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(Replaced content with "=={{header|Arturo}}== <lang rebol>; find the sum, with seed:0 (default) print fold [1 2 3 4] => (+) ; find the product, with seed:1 print fold [1 2 3 4] .seed:1 => (*) </...")
(Undo revision 324479 by Drkameleon (talk))
Line 1:
{{task}}
=={{header|Arturo}}==
<lang rebol>; find the sum, with seed:0 (default)
print fold [1 2 3 4] => (+)
 
''Reduce'' is a function or method that is used to take the values in an array or a list and apply a function to successive members of the list to produce (or reduce them to), a single value.
; find the product, with seed:1
 
print fold [1 2 3 4] .seed:1 => (*)
 
;Task:
Show how ''reduce'' (or ''foldl'' or ''foldr'' etc), work (or would be implemented) in your language.
 
 
;See also:
* Wikipedia article: &nbsp; [[wp:Fold (higher-order function)|Fold]]
* Wikipedia article: &nbsp; [[wp:Catamorphism|Catamorphism]]
<br><br>
 
=={{header|11l}}==
<lang 11l>print((1..3).reduce((x, y) -> x + y))
print((1..3).reduce(3, (x, y) -> x + y))
print([1, 1, 3].reduce((x, y) -> x + y))
print([1, 1, 3].reduce(2, (x, y) -> x + y))</lang>
{{out}}
<pre>
6
9
5
7
</pre>
 
=={{header|ABAP}}==
This works in ABAP version 7.40 and above.
 
<lang ABAP>
report z_catamorphism.
 
data(numbers) = value int4_table( ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ).
 
write: |numbers = { reduce string(
init output = `[`
index = 1
for number in numbers
next output = cond string(
when index eq lines( numbers )
then |{ output }, { number } ]|
when index > 1
then |{ output }, { number }|
else |{ output } { number }| )
index = index + 1 ) }|, /.
 
write: |sum(numbers) = { reduce int4(
init result = 0
for number in numbers
next result = result + number ) }|, /.
 
write: |product(numbers) = { reduce int4(
init result = 1
for number in numbers
next result = result * number ) }|, /.
 
data(strings) = value stringtab( ( `reduce` ) ( `in` ) ( `ABAP` ) ).
 
write: |strings = { reduce string(
init output = `[`
index = 1
for string in strings
next output = cond string(
when index eq lines( strings )
then |{ output }, { string } ]|
when index > 1
then |{ output }, { string }|
else |{ output } { string }| )
index = index + 1 ) }|, /.
 
write: |concatenation(strings) = { reduce string(
init text = ``
for string in strings
next text = |{ text } { string }| ) }|, /.
</lang>
 
{{out}}
<pre>
numbers = [ 1, 2, 3, 4, 5 ]
 
sum(numbers) = 15
 
product(numbers) = 120
 
strings = [ reduce, in, ABAP ]
 
concatenation(strings) = reduce in ABAP
</pre>
 
=={{header|Ada}}==
 
<lang Ada>with Ada.Text_IO;
 
procedure Catamorphism is
type Fun is access function (Left, Right: Natural) return Natural;
type Arr is array(Natural range <>) of Natural;
function Fold_Left (F: Fun; A: Arr) return Natural is
Result: Natural := A(A'First);
begin
for I in A'First+1 .. A'Last loop
Result := F(Result, A(I));
end loop;
return Result;
end Fold_Left;
function Max (L, R: Natural) return Natural is (if L > R then L else R);
function Min (L, R: Natural) return Natural is (if L < R then L else R);
function Add (Left, Right: Natural) return Natural is (Left + Right);
function Mul (Left, Right: Natural) return Natural is (Left * Right);
package NIO is new Ada.Text_IO.Integer_IO(Natural);
begin
NIO.Put(Fold_Left(Min'Access, (1,2,3,4)), Width => 3);
NIO.Put(Fold_Left(Max'Access, (1,2,3,4)), Width => 3);
NIO.Put(Fold_Left(Add'Access, (1,2,3,4)), Width => 3);
NIO.Put(Fold_Left(Mul'Access, (1,2,3,4)), Width => 3);
end Catamorphism;</lang>
 
