
			break;
		default:
			return IVY_ERR_BAD_SYNTAX;
		}

		ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)v, tok);
		b_queue_push_back(&state->s_output_queue, &v->n_entry);
		break;
	}
	default:
		return IVY_ERR_BAD_SYNTAX;
	}

	return IVY_OK;
}

static const struct ivy_operator *get_operator_from_token(struct ivy_token *tok)
{
	switch (tok->t_type) {
	case IVY_TOK_SYMBOL:
		return ivy_operator_get_by_token(tok->t_symbol);
	case IVY_TOK_KEYWORD:
		return ivy_operator_get_by_token(tok->t_keyword);
	default:
		return ivy_operator_get_by_token(tok->t_type);
	}
}

static const struct ivy_operator *get_operator_from_node(struct ivy_ast_node *n)
{
	switch (n->n_type) {
	case IVY_AST_OP: {
		struct ivy_ast_op_node *op = (struct ivy_ast_op_node *)n;
		return op->n_op;
	}
	case IVY_AST_MSG:
		return ivy_operator_get_by_id(IVY_OP_MSG);
	default:
		return NULL;
	}
}

static struct ivy_ast_selector_node *unary_selector_from_token(struct ivy_token *tok)
{
	struct ivy_ast_selector_node *sel
		= (struct ivy_ast_selector_node *)ast_node_create(IVY_AST_SELECTOR);
	ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)sel, tok);
	sel->n_msg_name = tok;
	return sel;
}

static struct ivy_ast_node *create_operator_node_from_token(struct ivy_token *tok)
{
	const struct ivy_operator *op = get_operator_from_token(tok);
	if (!op) {
		return NULL;
	}

	if (op->op_id == IVY_OP_MSG) {
		struct ivy_ast_msg_node *new_msg_node
			= (struct ivy_ast_msg_node *)ast_node_create(IVY_AST_MSG);
		new_msg_node->n_sel = unary_selector_from_token(tok);
		ivy_ast_node_set_bounds_from_token(
			(struct ivy_ast_node *)new_msg_node, tok);
		return (struct ivy_ast_node *)new_msg_node;
	}

	struct ivy_ast_op_node *new_op_node
		= (struct ivy_ast_op_node *)ast_node_create(IVY_AST_OP);
	new_op_node->n_op = op;
	ivy_ast_node_set_bounds_from_token((struct ivy_ast_node *)new_op_node, tok);
	return (struct ivy_ast_node *)new_op_node;
}

#ifdef IVY_LANG_DEBUG
static void print_expr_queues(struct expr_parser_state *state)
{
	b_queue_iterator it = {0};

	debug_printf("operators:");
	b_queue_foreach (&it, &state->s_operator_stack) {
		struct ivy_ast_node *n
			= b_unbox(struct ivy_ast_node, it.entry, n_entry);
		debug_printf(" ");
		print_operand(n);
	}

	debug_printf("\noperands:");
	b_queue_foreach (&it, &state->s_output_queue) {
		struct ivy_ast_node *n
			= b_unbox(struct ivy_ast_node, it.entry, n_entry);
		debug_printf(" ");
		print_operand(n);
	}

	debug_printf("\n");
}
#endif

void arith_push_operator(struct expr_parser_state *state, struct ivy_ast_node *node)
{
	const struct ivy_operator *op = get_operator_from_node(node);
	if (!op) {
		return;
	}

	while (true) {
		b_queue_entry *top = b_queue_last(&state->s_operator_stack);
		if (!top) {
			break;
		}

		struct ivy_ast_node *top_node
			= b_unbox(struct ivy_ast_node, top, n_entry);
		const struct ivy_operator *top_op = NULL;

		switch (top_node->n_type) {
		case IVY_AST_OP: {
			struct ivy_ast_op_node *op_node
				= (struct ivy_ast_op_node *)top_node;
			top_op = op_node->n_op;
			break;
		}
		case IVY_AST_MSG: {
			struct ivy_ast_msg_node *msg_node
				= (struct ivy_ast_msg_node *)top_node;
			top_op = ivy_operator_get_by_id(IVY_OP_MSG);
			break;
		}
		default:
			return;
		}

		if (top_op->op_precedence < op->op_precedence
		    || (top_op->op_precedence == op->op_precedence
		        && op->op_associativity != IVY_ASSOCIATIVITY_LEFT)) {
			break;
		}

		b_queue_delete(&state->s_operator_stack, top);
		b_queue_push_back(&state->s_output_queue, top);
	}

	b_queue_push_back(&state->s_operator_stack, &node->n_entry);
#ifdef IVY_LANG_DEBUG
	print_expr_queues(state);
#endif
}

static bool op_node_is_complete(struct ivy_ast_op_node *node)
{
	if (!node->n_op) {
		return false;
	}

	switch (node->n_op->op_arity) {
	case IVY_OP_UNARY:
		return node->n_right != NULL;
	case IVY_OP_BINARY:
		return (node->n_left != NULL && node->n_right != NULL);
	default:
		return false;
	}
}

enum ivy_status expr_finalise_arith(
	struct expr_parser_state *state, struct ivy_ast_node **expr_tree,
	enum ivy_operator_precedence minimum_precedence)
{
	b_queue_iterator it = {0};

