bshell/bshell.runtime/parse/syntax/arith.c

#include "../syntax.h"

#include <bshell/runtime/operator.h>
#include <fx/queue.h>

enum expr_component {
	EXPR_C_NONE = 0,
	EXPR_C_OPERAND,
	EXPR_C_BINARY_OP,
	EXPR_C_UNARY_OP,
};

struct expr_bshell_parse_ctx {
	fx_queue expr_bshell_operator_stack, expr_out_queue;
	enum expr_component expr_prev;
	unsigned int expr_prev_symbol;
	enum bshell_operator_precedence expr_minimum_precedence;
	bool expr_done, expr_fail;
};

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

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

static bool finalise_expr(
	struct expr_bshell_parse_ctx *ctx,
	struct bshell_ast_node **out,
	enum bshell_operator_precedence minimum_precedence)
{
	fx_queue_entry *entry = NULL;
	while (true) {
		entry = fx_queue_pop_back(&ctx->expr_bshell_operator_stack);
		if (!entry) {
			break;
		}

		struct bshell_op_ast_node *node = fx_unbox(
			struct bshell_op_ast_node,
			entry,
			n_base.n_entry);
		if (!node) {
			/* this should never happen */
			return false;
		}

		const struct bshell_operator_info *op = node->n_op;

		/* 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) {
			fx_queue_push_back(
				&ctx->expr_bshell_operator_stack,
				entry);
			break;
		}

		fx_queue_push_back(&ctx->expr_out_queue, entry);
	}

	fx_queue q = FX_QUEUE_INIT;
	fx_queue_entry *tmp = NULL;
	entry = fx_queue_first(&ctx->expr_out_queue);
	int i = 0;

	while (entry) {
		struct bshell_ast_node *item
			= fx_unbox(struct bshell_ast_node, entry, n_entry);
		fx_queue_entry *next = fx_queue_next(entry);
		fx_queue_delete(&ctx->expr_out_queue, entry);

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

		const struct bshell_operator_info *op = NULL;

		struct bshell_op_ast_node *op_node
			= (struct bshell_op_ast_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)) {
			fx_queue_push_back(&q, &item->n_entry);
			goto next;
		}

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

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

#if 0
			bshell_ast_node_extend_bounds_recursive(
				(struct ivy_bshell_ast_node *)op_node,
				(struct ivy_bshell_ast_node *)tmp);
#endif
		}

		if (op->op_arity == BSHELL_OPA_BINARY) {
			tmp = fx_queue_pop_back(&q);
			op_node->n_left = fx_unbox(
				struct bshell_ast_node,
				tmp,
				n_entry);

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

#if 0
				bshell_ast_node_extend_bounds_recursive(
					(struct ivy_bshell_ast_node *)op_node,
					(struct ivy_bshell_ast_node *)tmp);
#endif
			}
		}

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

#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. */
	entry = fx_queue_first(&ctx->expr_bshell_operator_stack);
	while (entry) {
		fx_queue_entry *entry2 = fx_queue_pop_front(&q);
		if (!entry2) {
			return false;
		}

		fx_queue_push_back(&ctx->expr_out_queue, entry2);
		entry = fx_queue_next(entry);
	}

#if 0
	debug_printf("** after de-linearisation:\n");
	print_expr_queues(state);
	ivy_bshell_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 = fx_queue_pop_back(&q);
	*out = fx_unbox(struct bshell_ast_node, tmp, n_entry);

	return true;
}

bool peek_arith_expr(struct bshell_parse_ctx *ctx)
{
	switch (peek_token_type(ctx)) {
	case BSHELL_TOK_SYMBOL:
		return bshell_operator_get_by_token(peek_unknown_symbol(ctx));
	case BSHELL_TOK_INT:
	case BSHELL_TOK_DOUBLE:
	case BSHELL_TOK_STRING:
	case BSHELL_TOK_VAR:
	case BSHELL_TOK_STR_START:
	case BSHELL_TOK_OPERATOR:
		return true;
	default:
		return false;
	}
}

static bool parse_subexpr(struct bshell_parse_ctx *ctx, struct bshell_ast_node **out)
{
	if (!parse_symbol(ctx, BSHELL_SYM_LEFT_PAREN)) {
		report_error(ctx, "expected `(`");
	}

	struct bshell_ast_node *v = NULL;
	if (!parse_expr(ctx, &v)) {
		report_error(ctx, "error while parsing parenthesis expression");
		return false;
	}

	if (!parse_symbol(ctx, BSHELL_SYM_RIGHT_PAREN)) {
		report_error(ctx, "expected `)` after parenthesis expression");
		return false;
	}

