filter1. (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 xsSee also filter promotion. [Jargon File]
film at 11 ♦ FILO ♦ Filtabyte ♦ filter ♦ filter promotion ♦ FIMS ♦ Finagle's Law
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