{{out}}
 
<pre> 1 4 10 24</pre>
 
=={{header|Aime}}==
<lang aime>integer s;
 
s = 0;
list(1, 2, 3, 4, 5, 6, 7, 8, 9).ucall(add_i, 1, s);
o_(s, "\n");</lang>
{{Out}}
<pre>45</pre>
 
=={{header|ALGOL 68}}==
<lang algol68># applies fn to successive elements of the array of values #
# the result is 0 if there are no values #
PROC reduce = ( []INT values, PROC( INT, INT )INT fn )INT:
IF UPB values < LWB values
THEN # no elements #
0
ELSE # there are some elements #
INT result := values[ LWB values ];
FOR pos FROM LWB values + 1 TO UPB values
DO
result := fn( result, values[ pos ] )
OD;
result
FI; # reduce #
 
# test the reduce procedure #
BEGIN print( ( reduce( ( 1, 2, 3, 4, 5 ), ( INT a, b )INT: a + b ), newline ) ) # sum #
; print( ( reduce( ( 1, 2, 3, 4, 5 ), ( INT a, b )INT: a * b ), newline ) ) # product #
; print( ( reduce( ( 1, 2, 3, 4, 5 ), ( INT a, b )INT: a - b ), newline ) ) # difference #
END</lang>
{{out}}
<pre>
+15
+120
-13
</pre>
 
=={{header|AppleScript}}==
{{Trans|JavaScript}}
 
Iteratively implemented '''foldl''' and '''foldr''', using the same argument sequence as in the corresponding JavaScript array methods '''reduce()''' and '''reduceRight()'''.
 
(Note that to obtain first-class functions from user-defined AppleScript handlers, we have to 'lift' them into script objects).
 
<lang AppleScript>-- CATAMORPHISMS --------------------------------------------------
 
-- the arguments available to the called function f(a, x, i, l) are
-- a: current accumulator value
-- x: current item in list
-- i: [ 1-based index in list ] optional
-- l: [ a reference to the list itself ] optional
 
-- foldl :: (a -> b -> a) -> a -> [b] -> a
on foldl(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from 1 to lng
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldl
 
-- the arguments available to the called function f(a, x, i, l) are
-- a: current accumulator value
-- x: current item in list
-- i: [ 1-based index in list ] optional
-- l: [ a reference to the list itself ] optional
 
-- foldr :: (a -> b -> a) -> a -> [b] -> a
on foldr(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from lng to 1 by -1
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldr
 
 
-- OTHER FUNCTIONS DEFINED IN TERMS OF FOLDL AND FOLDR ------------
 
-- concat :: [[a]] -> [a] | [String] -> String
on concat(xs)
script append
on |λ|(a, b)
a & b
end |λ|
end script
if length of xs > 0 and class of (item 1 of xs) is string then
set unit to ""
else
set unit to {}
end if
foldl(append, unit, xs)
end concat
 
-- product :: Num a => [a] -> a
on product(xs)
script
on |λ|(a, b)
a * b
end |λ|
end script
foldr(result, 1, xs)
end product
 
-- sum :: Num a => [a] -> a
on sum(xs)
script
on |λ|(a, b)
a + b
end |λ|
end script
foldl(result, 0, xs)
end sum
 
 
-- TEST -----------------------------------------------------------
on run
set xs to {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
{sum(xs), product(xs), concat(xs)}
--> {55, 3628800, "10987654321"}
end run
 
 
-- GENERIC FUNCTION -----------------------------------------------
 
-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn</lang>
{{out}}
<pre>{55, 3628800, "10987654321"}</pre>
 
=={{header|BBC BASIC}}==
<lang bbcbasic>
DIM a(4)
a() = 1, 2, 3, 4, 5
PRINT FNreduce(a(), "+")
PRINT FNreduce(a(), "-")
PRINT FNreduce(a(), "*")
END
 
DEF FNreduce(arr(), op$)
REM!Keep tmp, arr()
LOCAL I%, tmp
tmp = arr(0)
FOR I% = 1 TO DIM(arr(), 1)
tmp = EVAL("tmp " + op$ + " arr(I%)")
NEXT
= tmp
</lang>
 