	/* first, take all the operators still left on the operator stack and
	 * add them to the output queue.
	 *
	 * since each set of parentheses has its own expression context,
	 * we don't have to handle parentheses here */
	while (true) {
		b_queue_entry *entry = b_queue_pop_back(&state->s_operator_stack);
		if (!entry) {
			break;
		}

		struct ivy_ast_node *node
			= b_unbox(struct ivy_ast_node, entry, n_entry);
		if (!node) {
			/* this should never happen */
			return IVY_ERR_INTERNAL_FAILURE;
		}

		const struct ivy_operator *op = NULL;

		switch (node->n_type) {
		case IVY_AST_OP: {
			struct ivy_ast_op_node *n = (struct ivy_ast_op_node *)node;
			op = n->n_op;
			break;
		}
		case IVY_AST_MSG:
			/* all unary message operators have the same pre-defined
			 * precedence */
			op = ivy_operator_get_by_id(IVY_OP_MSG);
			break;
		default:
			return IVY_ERR_INTERNAL_FAILURE;
		}

		/* if we aren't processing operators below a certain precedence
		 * then leave them on the stack and stop here. */
		if (op->op_precedence < minimum_precedence) {
			b_queue_push_back(&state->s_operator_stack, entry);
			break;
		}

		b_queue_push_back(&state->s_output_queue, entry);
	}

#if 0
	debug_printf("** after linearisation:\n");
	print_expr_queues(state);
#endif

	/* next, step through the output queue and build a tree of ast nodes
	 * representing the expression. the queue is in RPM, where operators
	 * always follow their operands, so a queue of operands is needed
	 * for the conversion. */

	b_queue q = B_QUEUE_INIT;
	b_queue_entry *tmp = NULL;
	b_queue_iterator_begin(&state->s_output_queue, &it);
	int i = 0;

	while (b_queue_iterator_is_valid(&it)) {
		struct ivy_ast_node *item
			= b_unbox(struct ivy_ast_node, it.entry, n_entry);
		b_queue_iterator_erase(&it);

		/* if the node is an operand, just push it to a temporary queue
		 * and come back to it later. */
		if (item->n_type != IVY_AST_OP && item->n_type != IVY_AST_MSG) {
			/* operand */
			b_queue_push_back(&q, &item->n_entry);
			continue;
		}

		const struct ivy_operator *op = NULL;

		if (item->n_type == IVY_AST_MSG) {
			struct ivy_ast_msg_node *msg
				= (struct ivy_ast_msg_node *)item;
			/* if the message has no recipient, it is a unary message,
			 * and the recipient is located on the operand stack.
			 *
			 * if the message DOES have a recipient, it is a
			 * self-contained keyword message, and can be pushed to
			 * the operand queue as-is. */
			if (!msg->n_recipient) {
				tmp = b_queue_pop_back(&q);
				msg->n_recipient = b_unbox(
					struct ivy_ast_node, tmp, n_entry);
			}
			b_queue_push_back(&q, &msg->n_base.n_entry);
			continue;
		}

		struct ivy_ast_op_node *op_node = (struct ivy_ast_op_node *)item;
		/* if an operator node is already complete (i.e. it already has
		 * all the operands it needs, it can be pushed to the operand
		 * queue as-is */
		if (op_node_is_complete(op_node)) {
			b_queue_push_back(&q, &item->n_entry);
			continue;
		}

		/* otherwise, pop the relevant operands from the operand
		 * queue... */
		op = op_node->n_op;
		tmp = b_queue_pop_back(&q);
		op_node->n_right = b_unbox(struct ivy_ast_node, tmp, n_entry);

		if (op_node->n_right) {
			op_node->n_right->n_parent = (struct ivy_ast_node *)op_node;

			ivy_ast_node_extend_bounds_recursive(
				(struct ivy_ast_node *)op_node,
				(struct ivy_ast_node *)tmp);
		}

		if (op->op_arity == IVY_OP_BINARY) {
			tmp = b_queue_pop_back(&q);
			op_node->n_left
				= b_unbox(struct ivy_ast_node, tmp, n_entry);

			if (op_node->n_left) {
				op_node->n_left->n_parent
					= (struct ivy_ast_node *)op_node;

				ivy_ast_node_extend_bounds_recursive(
					(struct ivy_ast_node *)op_node,
					(struct ivy_ast_node *)tmp);
			}
		}

		/* ...and push the newly-completed operator node to the operand
		 * queue */
		b_queue_push_back(&q, &op_node->n_base.n_entry);
	}

#if 0
	debug_printf("** after hierarchisation:\n");
	print_expr_queues(state);
#endif

	/* if we are not processing operators below a certain precedence,
	 * i.e. when determining the recipient of a keyword-message), these
	 * operators will still be on the parser state's operator stack, but
	 * their operands have just been moved to the temporary operand stack
	 * used above. move them back to the parser state's output queue here
	 * so they can be used later. */
	b_queue_foreach (&it, &state->s_operator_stack) {
		b_queue_entry *entry = b_queue_pop_front(&q);
		if (!entry) {
			return IVY_ERR_INTERNAL_FAILURE;
		}

		b_queue_push_back(&state->s_output_queue, entry);
	}

#if 0
	debug_printf("** after de-linearisation:\n");
	print_expr_queues(state);
	ivy_ast_node_print(*expr_tree);
	debug_printf("------\n");
#endif