	*out = v;
	return true;
}

static bool parse_stmt_block(
	struct bshell_parse_ctx *ctx,
	struct bshell_ast_node **out)
{
	if (!parse_symbol(ctx, BSHELL_SYM_DOLLAR_LEFT_PAREN)) {
		report_error(ctx, "expected `$(`");
		return false;
	}

	if (parse_symbol(ctx, BSHELL_SYM_RIGHT_PAREN)) {
		*out = bshell_ast_node_create(BSHELL_AST_NULL);
		return true;
	}

	struct bshell_ast_node *v = NULL;
	if (!parse_statement_list(ctx, &v)) {
		return false;
	}

	if (!parse_symbol(ctx, BSHELL_SYM_RIGHT_PAREN)) {
		report_error(ctx, "expected ')' after subexpression");
		bshell_ast_node_destroy(v);
		return false;
	}

	*out = v;
	return true;
}

static bool parse_hashtable(struct bshell_parse_ctx *ctx, struct bshell_ast_node **out)
{
	if (!parse_symbol(ctx, BSHELL_SYM_AT_LEFT_BRACE)) {
		report_error(ctx, "expected `@{`");
		return false;
	}

	parse_linefeed(ctx);

	struct bshell_hashtable_ast_node *table
		= (struct bshell_hashtable_ast_node *)bshell_ast_node_create(
			BSHELL_AST_HASHTABLE);
	if (!table) {
		ctx->p_status = BSHELL_ERR_NO_MEMORY;
		return false;
	}

	size_t nr_items = 0;
	bool ok = true;
	while (ok) {
		if (parse_symbol(ctx, BSHELL_SYM_RIGHT_BRACE)) {
			break;
		}

		parse_linefeed(ctx);

		struct bshell_hashtable_item_ast_node *item
			= (struct bshell_hashtable_item_ast_node *)
				bshell_ast_node_create(
					BSHELL_AST_HASHTABLE_ITEM);
		struct bshell_lex_token *tok = NULL;
		if (parse_word(ctx, &tok)) {
			struct bshell_string_ast_node *v
				= (struct bshell_string_ast_node *)
					bshell_ast_node_create(
						BSHELL_AST_STRING);
			v->n_value = tok;
			item->n_key = (struct bshell_ast_node *)v;
		} else if (!parse_arith_value(ctx, &item->n_key)) {
			report_error(ctx, "failed to parse hashtable key");
			bshell_ast_node_destroy((struct bshell_ast_node *)item);
			ok = false;
			break;
		}

		if (!parse_symbol(ctx, BSHELL_SYM_EQUAL)) {
			report_error(ctx, "expected `=` after hashtable key");
			bshell_ast_node_destroy((struct bshell_ast_node *)item);
			ok = false;
			break;
		}

		if (!parse_expr(ctx, &item->n_value)) {
			report_error(ctx, "failed to parse hashtable value");
			bshell_ast_node_destroy((struct bshell_ast_node *)item);
			ok = false;
			break;
		}

		fx_queue_push_back(&table->n_items, &item->n_base.n_entry);
		nr_items++;

		if (parse_symbol(ctx, BSHELL_SYM_RIGHT_BRACE)) {
			break;
		}

		if (!parse_linefeed(ctx)
		    && !parse_symbol(ctx, BSHELL_SYM_SEMICOLON)) {
			report_error(
				ctx,
				"expected `;`, `}`, or linefeed after "
				"hashtable value");
			ok = false;
			break;
		}
	}

	if (!ok) {
		bshell_ast_node_destroy((struct bshell_ast_node *)table);
		return false;
	}

