Meaning of FILTER in English

FILTER

1. (Originally Unix , now also MS-DOS ) A program that processes an input data stream into an output data stream in some well-defined way, and does no I/O to anywhere else except possibly on error conditions; one designed to be used as a stage in a pipeline (see plumbing ). Compare sponge .

2. ( functional programming ) A higher-order function which takes a predicate and a list and returns those elements of the list for which the predicate is true. In Haskell :

filter p [] = [] filter p (x:xs) = if p x then x : rest else rest where rest = filter p xs

See also filter promotion .

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