The int filter takes a single argument, a string filter. If the string represented by that filter consists of a nonempty sequence of digits, optionally preceded by a minus sign, then the value of the filter is the integer represented by string. Otherwise, the int filter fails to match.
    int "32"  32
    int "-2"  -2
    int "xy" // fails to match

The int filter has lower precedence than +:

    int "32" + "1"  321 // string concatenation, same as
    int ("32" + "1") 
    int "32" + 1  33 //arithemic addition, same as
    (int "32") + 1


The int filter is mainly used with regular expressions to convert sequences of digits to integers. For example, suppose some comments contains strings like "Eval: 24" in them. We can convert these to integers:

  Eval = {comment ~~ "Eval: (\d+)"
          int \1}