sieve

A Sieve is a data type with properties analogous to a physical Sieve and it is useful for building up lists of data wherein a specific constraint must be met that cannot be achieved using normal type semantics. A Sieve encapsulates a list that can only hold a certain type, specified by a identity function and is preferable to creating or building up lists by using conditional blocks or by the progressive use of filter. This is especially advantageous if a list is to be passed around and used as an accumulator. In such a configuration, the original declaring type is passed around with the Sieve so that it can be used transparently in subsequent areas of the program.