	/* the final node remaining on the temp operand stack is the root node
	 * of the new expression tree */
	tmp = b_queue_pop_back(&q);
	*expr_tree = b_unbox(struct ivy_ast_node, tmp, n_entry);

	return IVY_OK;
}

struct token_parse_result arith_parse_fstring(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type == EXPR_TYPE_STMT) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_prev_component == EXPR_CMP_OPERAND) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_type = EXPR_TYPE_ARITH;
	state->s_prev_component = EXPR_CMP_OPERAND;
	state->s_prev_token = tok->t_type;

	parser_push_state(ctx, IVY_AST_FSTRING, 0);

	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_operand(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type == EXPR_TYPE_STMT) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
		/* this is an unlabeled complex message arg */
		if (state->s_prev_token != IVY_SYM_COMMA
		    && state->s_prev_token != IVY_SYM_LEFT_PAREN) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		struct ivy_token *empty_label = malloc(sizeof *empty_label);
		if (!empty_label) {
			return PARSE_RESULT(IVY_ERR_NO_MEMORY, 0);
		}
		memset(empty_label, 0x0, sizeof *empty_label);
		empty_label->t_type = IVY_TOK_LABEL;

		b_queue_push_back(&state->s_labels, &empty_label->t_entry);

		struct expr_parser_state *arg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
		expr_copy_terminators(state, arg_expr);
		expr_add_terminator(arg_expr, IVY_SYM_COMMA);
		arg_expr->s_sub_type = EXPR_SUBTYPE_COMPLEX_ARG;
		arg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

		return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
	}

	if (state->s_prev_component == EXPR_CMP_OPERAND) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_type = EXPR_TYPE_ARITH;

	arith_push_operand(state, tok);
	// print_expr_queues(state);
	state->s_prev_component = EXPR_CMP_OPERAND;
	state->s_prev_token = tok->t_type;

	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_operator(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	unsigned short tok_id = 0;

	switch (tok->t_type) {
	case IVY_TOK_SYMBOL:
		tok_id = tok->t_symbol;
		state->s_prev_token = tok->t_symbol;
		break;
	case IVY_TOK_KEYWORD:
		tok_id = tok->t_keyword;
		state->s_prev_token = tok->t_keyword;
		break;
	default:
		tok_id = tok->t_type;
		state->s_prev_token = tok->t_type;
		break;
	}

	if (expr_terminates_at_token(state, tok_id)) {
		/* treat this as a statement terminator. */
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags |= PARSE_REPEAT_TOKEN;
		return result;
	}

	struct ivy_ast_node *op = create_operator_node_from_token(tok);
	if (!op) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	arith_push_operator(state, op);
	state->s_prev_component = EXPR_CMP_OPERATOR;

#ifdef IVY_LANG_DEBUG
	print_expr_queues(state);
#endif
	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_in(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (expr_terminates_at_token(state, IVY_KW_IN)) {
		/* treat this as a statement terminator. */
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags |= PARSE_REPEAT_TOKEN;
		return result;
	}

	return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
}

struct token_parse_result arith_parse_do(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	bool terminator = false;
	if (expr_terminates_at_token(state, IVY_KW_DO)) {
		terminator = true;
	}

	if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_MSG
	    || state->s_sub_type == EXPR_SUBTYPE_KEYWORD_ARG) {
		terminator = true;
	}

	if (terminator) {
		state->s_prev_token = IVY_KW_DO;
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags = PARSE_REPEAT_TOKEN;
		return result;
	}

	/* next component will be a block. */
	struct block_parser_state *block
		= (struct block_parser_state *)parser_push_state(
			ctx, IVY_AST_BLOCK, 0);
	/* set the sub-expression depth to be non-zero so the expression parser
	 * doesn't consume the expression separator. */

	state->s_prev_token = IVY_KW_DO;

	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_ident(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	struct token_parse_result result;

	if (state->s_sub_type == EXPR_SUBTYPE_MSG) {
		if (state->s_prev_component == EXPR_CMP_MSG) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		result = arith_parse_operator(ctx, tok);
		state->s_prev_component = EXPR_CMP_MSG;
		return result;
	}

	if (state->s_prev_component == EXPR_CMP_OPERAND
	    || state->s_prev_component == EXPR_CMP_MSG) {
		result = arith_parse_operator(ctx, tok);
		state->s_prev_component = EXPR_CMP_MSG;
	} else {
		result = arith_parse_operand(ctx, tok);
	}

	return result;
}

struct token_parse_result arith_parse_left_paren(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type == EXPR_TYPE_NONE) {
		state->s_type = EXPR_TYPE_ARITH;
	}

