If y is less than x , evaluation succeeds and produces the value x . Otherwise, evaluation fails, and no value is produced. Comparison operators produce the value of their right operand if they succeed. Failure drives control expressions and inhibits subsequent evaluation. The backtracking implied by the goal-directed evaluation mechanism is limited to the expression in which it occurs.
Icon has numerous built-in procedures and operators that help analyze strings.
Many of these take strings and positions as operands and return strings or positions. Positions denote locations between characters. Strings can be analyzed by manipulating positions explicitly, but Icon's string scanning facility eliminates the need for most explicit positions. The expression e typically includes string analysis operations, but may include any operation. If the advancement is successful, move returns the i -character substring between the initial and final positions.