	*out = (struct bshell_ast_node *)table;
	return true;
}

static bool parse_array(struct bshell_parse_ctx *ctx, struct bshell_ast_node **out)
{
	if (!parse_symbol(ctx, BSHELL_SYM_AT_LEFT_PAREN)) {
		report_error(ctx, "expected `@(`");
		return false;
	}

	struct bshell_array_ast_node *array
		= (struct bshell_array_ast_node *)bshell_ast_node_create(
			BSHELL_AST_ARRAY);
	if (!array) {
		ctx->p_status = BSHELL_ERR_NO_MEMORY;
		return false;
	}

	size_t nr_items = 0;
	bool ok = true;
	while (ok) {
		if (parse_symbol(ctx, BSHELL_SYM_RIGHT_PAREN)) {
			break;
		}

		if (nr_items && !parse_symbol(ctx, BSHELL_SYM_COMMA)) {
			report_error(
				ctx,
				"expected `,` or `)` after array value");
			ok = false;
		}

		struct bshell_ast_node *item = NULL;
		if (!parse_arith_value(ctx, &item)) {
			report_error(ctx, "failed to parse array item");
			ok = false;
			break;
		}

		fx_queue_push_back(&array->n_items, &item->n_entry);
		nr_items++;
	}

	if (!ok) {
		bshell_ast_node_destroy((struct bshell_ast_node *)array);
		return false;
	}

	*out = (struct bshell_ast_node *)array;
	return true;
}

bool parse_fstring(struct bshell_parse_ctx *ctx, struct bshell_ast_node **out)
{
	if (peek_token_type(ctx) != BSHELL_TOK_STR_START) {
		return false;
	}

	discard_token(ctx);

	struct bshell_fstring_ast_node *fstring
		= (struct bshell_fstring_ast_node *)bshell_ast_node_create(
			BSHELL_AST_FSTRING);
	if (!fstring) {
		ctx->p_status = BSHELL_ERR_NO_MEMORY;
		return false;
	}

	bool ok = true;
	while (ok) {
		if (peek_token_type(ctx) == BSHELL_TOK_STR_END) {
			discard_token(ctx);
			break;
		}

		struct bshell_ast_node *item = NULL;
		if (!parse_arith_value(ctx, &item)) {
			ok = false;
			break;
		}

		fx_queue_push_back(&fstring->n_elements, &item->n_entry);
	}

	if (!ok) {
		bshell_ast_node_destroy((struct bshell_ast_node *)fstring);
		fstring = NULL;
	}

	*out = (struct bshell_ast_node *)fstring;
	return ok;
}

bool parse_arith_value(struct bshell_parse_ctx *ctx, struct bshell_ast_node **out)
{
	struct bshell_lex_token *tok = peek_token(ctx);
	switch (tok->tok_type) {
	case BSHELL_TOK_INT: {
		struct bshell_int_ast_node *v
			= (struct bshell_int_ast_node *)bshell_ast_node_create(
				BSHELL_AST_INT);
		v->n_value = claim_token(ctx);
		*out = (struct bshell_ast_node *)v;
		return true;
	}
	case BSHELL_TOK_DOUBLE: {
		struct bshell_double_ast_node *v
			= (struct bshell_double_ast_node *)
				bshell_ast_node_create(BSHELL_AST_DOUBLE);
		v->n_value = claim_token(ctx);
		*out = (struct bshell_ast_node *)v;
		return true;
	}
	case BSHELL_TOK_STRING: {
		struct bshell_string_ast_node *v
			= (struct bshell_string_ast_node *)
				bshell_ast_node_create(BSHELL_AST_STRING);
		v->n_value = claim_token(ctx);
		*out = (struct bshell_ast_node *)v;
		return true;
	}
	case BSHELL_TOK_WORD: {
		struct bshell_word_ast_node *v
			= (struct bshell_word_ast_node *)bshell_ast_node_create(
				BSHELL_AST_WORD);
		v->n_value = claim_token(ctx);
		*out = (struct bshell_ast_node *)v;
		return true;
	}
	case BSHELL_TOK_VAR: {
		struct bshell_var_ast_node *v
			= (struct bshell_var_ast_node *)bshell_ast_node_create(
				BSHELL_AST_VAR);
		v->n_ident = claim_token(ctx);
		*out = (struct bshell_ast_node *)v;
		return true;
	}
	case BSHELL_TOK_STR_START:
		return parse_fstring(ctx, out);
	case BSHELL_TOK_SYMBOL:
		switch (tok->tok_symbol) {
		case BSHELL_SYM_LEFT_PAREN:
			return parse_subexpr(ctx, out);
		case BSHELL_SYM_DOLLAR_LEFT_PAREN:
			return parse_stmt_block(ctx, out);
		case BSHELL_SYM_AT_LEFT_BRACE:
			return parse_hashtable(ctx, out);
		case BSHELL_SYM_AT_LEFT_PAREN:
			return parse_array(ctx, out);
		case BSHELL_SYM_LEFT_BRACE:
			return parse_block(ctx, out);
		default:
			report_error(ctx, "token is not a valid operand");
			return false;
		}
		break;
	default:
		report_error(ctx, "token is not a valid operand");
		return false;
	}
}