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_prev_token == IVY_TOK_IDENT) {
		/* this might be the opening parenthesis for a complex message. */
		b_queue_entry *msg_entry = b_queue_last(&state->s_operator_stack);
		struct ivy_ast_node *msg
			= b_unbox(struct ivy_ast_node, msg_entry, n_entry);

		if (!msg || msg->n_type != IVY_AST_MSG) {
			/* this is not a complex message, it's probably a
			 * call-operator */
			goto not_complex_msg;
		}

		b_queue_pop_back(&state->s_operator_stack);

		struct expr_parser_state *msg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);

		expr_add_terminator(msg_expr, IVY_SYM_COMMA);
		msg_expr->s_msg = (struct ivy_ast_msg_node *)msg;
		msg_expr->s_sub_type = EXPR_SUBTYPE_COMPLEX_MSG;
		msg_expr->s_type = EXPR_TYPE_ARITH;
		msg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

		msg_expr->s_prev_token = state->s_prev_token = IVY_SYM_LEFT_PAREN;

		return PARSE_RESULT(IVY_OK, 0);
	}

not_complex_msg:
	if (state->s_prev_component == EXPR_CMP_OPERAND) {
		/* this is the opening parenthesis for a call-operator */
		struct ivy_ast_msg_node *msg
			= (struct ivy_ast_msg_node *)ast_node_create(IVY_AST_MSG);
		msg->n_sel = unary_selector_from_token(
			ivy_token_create_ident("call"));

		struct expr_parser_state *msg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);

		msg_expr->s_msg = (struct ivy_ast_msg_node *)msg;
		msg_expr->s_sub_type = EXPR_SUBTYPE_COMPLEX_MSG;
		msg_expr->s_type = EXPR_TYPE_ARITH;
		msg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

		msg_expr->s_prev_token = state->s_prev_token = IVY_SYM_LEFT_PAREN;

		return PARSE_RESULT(IVY_OK, 0);
	}

	/* this is a generic parenthesis-enclosed sub-expression.
	 * create a new sub-expr parser to handle it */

	if (state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
		/* this is an unlabeled complex message arg */
		if (state->s_prev_token != IVY_SYM_COMMA
		    && state->s_prev_token != IVY_SYM_LEFT_PAREN) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		struct ivy_token *empty_label = malloc(sizeof *empty_label);
		if (!empty_label) {
			return PARSE_RESULT(IVY_ERR_NO_MEMORY, 0);
		}
		memset(empty_label, 0x0, sizeof *empty_label);
		empty_label->t_type = IVY_TOK_LABEL;

		b_queue_push_back(&state->s_labels, &empty_label->t_entry);

		struct expr_parser_state *arg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
		expr_copy_terminators(state, arg_expr);
		expr_add_terminator(arg_expr, IVY_SYM_COMMA);
		arg_expr->s_sub_type = EXPR_SUBTYPE_COMPLEX_ARG;
		arg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

		return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
	}

	struct expr_parser_state *sub_expr
		= (struct expr_parser_state *)parser_push_state(
			ctx, IVY_AST_EXPR, 0);
	expr_copy_terminators(state, sub_expr);
	sub_expr->s_paren_depth = state->s_paren_depth + 1;
	sub_expr->s_subexpr_depth = state->s_subexpr_depth + 1;
	sub_expr->s_sub_type = EXPR_SUBTYPE_PAREN;

	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_right_paren(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (expr_terminates_at_token(state, IVY_SYM_RIGHT_PAREN)) {
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags = PARSE_REPEAT_TOKEN;
		return result;
	}

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_paren_depth == 0 && state->s_sub_type == EXPR_SUBTYPE_NONE) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_prev_token = IVY_SYM_RIGHT_PAREN;
	return expr_finalise_and_return(ctx, state);
}

struct token_parse_result arith_parse_left_brace(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type == EXPR_TYPE_NONE) {
		state->s_type = EXPR_TYPE_ARITH;
	}

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_prev_component != EXPR_CMP_OPERATOR
	    && state->s_prev_component != EXPR_CMP_NONE) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	parser_push_state(ctx, IVY_AST_PKG, 0);
	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_right_brace(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	state->s_prev_token = IVY_SYM_RIGHT_BRACE;
	struct token_parse_result result = expr_finalise_and_return(ctx, state);
	result.r_flags = PARSE_REPEAT_TOKEN;
	return result;
}

struct token_parse_result arith_parse_left_bracket(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type == EXPR_TYPE_STMT) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_prev_component == EXPR_CMP_OPERAND
	    || state->s_prev_component == EXPR_CMP_MSG) {
		/* subscript operator */

		state->s_prev_token = IVY_SYM_LEFT_BRACKET;
		struct ivy_ast_op_node *subscript
			= (struct ivy_ast_op_node *)ast_node_create(IVY_AST_OP);
		subscript->n_op = ivy_operator_get_by_id(IVY_OP_SUBSCRIPT);
		arith_push_operator(state, (struct ivy_ast_node *)subscript);

		struct expr_parser_state *index
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
		expr_add_terminator(index, IVY_SYM_RIGHT_BRACKET);
		index->s_subexpr_depth = state->s_subexpr_depth + 1;

		return PARSE_RESULT(IVY_OK, 0);
	}

	/* lambda */

	state->s_prev_token = IVY_SYM_LEFT_BRACKET;
	state->s_type = EXPR_TYPE_ARITH;

