Commonly Used List Processing Functions in FP

July 26, 2012

A list of commonly used functions for processing collections in FP languages or when adopting an FP style. Grouped by language in alphabetical order. The listing order for the functions is the same for every language. Some functions, though, are missing in some languages or there are alternative ways to accomplish the same goal.

• Clojure
• Erlang
• Haskell
• JavaScript
• Scala

Clojure

• first
• rest
• map
• filter or its dual remove
• every? or its dual not-every?
• some or its dual not-any?
• zipmap
• zip-with. There's no such function in Clojure, but the same thing can be achieved by passing at least two collections to map.
• take
• take-while
• drop
• drop-while
• reduce

Please note that some of the functions above will probably be superseded by the new reducers library.

Erlang

• hd/1
• tl/1
• lists:map/2
• lists:filter/2
• lists:all/2
• lists:any/2
• lists:zip2/2 and lists:zip3/3
• lists:takewhile/2
• lists:dropwhile/2
• lists:foldl/3
• lists:foldr/3

Haskell

• head
• tail
• map
• filter
• all or the closely related and
• any or the closely related or
• zip or any of the zip3 up to zip7 in the Data.List module
• zipWith or any of the zipWith3 up to zipWith7 in the Data.List module
• take
• drop
• takeWhile
• dropWhile
• foldl
• foldr

JavaScript (using underscore.js)

• first
• rest
• map
• filter and its dual reject
• all
• any
• zip
• reduce / inject / foldl
• reduceRight / foldr

Scala

• head
• tail
• map
• filter and its dual filterNot
• forall
• exists
• zip
• zipWith. There's no such method in Scala, instead use the zipped method which is only available for Tuple2 and Tuple3
• take
• drop
• takeWhile
• dropWhile
• foldLeft
• reduceLeft
• foldRight