static bool parse_operand(struct bshell_parse_ctx *ctx, struct expr_bshell_parse_ctx *expr)
{
	if (expr->expr_prev == EXPR_C_OPERAND) {
		report_error(ctx, "encountered two operands in a row");
		return false;
	}

	expr->expr_prev = EXPR_C_OPERAND;

	struct bshell_ast_node *v = NULL;
	if (!parse_arith_value(ctx, &v)) {
		return false;
	}

	fx_queue_push_back(&expr->expr_out_queue, &v->n_entry);
	return true;
}

void arith_push_operator(
	struct expr_bshell_parse_ctx *state,
	struct bshell_op_ast_node *node)
{
	const struct bshell_operator_info *op = node->n_op;
	if (!op) {
		return;
	}

	while (true) {
		fx_queue_entry *top
			= fx_queue_last(&state->expr_bshell_operator_stack);
		if (!top) {
			break;
		}

		struct bshell_ast_node *top_node
			= fx_unbox(struct bshell_ast_node, top, n_entry);
		const struct bshell_operator_info *top_op = NULL;

		switch (top_node->n_type) {
		case BSHELL_AST_OP: {
			struct bshell_op_ast_node *op_node
				= (struct bshell_op_ast_node *)top_node;
			top_op = op_node->n_op;
			break;
		}
		default:
			return;
		}

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

		fx_queue_delete(&state->expr_bshell_operator_stack, top);
		fx_queue_push_back(&state->expr_out_queue, top);
	}

	fx_queue_push_back(
		&state->expr_bshell_operator_stack,
		&node->n_base.n_entry);
}

static bool parse_unary_operator(
	struct bshell_parse_ctx *ctx,
	struct expr_bshell_parse_ctx *expr)
{
	struct bshell_lex_token *tok = peek_token(ctx);

	const struct bshell_operator_info *op = NULL;
	switch (tok->tok_type) {
	case BSHELL_TOK_SYMBOL:
		op = bshell_operator_get_by_token(tok->tok_symbol);
		break;
	case BSHELL_TOK_OPERATOR:
		switch (tok->tok_operator) {
		case BSHELL_TKOP_SPLIT:
			op = bshell_operator_get_by_id(BSHELL_OP_USPLIT);
			break;
		case BSHELL_TKOP_JOIN:
			op = bshell_operator_get_by_id(BSHELL_OP_USPLIT);
			break;
		default:
			op = bshell_operator_get_by_token(tok->tok_operator);
			break;
		}
		break;
	default:
		break;
	}

	if (expr->expr_prev == EXPR_C_OPERAND
	    && op->op_location == BSHELL_OPL_PREFIX) {
		report_error(
			ctx,
			"unexpected operand before unary "
			"operator");
		return false;
	}

	if (!op) {
		report_error(ctx, "unknown unary operator");
		return false;
	}

	if (op->op_precedence < expr->expr_minimum_precedence) {
		expr->expr_done = true;
		return true;
	}

	expr->expr_prev = EXPR_C_BINARY_OP;

	struct bshell_op_ast_node *op_node
		= (struct bshell_op_ast_node *)bshell_ast_node_create(
			BSHELL_AST_OP);
	if (!op_node) {
		return false;
	}

	op_node->n_op = op;
	discard_token(ctx);
	arith_push_operator(expr, op_node);
	return true;
}

static bool parse_binary_operator(
	struct bshell_parse_ctx *ctx,
	struct expr_bshell_parse_ctx *expr)
{
	struct bshell_lex_token *tok = peek_token(ctx);