{{out}}
<pre> 15
-13
120</pre>
 
=={{header|Bracmat}}==
<lang bracmat>( ( fold
= f xs init first rest
. !arg:(?f.?xs.?init)
& ( !xs:&!init
| !xs:%?first ?rest
& !f$(!first.fold$(!f.!rest.!init))
)
)
& out
$ ( fold
$ ( (=a b.!arg:(?a.?b)&!a+!b)
. 1 2 3 4 5
. 0
)
)
& (product=a b.!arg:(?a.?b)&!a*!b)
& out$(fold$(product.1 2 3 4 5.1))
);</lang>
Output:
<pre>15
120</pre>
 
=={{header|C}}==
<lang C>#include <stdio.h>
 
typedef int (*intFn)(int, int);
 
int reduce(intFn fn, int size, int *elms)
{
int i, val = *elms;
for (i = 1; i < size; ++i)
val = fn(val, elms[i]);
return val;
}
 
int add(int a, int b) { return a + b; }
int sub(int a, int b) { return a - b; }
int mul(int a, int b) { return a * b; }
 
int main(void)
{
int nums[] = {1, 2, 3, 4, 5};
printf("%d\n", reduce(add, 5, nums));
printf("%d\n", reduce(sub, 5, nums));
printf("%d\n", reduce(mul, 5, nums));
return 0;
}</lang>
 
{{out}}
<pre>15
-13
120</pre>
 
=={{header|C sharp}}==
<lang csharp>var nums = Enumerable.Range(1, 10);
 
int summation = nums.Aggregate((a, b) => a + b);
 
int product = nums.Aggregate((a, b) => a * b);
 
string concatenation = nums.Aggregate(String.Empty, (a, b) => a.ToString() + b.ToString());
 
Console.WriteLine("{0} {1} {2}", summation, product, concatenation);</lang>
 
=={{header|C++}}==
<lang cpp>#include <iostream>
#include <numeric>
#include <functional>
#include <vector>
 
int main() {
std::vector<int> nums = { 1, 2, 3, 4, 5 };
auto nums_added = std::accumulate(std::begin(nums), std::end(nums), 0, std::plus<int>());
auto nums_other = std::accumulate(std::begin(nums), std::end(nums), 0, [](const int& a, const int& b) {
return a + 2 * b;
});
std::cout << "nums_added: " << nums_added << std::endl;
std::cout << "nums_other: " << nums_other << std::endl;
}</lang>
 
{{out}}
 
<pre>nums_added: 15
nums_other: 30</pre>
 
=={{header|Clojure}}==
For more detail, check Rich Hickey's [http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection-processing.html blog post on Reducers].
 
<lang clojure>; Basic usage
> (reduce * '(1 2 3 4 5))
120
; Using an initial value
> (reduce + 100 '(1 2 3 4 5))
115
</lang>
 
=={{header|Common Lisp}}==
<lang lisp>; Basic usage
> (reduce #'* '(1 2 3 4 5))
120
; Using an initial value
> (reduce #'+ '(1 2 3 4 5) :initial-value 100)
115
; Using only a subsequence
> (reduce #'+ '(1 2 3 4 5) :start 1 :end 4)
9
; Apply a function to each element first
> (reduce #'+ '((a 1) (b 2) (c 3)) :key #'cadr)
6
; Right-associative reduction
> (reduce #'expt '(2 3 4) :from-end T)
2417851639229258349412352
; Compare with
> (reduce #'expt '(2 3 4))
4096</lang>
 
=={{header|D}}==
<lang d>void main() {
import std.stdio, std.algorithm, std.range, std.meta, std.numeric,
std.conv, std.typecons;
 
auto list = iota(1, 11);
alias ops = AliasSeq!(q{a + b}, q{a * b}, min, max, gcd);
 
foreach (op; ops)
writeln(op.stringof, ": ", list.reduce!op);
 
// std.algorithm.reduce supports multiple functions in parallel:
reduce!(ops[0], ops[3], text)(tuple(0, 0.0, ""), list).writeln;
}</lang>
{{out}}
<pre>"a + b": 55
"a * b": 3628800
min(T1,T2,T...) if (is(typeof(a < b))): 1
max(T1,T2,T...) if (is(typeof(a < b))): 10
gcd(T): 1
Tuple!(int,double,string)(55, 10, "12345678910")</pre>
 
