Description:
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It would be nice, if you can use some mathematical sets in if conditions. This would help to filter input values like integers, string and floats.
For example if you'll check if an input value within your range:
Normal representation -> if ($input >= 0 && $input <= 2)
Math. Set representation -> if ($input === [0; 2])

You can use braces (but they are used in PHP) to represent sets of string or numbers like -> colors === {'red', 'blue', 'yellow'}

There is also an international standard (ISO 31-11) that defines sets (http://en.wikipedia.org/wiki/ISO_31-11#Sets)