	parser_push_state(ctx, IVY_AST_LAMBDA, 0);
	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_right_bracket(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (expr_terminates_at_token(state, IVY_SYM_RIGHT_BRACKET)) {
		state->s_prev_token = IVY_SYM_RIGHT_BRACKET;
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags = PARSE_REPEAT_TOKEN;
		return result;
	}

	if (state->s_prev_token == IVY_SYM_LEFT_BRACKET) {
		/* we've just parsed a subscript operator. nothing further to do here. */
		return PARSE_RESULT(IVY_OK, 0);
	}

	state->s_prev_token = IVY_SYM_RIGHT_BRACKET;
	struct token_parse_result result = expr_finalise_and_return(ctx, state);
	result.r_flags = PARSE_REPEAT_TOKEN;
	return result;
}

static struct ivy_ast_selector_node *keyword_selector_from_label_list(b_queue *labels)
{
	struct ivy_ast_selector_node *sel
		= (struct ivy_ast_selector_node *)ast_node_create(IVY_AST_SELECTOR);

	b_queue_iterator it = {0};

	b_queue_iterator_begin(labels, &it);
	while (b_queue_iterator_is_valid(&it)) {
		struct ivy_token *label
			= b_unbox(struct ivy_token, it.entry, t_entry);
		b_queue_iterator_erase(&it);
		b_queue_push_back(&sel->n_arg_labels, &label->t_entry);
	}

	return sel;
}

static struct ivy_ast_cascade_node *expr_finalise_cascade(
	struct expr_parser_state *state)
{
	struct ivy_ast_cascade_node *cascade
		= (struct ivy_ast_cascade_node *)ast_node_create(IVY_AST_CASCADE);

	cascade->n_recipient = state->s_recipient;

	b_queue_iterator it = {0};
	b_queue_iterator_begin(&state->s_cascade_msg, &it);
	while (b_queue_iterator_is_valid(&it)) {
		struct ivy_ast_node *msg
			= b_unbox(struct ivy_ast_node, it.entry, n_entry);
		b_queue_iterator_erase(&it);
		b_queue_push_back(&cascade->n_msg, &msg->n_entry);
	}

	return cascade;
}

static struct ivy_ast_msg_node *expr_finalise_keyword_msg(
	struct expr_parser_state *state)
{
	struct ivy_ast_msg_node *msg
		= (struct ivy_ast_msg_node *)ast_node_create(IVY_AST_MSG);

	msg->n_recipient = state->s_recipient;
	msg->n_sel = keyword_selector_from_label_list(&state->s_labels);

	b_queue_iterator it = {0};

	b_queue_iterator_begin(&state->s_args, &it);
	while (b_queue_iterator_is_valid(&it)) {
		struct ivy_ast_node *arg
			= b_unbox(struct ivy_ast_node, it.entry, n_entry);
		b_queue_iterator_erase(&it);

		b_queue_push_back(&msg->n_arg, &arg->n_entry);
	}

	return msg;
}

static struct ivy_ast_msg_node *expr_finalise_complex_msg(
	struct expr_parser_state *state)
{
	struct ivy_ast_msg_node *msg = state->s_msg;
	if (!msg) {
		return NULL;
	}

	state->s_msg = NULL;

	b_queue_iterator it = {0};
	b_queue_iterator_begin(&state->s_labels, &it);
	while (b_queue_iterator_is_valid(&it)) {
		struct ivy_token *label
			= b_unbox(struct ivy_token, it.entry, t_entry);
		b_queue_iterator_erase(&it);
		b_queue_push_back(&msg->n_sel->n_arg_labels, &label->t_entry);
	}

	b_queue_iterator_begin(&state->s_args, &it);
	while (b_queue_iterator_is_valid(&it)) {
		struct ivy_ast_node *arg
			= b_unbox(struct ivy_ast_node, it.entry, n_entry);
		b_queue_iterator_erase(&it);

		b_queue_push_back(&msg->n_arg, &arg->n_entry);
	}

	return msg;
}

static enum ivy_status begin_cascade_operation(struct ivy_parser *ctx)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	/* this is the beginning of a cascade operation */

	struct ivy_ast_msg_node *first_msg = NULL;

	if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_MSG) {
		first_msg = expr_finalise_keyword_msg(state);
		parser_pop_state(ctx, 0);
	} else {
		/* we need to find who the first message in the cascade is being sent to. */
		enum ivy_operator_precedence min_precedence
			= IVY_PRECEDENCE_CASCADE;

		struct ivy_ast_node *prev = b_unbox(
			struct ivy_ast_node,
			b_queue_last(&state->s_operator_stack), n_entry);
		if (prev && prev->n_type == IVY_AST_MSG) {
			/* unary complex messages (which will be found on the
			 * operator stack) have a very high precedence (much
			 * higher than most arithmetic operators), so the
			 * recipient will be much narrower. this also means that
			 * any subsequent messages in the cascade inherit this
			 * high precedence, regardless of their type. */
			min_precedence = IVY_PRECEDENCE_UNARY_MSG;
		}