	const struct bshell_operator_info *op = NULL;
	switch (tok->tok_type) {
	case BSHELL_TOK_SYMBOL:
		op = bshell_operator_get_by_token(tok->tok_symbol);
		break;
	case BSHELL_TOK_OPERATOR:
		switch (tok->tok_operator) {
		case BSHELL_TKOP_SPLIT:
			op = bshell_operator_get_by_id(BSHELL_OP_BSPLIT);
			break;
		case BSHELL_TKOP_JOIN:
			op = bshell_operator_get_by_id(BSHELL_OP_BJOIN);
			break;
		default:
			op = bshell_operator_get_by_token(tok->tok_operator);
			break;
		}
	default:
		break;
	}

	if (!op) {
		report_error(ctx, "unknown binary operator");
		return false;
	}

	if (op->op_precedence < expr->expr_minimum_precedence) {
		expr->expr_done = true;
		return true;
	}

	if (expr->expr_prev != EXPR_C_OPERAND) {
		switch (op->op_id) {
		case BSHELL_OP_PAREN:
			break;
		default:
			report_error(
				ctx,
				"expected operand before binary "
				"operator");
			return false;
		}
	}

	expr->expr_prev = EXPR_C_BINARY_OP;

	struct bshell_op_ast_node *op_node
		= (struct bshell_op_ast_node *)bshell_ast_node_create(
			BSHELL_AST_OP);
	if (!op_node) {
		return false;
	}

	op_node->n_op = op;
	discard_token(ctx);
	arith_push_operator(expr, op_node);
	return true;
}

static bool parse_call(struct bshell_parse_ctx *ctx, struct expr_bshell_parse_ctx *expr)
{
	return false;
}

static bool parse_comma(struct bshell_parse_ctx *ctx, struct expr_bshell_parse_ctx *expr)
{
	if (BSHELL_PRECEDENCE_ARRAY < expr->expr_minimum_precedence) {
		expr->expr_done = true;
		return true;
	}

	struct bshell_ast_node *item = NULL;
	if (!finalise_expr(expr, &item, BSHELL_PRECEDENCE_ARRAY)) {
		report_error(ctx, "failed to collect first array item.");
		return false;
	}

	struct bshell_array_ast_node *array
		= (struct bshell_array_ast_node *)bshell_ast_node_create(
			BSHELL_AST_ARRAY);
	if (!array) {
		ctx->p_status = BSHELL_ERR_NO_MEMORY;
		bshell_ast_node_destroy(item);
		return false;
	}

	if (item) {
		fx_queue_push_back(&array->n_items, &item->n_entry);
	}

	while (1) {
		if (!parse_symbol(ctx, BSHELL_SYM_COMMA)) {
			break;
		}

		if (!parse_arith_expr(
			    ctx,
			    BSHELL_PRECEDENCE_ARRAY + 1,
			    &item)) {
			report_error(ctx, "failed to parse array item.");
			bshell_ast_node_destroy(
				(struct bshell_ast_node *)array);
			return false;
		}

		fx_queue_push_back(&array->n_items, &item->n_entry);
	}

	fx_queue_push_back(&expr->expr_out_queue, &array->n_base.n_entry);
	expr->expr_prev = EXPR_C_OPERAND;

	return true;
}

static bool can_use_command(struct expr_bshell_parse_ctx *ctx)
{
	switch (ctx->expr_prev_symbol) {
	case BSHELL_TOK_NONE:
	case BSHELL_SYM_EQUAL:
	case BSHELL_SYM_PLUS_EQUAL:
	case BSHELL_SYM_HYPHEN_EQUAL:
	case BSHELL_SYM_ASTERISK_EQUAL:
	case BSHELL_SYM_FORWARD_SLASH_EQUAL:
	case BSHELL_SYM_PERCENT_EQUAL:
		return true;
	default:
		return false;
	}
}

bool parse_arith_expr(
	struct bshell_parse_ctx *ctx,
	enum bshell_operator_precedence minimum_precedence,
	struct bshell_ast_node **out)
{
	struct expr_bshell_parse_ctx expr = {
		.expr_minimum_precedence = minimum_precedence,
	};

	while (!expr.expr_fail && !expr.expr_done) {
		struct bshell_lex_token *tok = peek_token(ctx);
		if (!tok) {
			break;
		}

		switch (tok->tok_type) {
		case BSHELL_TOK_LINEFEED:
			expr.expr_prev_symbol = tok->tok_type;
			expr.expr_done = true;
			break;
		case BSHELL_TOK_WORD: {
			if (!can_use_command(&expr)) {
				expr.expr_fail = !parse_operand(ctx, &expr);
				break;
			}