=={{header|DCL}}==
<lang DCL>$ list = "1,2,3,4,5"
$ call reduce list "+"
$ show symbol result
$
$ numbers = "5,4,3,2,1"
$ call reduce numbers "-"
$ show symbol result
$
$ call reduce list "*"
$ show symbol result
$ exit
$
$ reduce: subroutine
$ local_list = 'p1
$ value = f$integer( f$element( 0, ",", local_list ))
$ i = 1
$ loop:
$ element = f$element( i, ",", local_list )
$ if element .eqs. "," then $ goto done
$ value = value 'p2 f$integer( element )
$ i = i + 1
$ goto loop
$ done:
$ result == value
$ exit
$ endsubroutine</lang>
{{out}}
<pre>$ @catamorphism
RESULT == 15 Hex = 0000000F Octal = 00000000017
RESULT == -5 Hex = FFFFFFFB Octal = 37777777773
RESULT == 120 Hex = 00000078 Octal = 00000000170</pre>
 
=={{header|Déjà Vu}}==
This is a foldl:
<lang dejavu>reduce f lst init:
if lst:
f reduce @f lst init pop-from lst
else:
init
 
!. reduce @+ [ 1 10 200 ] 4
!. reduce @- [ 1 10 200 ] 4
</lang>
{{out}}
<pre>215
-207</pre>
 
=={{header|EchoLisp}}==
<lang scheme>
;; rem : the foldX family always need an initial value
;; fold left a list
(foldl + 0 (iota 10)) ;; 0 + 1 + .. + 9
→ 45
 
;; fold left a sequence
(lib 'sequences)
(foldl * 1 [ 1 .. 10])
→ 362880 ;; 10!
 
;; folding left and right
(foldl / 1 ' ( 1 2 3 4))
→ 8/3
(foldr / 1 '(1 2 3 4))
→ 3/8
 
;;scanl gives the list (or sequence) of intermediate values :
(scanl * 1 '( 1 2 3 4 5))
→ (1 1 2 6 24 120)
</lang>
 
=={{header|Elena}}==
ELENA 5.0 :
<lang elena>import system'collections;
import system'routines;
import extensions;
import extensions'text;
public program()
{
var numbers := new Range(1,10).summarize(new ArrayList());
var summary := numbers.accumulate(new Variable(0), (a,b => a + b));
var product := numbers.accumulate(new Variable(1), (a,b => a * b));
var concatenation := numbers.accumulate(new StringWriter(), (a,b => a.toPrintable() + b.toPrintable()));
console.printLine(summary," ",product," ",concatenation)
}</lang>
{{out}}
<pre>
55 362880 12345678910
</pre>
 
=={{header|Elixir}}==
<lang elixir>iex(1)> Enum.reduce(1..10, fn i,acc -> i+acc end)
55
iex(2)> Enum.reduce(1..10, fn i,acc -> i*acc end)
3628800
iex(3)> Enum.reduce(10..-10, "", fn i,acc -> acc <> to_string(i) end)
"109876543210-1-2-3-4-5-6-7-8-9-10"</lang>
 
=={{header|Erlang}}==
{{trans|Haskell}}
 
<lang erlang>
-module(catamorphism).
 
-export([test/0]).
 
test() ->
Nums = lists:seq(1,10),
Summation =
lists:foldl(fun(X, Acc) -> X + Acc end, 0, Nums),
Product =
lists:foldl(fun(X, Acc) -> X * Acc end, 1, Nums),
Concatenation =
lists:foldr(
fun(X, Acc) -> integer_to_list(X) ++ Acc end,
"",
Nums),
{Summation, Product, Concatenation}.
</lang>
 