		struct ivy_ast_node *expr = NULL;
		enum ivy_status status
			= expr_finalise_arith(state, &expr, min_precedence);
		if (status != IVY_OK) {
			return status;
		}

		if (expr->n_type != IVY_AST_MSG) {
			/* the recipient and first message of the cascade
			 * operation is ambiguous due to operator precedence.
			 * this is usually resolved by adding parentheses
			 * (either around the recipient or around the cascade)
			 * to make the recipient and first message clear. */
			return IVY_ERR_BAD_SYNTAX;
		}

		first_msg = (struct ivy_ast_msg_node *)expr;
	}

	struct expr_parser_state *cascade_expr
		= (struct expr_parser_state *)parser_push_state(
			ctx, IVY_AST_EXPR, 0);

	if (!first_msg) {
		return IVY_ERR_BAD_SYNTAX;
	}

	cascade_expr->s_recipient = first_msg->n_recipient;
	first_msg->n_recipient = NULL;

	cascade_expr->s_sub_type = EXPR_SUBTYPE_CASCADE;
	cascade_expr->s_type = EXPR_TYPE_ARITH;
	cascade_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

	b_queue_push_back(&cascade_expr->s_cascade_msg, &first_msg->n_base.n_entry);

	struct expr_parser_state *msg_expr
		= (struct expr_parser_state *)parser_push_state(
			ctx, IVY_AST_EXPR, 0);
	msg_expr->s_sub_type = EXPR_SUBTYPE_MSG;
	msg_expr->s_type = EXPR_TYPE_ARITH;
	msg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

	return IVY_OK;
}

struct token_parse_result arith_parse_semicolon(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	bool end_subexpr = false;

	switch (state->s_sub_type) {
	case EXPR_SUBTYPE_KEYWORD_ARG:
	case EXPR_SUBTYPE_MSG:
		end_subexpr = true;
		break;
	case EXPR_SUBTYPE_KEYWORD_MSG:
	case EXPR_SUBTYPE_CASCADE:
	case EXPR_SUBTYPE_COMPLEX_ARG:
	case EXPR_SUBTYPE_NONE:
		break;
	default:
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		break;
	}

	if (end_subexpr) {
		/* finish parsing this expression and let the parent context handle the semicolon. */
		struct ivy_ast_node *expr = NULL;
		enum ivy_status status = expr_finalise_arith(
			state, &expr, IVY_PRECEDENCE_ASSIGN);
		if (status != IVY_OK) {
			return PARSE_RESULT(status, 0);
		}

		parser_replace_current_node(ctx, expr);
		parser_pop_state(ctx, STATE_ADD_NODE_TO_PARENT);
		return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
	}

	struct expr_parser_state *parent_state = parser_get_parent_state(
		ctx, IVY_AST_EXPR, struct expr_parser_state);

	if (state->s_sub_type == EXPR_SUBTYPE_CASCADE) {
		/* this is another message in a cascade series. */
		struct expr_parser_state *msg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);

		msg_expr->s_recipient = NULL;
		msg_expr->s_sub_type = EXPR_SUBTYPE_MSG;
		msg_expr->s_type = EXPR_TYPE_ARITH;
		msg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;

		return PARSE_RESULT(IVY_OK, 0);
	}

	if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_MSG && !state->s_recipient) {
		struct ivy_ast_msg_node *msg = expr_finalise_keyword_msg(state);
		if (!msg) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		parser_replace_current_node(ctx, (struct ivy_ast_node *)msg);
		parser_pop_state(ctx, STATE_ADD_NODE_TO_PARENT);
		return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
	}

	enum ivy_status status = begin_cascade_operation(ctx);

	return PARSE_RESULT(status, 0);
}

static struct ivy_ast_node *create_return_node(struct ivy_ast_node *val)
{
	struct ivy_ast_return_node *ret
		= (struct ivy_ast_return_node *)ast_node_create(IVY_AST_RETURN);
	if (!ret) {
		return NULL;
	}

	ret->n_val = val;
	return (struct ivy_ast_node *)ret;
}

struct token_parse_result expr_finalise(
	struct ivy_parser *ctx, struct expr_parser_state *state,
	enum ivy_operator_precedence min_precedence, struct ivy_ast_node **result)
{
	int flags = 0;
	if (state->s_subexpr_depth > 0) {
		flags = PARSE_REPEAT_TOKEN;
	}

	if (state->s_paren_depth > 0 && state->s_prev_token == IVY_SYM_RIGHT_PAREN) {
		/* this is the ending right paren in a parenthesised expression, so we need to consume it. */
		flags = 0;
	}

	if (state->s_sub_type == EXPR_SUBTYPE_MSG) {
		/* this is the end of a unary message (probably in a cascade operation). */
		struct ivy_ast_node *expr = NULL;
		enum ivy_status status = expr_finalise_arith(
			state, &expr, IVY_PRECEDENCE_CASCADE);
		if (status != IVY_OK) {
			return PARSE_RESULT(status, 0);
		}

		if (state->s_return && expr) {
			expr = create_return_node(expr);
		}

		*result = expr;
		return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
	}

	if (state->s_sub_type == EXPR_SUBTYPE_CASCADE) {
		/* this is the end of a cascade operation */
		struct ivy_ast_cascade_node *cascade
			= expr_finalise_cascade(state);

		if (state->s_return && cascade) {
			cascade = (struct ivy_ast_cascade_node *)create_return_node(
				(struct ivy_ast_node *)cascade);
		}