			expr.expr_prev_symbol = tok->tok_type;
			struct bshell_ast_node *value = NULL;
			if (!parse_command(ctx, &value)) {
				expr.expr_fail = true;
				break;
			}

			fx_queue_push_back(
				&expr.expr_out_queue,
				&value->n_entry);
			break;
		}

		case BSHELL_TOK_VAR:
		case BSHELL_TOK_INT:
		case BSHELL_TOK_DOUBLE:
		case BSHELL_TOK_STRING:
		case BSHELL_TOK_STR_START:
			expr.expr_prev_symbol = tok->tok_type;
			expr.expr_fail = !parse_operand(ctx, &expr);
			expr.expr_prev_symbol = tok->tok_type;
			break;
		case BSHELL_TOK_OPERATOR:
			expr.expr_prev_symbol = tok->tok_operator;
			switch (tok->tok_operator) {
			/* these two are special cases, as they are both
			 * unary AND binary operators */
			case BSHELL_TKOP_SPLIT:
			case BSHELL_TKOP_JOIN:
				if (expr.expr_prev == EXPR_C_OPERAND) {
					expr.expr_fail = !parse_binary_operator(
						ctx,
						&expr);
				} else {
					expr.expr_fail = !parse_unary_operator(
						ctx,
						&expr);
				}

				break;
			case BSHELL_TKOP_BNOT:
			case BSHELL_TKOP_NOT:
				expr.expr_fail
					= !parse_unary_operator(ctx, &expr);
				break;
			default:
				expr.expr_fail
					= !parse_binary_operator(ctx, &expr);
				break;
			}
			expr.expr_prev_symbol = tok->tok_operator;
			break;
		case BSHELL_TOK_SYMBOL:
			expr.expr_prev_symbol = tok->tok_symbol;

			switch (tok->tok_symbol) {
			case BSHELL_SYM_SEMICOLON:
			case BSHELL_SYM_AMPERSAND:
			case BSHELL_SYM_PIPE:
			case BSHELL_SYM_RIGHT_PAREN:
			case BSHELL_SYM_RIGHT_BRACE:
			case BSHELL_SYM_RIGHT_BRACKET:
				expr.expr_done = true;
				break;
			case BSHELL_SYM_COMMA:
				expr.expr_fail = !parse_comma(ctx, &expr);
				break;
			case BSHELL_SYM_LEFT_PAREN: {
				if (expr.expr_prev == EXPR_C_OPERAND) {
					return parse_call(ctx, &expr);
				}

				struct bshell_ast_node *v = NULL;
				expr.expr_fail = !parse_subexpr(ctx, &v);
				if (expr.expr_fail) {
					break;
				}

				fx_queue_push_back(
					&expr.expr_out_queue,
					&v->n_entry);
				expr.expr_prev = EXPR_C_OPERAND;
				break;
			}
			case BSHELL_SYM_DOLLAR_LEFT_PAREN:
			case BSHELL_SYM_AT_LEFT_PAREN:
			case BSHELL_SYM_AT_LEFT_BRACE:
			case BSHELL_SYM_LEFT_BRACE:
				expr.expr_fail = !parse_operand(ctx, &expr);
				break;
			default: {
				const struct bshell_operator_info *op
					= bshell_operator_get_by_token(
						tok->tok_symbol);
				if (op->op_arity == BSHELL_OPA_BINARY) {
					expr.expr_fail = !parse_binary_operator(
						ctx,
						&expr);
				} else {
					expr.expr_fail = !parse_unary_operator(
						ctx,
						&expr);
				}
				break;
			}
			}

			break;
		default:
			report_error(
				ctx,
				"unexpected token in arithmetic "
				"expression");
			expr.expr_fail = true;
			break;
		}
	}

	if (expr.expr_fail) {
		/* TODO cleanup */
		return false;
	}

	struct bshell_ast_node *value = NULL;
	if (!finalise_expr(&expr, &value, BSHELL_PRECEDENCE_ASSIGN)) {
		report_error(ctx, "failed to convert expression to AST");
		/* TODO cleanup */
		return false;
	}

	if (BSHELL_PRECEDENCE_PIPELINE >= expr.expr_minimum_precedence) {
		if (peek_symbol(ctx, BSHELL_SYM_PIPE)) {
			return parse_pipeline(ctx, value, out);
		}
	}

	*out = value;
	return true;
}