User:Ushkin N/Comparison of programming languages/Functional/Fold

See Fold (higher-order function).

Language	Left fold	Right fold	Left fold without initial value	Right fold without initial value	Unfold	Notes
APL	function⍨/⌽initval,vector	function/vector,initval	function⍨/⌽vector	function/vector
C# 3.0	ienum.Aggregate(initval, func)	ienum.Reverse().Aggregate(initval, func)	ienum.Aggregate(func)	ienum.Reverse().Aggregate(func)		Aggregate is an extension method ienum is an IEnumerable<T> Similarly in all .NET languages
C++	std::accumulate(begin, end, initval, func)	std::accumulate(rbegin, rend, initval, func)				in header <numeric> begin, end, rbegin, rend are iterators func can be a function pointer or a function object
CFML	obj.reduce(func,initial)		obj.reduce(func)			Where func receives as arguments the result of the previous operation (or the initial value on the first iteration); the current item; the current item's index or key; and a reference to the obj
Clojure	(reduce func initval list)	(reduce func initval (reverse list'))	(reduce func list)	(reduce func" (reverse list))		See also clojure.core.reducers/fold
Common Lisp	(reduce func list :initial-value initval)	(reduce func list :from-end t :initial-value initval)	(reduce func list)	(reduce func list :from-end t)
Curl	{{TreeNode.default treeNode ...} .to-Iterator}	{{TreeNode.default treeNode ...} .reverse}.to-Iterator}	{for {treeNode.to-Iterator} do}	{for {{treeNode.reverse}.to-Iterator} do}		also DefaultListModel and HashTable implement to-Iterator
D	reduce!func(initval, list)	reduce!func(initval, list.reverse)	reduce!func(list)	reduce!func(list.reverse)		in module std.algorithm
Elm	List.foldl(Fun, Accumulator, List)	List.foldr(Fun, Accumulator, List)				See also List API [1]
Erlang	lists:foldl(Fun, Accumulator, List)	lists:foldr(Fun, Accumulator, List)
F#	Seq/List.fold func initval list	List.foldBack func list initval	Seq/List.reduce func list	List.reduceBack func list	Seq.unfold func initval
Gosu	Iterable.fold(f(agg, e))Iterable.reduce(init, f(agg, e)) Iterable.partition(f(e))					All are extension methods on Java's Iterable interface, arrays are also supported
Groovy	list.inject(initval, func)	list.reverse().inject(initval, func)	list.inject(func)	list.reverse().inject(func)
Haskell	foldl func initval list	foldr func initval list	foldl1 func list	foldr1 func list	unfoldr func initval
Haxe	Lambda.fold(iterable, func, initval)
J	verb~/|. initval,array	verb/ array,initval	verb~/|. array	verb/ array		u/y applies the dyad u between the items of y. "J Dictionary: Insert"
Java 8+	stream.reduce(initval, func)		stream.reduce(func)
JavaScript 1.8 ECMAScript 5	array.reduce(func, initval)	array.reduceRight(func, initval)	array.reduce(func)	array.reduceRight(func)
LFE	(lists:foldl func accum list)	(lists:foldr func accum list)
Logtalk	fold_left(Closure, Initial, List, Result)	fold_right(Closure, Initial, List, Result)				Meta-predicates provided by the meta standard library object. The abbreviations foldl and foldr may also be used.
Maple	foldl(func, initval, sequence)	foldr(func, initval, sequence)
Mathematica	Fold[func, initval, list]	Fold[func, initval, Reverse[list]]	Fold[func, list]	Fold[func, Reverse[list]]	NestWhileList[func,, initval, predicate]	Fold without an initial value is supported in versions 10.0 and higher.
Maxima	lreduce(func, list, initval)	rreduce(func, list, initval)	lreduce(func, list)	rreduce(func, list)
Mythryl	fold_left func initval list vector::fold_left func initval vector	fold_right func initval list vector::fold_right func initval vector				The supplied function takes its arguments in a tuple.
OCaml	List.fold_left func initval list Array.fold_left func initval array	List.fold_right func list initval Array.fold_right func array initval
Oz	{FoldL List Func InitVal}	{FoldR List Func InitVal}
Perl	reduce block initval, list		reduce block list			in List::Util module
PHP	array_reduce(array, func, initval)	array_reduce(array_reverse(array), func, initval)	array_reduce(array, func)	array_reduce(array_reverse(array), func)		When initval is not supplied, NULL is used, so this is not a true foldl1. Prior to PHP 5.3, initval can only be integer. "func" is a callback. Try array_reduce online.
Python 2.x	reduce(func, list, initval)	reduce(lambda x,y: func(y,x), reversed(list), initval)	reduce(func, list)	reduce(lambda x,y: func(y,x), reversed(list))
Python 3.x	functools.reduce(func, list, initval)	functools.reduce(lambda x,y: func(y,x), reversed(list), initval)	functools.reduce(func, list)	functools.reduce(lambda x,y: func(y,x), reversed(list))		In module functools.
R	Reduce(func, list, initval)	Reduce(func, list, initval, right=TRUE)	Reduce(func, list)	Reduce(func, list, right=TRUE)		R supports right folding and left or right folding with or without an initial value through the right and init arguments to the Reduce function.
Ruby	enum.inject(initval, &block) enum.reduce(initval, &block)	enum.reverse_each.inject(initval, &block) enum.reverse_each.reduce(initval, &block)	enum.inject(&block) enum.reduce(&block)	enum.reverse_each.inject(&block) enum.reverse_each.reduce(&block)		In Ruby 1.8.7+, can also pass a symbol representing a function instead of a block. enum is an Enumeration Please notice that these implementations of right folds are wrong for non-commutative &block (also initial value is put on wrong side).
Scala	list.foldLeft(initval)(func) (initval /: list)(func)	list.foldRight(initval)(func) (list :\ initval){func}	list.reduceLeft(func)	list.reduceRight(func)		Scala's symbolic fold syntax is intended to resemble the left or right-leaning tree commonly used to explain the fold operation.
Scheme R6RS	(fold-left func initval list) (vector-fold func initval vector)	(fold-right func initval list) (vector-fold-right func initval vector)	(reduce-left func defaultval list)	(reduce-right func defaultval list)		srfi/1 srfi/43
Smalltalk	aCollection inject: aValue into: aBlock		aCollection reduce: aBlock			ANSI Smalltalk doesn't define #reduce: but many implementations do.
Standard ML	foldl func initval list Array.foldl func initval array	foldr func initval list Array.foldr func initval array				The supplied function takes its arguments in a tuple. For foldl, the folding function takes arguments in the reverse of the traditional order.
Swift	array.reduce(initval, func) reduce(sequence, initval, func)	array.reverse().reduce(initval, func)
Xtend	iterable.fold(initval,[func])		iterable.reduce[func]