		*result = (struct ivy_ast_node *)cascade;
		return PARSE_RESULT(IVY_OK, flags);
	}

	if (state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
		/* this is the end of a complex message */
		struct ivy_ast_msg_node *msg = expr_finalise_complex_msg(state);

		if (state->s_return && msg) {
			msg = (struct ivy_ast_msg_node *)create_return_node(
				(struct ivy_ast_node *)msg);
		}

		*result = (struct ivy_ast_node *)msg;
		return PARSE_RESULT(IVY_OK, 0);
	}

	if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_MSG) {
		/* this is the end of a keyword-message */
		struct ivy_ast_msg_node *msg = expr_finalise_keyword_msg(state);

		if (state->s_return && msg) {
			msg = (struct ivy_ast_msg_node *)create_return_node(
				(struct ivy_ast_node *)msg);
		}

		*result = (struct ivy_ast_node *)msg;
		return PARSE_RESULT(IVY_OK, flags);
	}

	/* this is the end of a regular expression or sub-expression */
	struct ivy_ast_node *expr = NULL;
	enum ivy_status status = expr_finalise_arith(state, &expr, min_precedence);
	if (status != IVY_OK) {
		return PARSE_RESULT(status, 0);
	}

	if (expr && state->s_return) {
		expr = create_return_node(expr);
	}

	*result = expr;
	return PARSE_RESULT(IVY_OK, flags);
}

struct token_parse_result expr_finalise_and_return(
	struct ivy_parser *ctx, struct expr_parser_state *state)
{
	struct ivy_ast_node *expr_node = NULL;
	struct token_parse_result result
		= expr_finalise(ctx, state, IVY_PRECEDENCE_ASSIGN, &expr_node);

	if (result.r_status != IVY_OK) {
		return result;
	}

	parser_replace_current_node(ctx, expr_node);
	parser_pop_state(ctx, STATE_ADD_NODE_TO_PARENT);
	return result;
}

struct token_parse_result arith_parse_dot(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_paren_depth > 0) {
		/* end-of-expression with mismatched parentheses */
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (expr_terminates_at_token(state, IVY_SYM_DOT)) {
		/* treat this as a statement terminator. */
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags |= PARSE_REPEAT_TOKEN;
		return result;
	}

	state->s_prev_token = IVY_SYM_DOT;
	return expr_finalise_and_return(ctx, state);
}

struct token_parse_result arith_parse_bang(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_paren_depth > 0) {
		/* end-of-expression with mismatched parentheses */
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_prev_token = IVY_SYM_BANG;
	struct token_parse_result result = expr_finalise_and_return(ctx, state);
	result.r_flags = PARSE_REPEAT_TOKEN;
	return result;
}

struct token_parse_result arith_parse_caret(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	/* caret must be used at the beginning of a top-level expression */
	if (state->s_subexpr_depth > 0 || state->s_paren_depth > 0) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (!b_queue_empty(&state->s_operator_stack)
	    || !b_queue_empty(&state->s_output_queue)) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_prev_token = IVY_SYM_CARET;
	state->s_return = true;
	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result arith_parse_comma(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
		/* this is a comma separator between two complex message args */
		state->s_prev_token = IVY_SYM_COMMA;
		return PARSE_RESULT(IVY_OK, 0);
	}

	if (expr_terminates_at_token(state, IVY_SYM_COMMA)) {
		struct token_parse_result result
			= expr_finalise_and_return(ctx, state);
		result.r_flags = PARSE_REPEAT_TOKEN;
		return result;
	}

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_paren_depth > 0
	    && (state->s_prev_component == EXPR_CMP_OPERAND
	        || state->s_prev_component == EXPR_CMP_MSG)) {
		struct ivy_ast_node *item = NULL;
		struct token_parse_result result
			= expr_finalise(ctx, state, IVY_PRECEDENCE_ASSIGN, &item);

		if (result.r_status != IVY_OK) {
			return result;
		}

		if (!item) {
			/* empty tuple member expression. */
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		if (state->s_sub_type == EXPR_SUBTYPE_PAREN
		    && b_queue_empty(&state->s_output_queue)
		    && b_queue_empty(&state->s_operator_stack)) {
			parser_pop_state(ctx, 0);
		} else {
			/* the tuple parser will handle the parentheses for us. */
			state->s_paren_depth--;
		}

		parser_push_state(ctx, IVY_AST_TUPLE, (uintptr_t)item);
		return PARSE_RESULT(IVY_OK, 0);
	}

	state->s_prev_token = IVY_SYM_COMMA;
	return expr_finalise_and_return(ctx, state);
}

extern struct token_parse_result arith_parse_equal_right_angle(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	state->s_prev_token = IVY_SYM_EQUAL_RIGHT_ANGLE;
	struct token_parse_result result = expr_finalise_and_return(ctx, state);

	result.r_flags |= PARSE_REPEAT_TOKEN;
	return result;
}

struct token_parse_result arith_parse_label(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct expr_parser_state *state
		= parser_get_state(ctx, struct expr_parser_state);

	if (state->s_type != EXPR_TYPE_ARITH) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_ARG) {
		/* we are currently parsing a keyword or complex message
		 * argument, and have just encountered the label denoting the
		 * next argument. terminate here and propagate this label to the
		 * parent keyword-message parser context. */
		struct ivy_ast_node *expr = NULL;
		struct token_parse_result result
			= expr_finalise(ctx, state, IVY_PRECEDENCE_ASSIGN, &expr);
		if (result.r_status != IVY_OK) {
			return result;
		}

		result.r_flags |= PARSE_REPEAT_TOKEN;

		parser_replace_current_node(ctx, expr);
		parser_pop_state(ctx, STATE_ADD_NODE_TO_PARENT);
		return result;
	}

	if (state->s_sub_type != EXPR_SUBTYPE_KEYWORD_MSG
	    && state->s_sub_type != EXPR_SUBTYPE_COMPLEX_MSG) {
		/* this is the beginning of a new keyword-message */
		struct expr_parser_state *msg_expr;
		bool new_parser = true;

		if (b_queue_empty(&state->s_operator_stack)
		    && b_queue_empty(&state->s_output_queue)) {
			new_parser = false;
		}

		if (new_parser) {
			msg_expr = (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
			expr_copy_terminators(state, msg_expr);
		} else {
			msg_expr = state;
		}

		/* the only operator with a lower precedence than
		 * keyword-messages is assignment. everything in the preceding
		 * expression, up to but not including any un-parenthesised
		 * assignments, is the recipient of the message. */
		struct ivy_ast_node *expr = NULL;

		if (state->s_sub_type != EXPR_SUBTYPE_MSG) {
			enum ivy_status status = expr_finalise_arith(
				state, &expr, IVY_PRECEDENCE_KEYWORD_MSG);
			if (status != IVY_OK) {
				return PARSE_RESULT(status, 0);
			}
		}

		msg_expr->s_recipient = expr;
		msg_expr->s_sub_type = EXPR_SUBTYPE_KEYWORD_MSG;
		msg_expr->s_type = EXPR_TYPE_ARITH;
		msg_expr->s_subexpr_depth = state->s_subexpr_depth;

		if (new_parser) {
			msg_expr->s_subexpr_depth++;
		}

		state = msg_expr;
	}

	if (state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
		/* this label denotes the start of a complex message arg */
		if (state->s_prev_token != IVY_SYM_COMMA
		    && state->s_prev_token != IVY_SYM_LEFT_PAREN) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		b_queue_push_back(&state->s_labels, &tok->t_entry);

		struct expr_parser_state *arg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
		expr_copy_terminators(state, arg_expr);
		expr_add_terminator(arg_expr, IVY_SYM_COMMA);
		arg_expr->s_sub_type = EXPR_SUBTYPE_COMPLEX_ARG;
		arg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;
	} else if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_MSG) {
		/* we may have just finished parsing a keyword-message argument,
		 * and this label marks the start of a new one. store the label
		 * and create a new argument parsing context. */
		b_queue_push_back(&state->s_labels, &tok->t_entry);

		struct expr_parser_state *arg_expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
		expr_copy_terminators(state, arg_expr);
		expr_add_terminator(arg_expr, IVY_TOK_LABEL);
		arg_expr->s_sub_type = EXPR_SUBTYPE_KEYWORD_ARG;
		arg_expr->s_subexpr_depth = state->s_subexpr_depth + 1;
	}

	return PARSE_RESULT(IVY_OK, 0);
}

enum ivy_status arith_add_child(
	struct parser_state *parent, struct ivy_ast_node *child)
{
	struct expr_parser_state *state = (struct expr_parser_state *)parent;

	if (state->s_sub_type == EXPR_SUBTYPE_CASCADE) {
		/* treat the child node as a cascaded message */
		b_queue_push_back(&state->s_cascade_msg, &child->n_entry);
	} else if (
		state->s_sub_type == EXPR_SUBTYPE_KEYWORD_MSG
		|| state->s_sub_type == EXPR_SUBTYPE_COMPLEX_MSG) {
		/* treat the child node as a keyword-message argument */
		b_queue_push_back(&state->s_args, &child->n_entry);
	} else if (state->s_sub_type == EXPR_SUBTYPE_KEYWORD_ARG) {
		/* treat the child node as a sub-expression enclosed in
		 * parentheses (i.e. an operand). */
		b_queue_push_back(&state->s_output_queue, &child->n_entry);
		state->s_prev_component = EXPR_CMP_OPERAND;
	} else if (child->n_type == IVY_AST_MSG) {
		arith_push_operator(state, child);
		state->s_prev_component = EXPR_CMP_MSG;
	} else {
		/* treat the child node as a sub-expression enclosed in
		 * parentheses (i.e. an operand). */
		b_queue_push_back(&state->s_output_queue, &child->n_entry);
		state->s_prev_component = EXPR_CMP_OPERAND;
	}

	return IVY_OK;
}