Output:
<pre>
{55,3628800,"12345678910"}
</pre>
 
=={{header|F_Sharp|F#}}==
<p>In the REPL:</p>
<pre>
> let nums = [1 .. 10];;
 
val nums : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
 
> let summation = List.fold (+) 0 nums;;
 
val summation : int = 55
 
> let product = List.fold (*) 1 nums;;
 
val product : int = 3628800
 
> let concatenation = List.foldBack (fun x y -> x + y) (List.map (fun i -> i.ToString()) nums) "";;
 
val concatenation : string = "12345678910"
</pre>
 
=={{header|Factor}}==
 
<lang factor>{ 1 2 4 6 10 } 0 [ + ] reduce .</lang>
{{out}}
<pre>
23
</pre>
 
=={{header|Forth}}==
Forth has three traditions for iterating over the members of a data
structure. Under the first, the data structure has words that help
you navigate over it and normal Forth looping structures are used.
Under the second, the data structure has dedicated looping words and
you supply the code that's run for each member. Under the third,
the data structure has a loop-over-members word that accepts a
function to be run against each member.
 
There's no need to distinguish between the different kinds of
looping ("this one collects function returns into a list; this one
threads an accumulator between the function-calls; this one threads
two accumulators through the function-calls; this one expects no
return values whatsoever from the function-calls") because in Forth
all that the looping words have to do is make the data stack
available for the function's use. When that's the case, all of
these variations, that are so important in other languages, are
functionally equivalent.
 
Although it's possible to have a generic higher-order word that can
operate under all kinds of data structures -- this just requires
that one settle on an object system and then derive a collections
library from it -- this is rarely done. Typically each data
structure has its own looping words.
 
To demonstrate the above points we'll just loop over the bytes of a
string.
 
Some helper words for these examples:
 
<lang forth>: lowercase? ( c -- f )
[char] a [ char z 1+ ] literal within ;
 
: char-upcase ( c -- C )
dup lowercase? if bl xor then ;</lang>
 
Using normal looping words:
 
<lang forth>: string-at ( c-addr u +n -- c )
nip + c@ ;
: string-at! ( c-addr u +n c -- )
rot drop -rot + c! ;
 
: type-lowercase ( c-addr u -- )
dup 0 ?do
2dup i string-at dup lowercase? if emit else drop then
loop 2drop ;
 
: upcase ( 'string' -- 'STRING' )
dup 0 ?do
2dup 2dup i string-at char-upcase i swap string-at!
loop ;
 
: count-lowercase ( c-addr u -- n )
0 -rot dup 0 ?do
2dup i string-at lowercase? if rot 1+ -rot then
loop 2drop ;</lang>
 
Briefly, a variation:
 
<lang forth>: next-char ( a +n -- a' n' c -1 ) ( a 0 -- 0 )
dup if 2dup 1 /string 2swap drop c@ true
else 2drop 0 then ;
 
: type-lowercase ( c-addr u -- )
begin next-char while
dup lowercase? if emit else drop then
repeat ;</lang>
 
Using dedicated looping words:
 
<lang forth>: each-char[ ( c-addr u -- )
postpone BOUNDS postpone ?DO
postpone I postpone C@ ; immediate
 
\ interim code: ( c -- )
 
: ]each-char ( -- )
postpone LOOP ; immediate
 
: type-lowercase ( c-addr u -- )
each-char[ dup lowercase? if emit else drop then ]each-char ;
 
: upcase ( 'string' -- 'STRING' )
2dup each-char[ char-upcase i c! ]each-char ;
 
: count-lowercase ( c-addr u -- n )
0 -rot each-char[ lowercase? if 1+ then ]each-char ;</lang>
 
Using higher-order words:
 
<lang forth>: each-char ( c-addr u xt -- )
{: xt :} bounds ?do
i c@ xt execute
loop ;
 
: type-lowercase ( c-addr u -- )
[: dup lowercase? if emit else drop then ;]
each-char ;
 
\ producing a new string
: upcase ( 'string' -- 'STRING' )
dup cell+ allocate throw -rot
[: ( new-string-addr c -- new-string-addr )
upcase over c+! ;] each-char $@ ;
 
: count-lowercase ( c-addr u -- n )
0 -rot [: lowercase? if 1+ then ;] each-char ;</lang>
 
In these examples COUNT-LOWERCASE updates an accumulator, UPCASE
(mostly) modifies the string in-place, and TYPE-LOWERCASE performs
side-effects and returns nothing to the higher-order word.
 
=={{header|Fortran}}==
If Fortran were to offer the ability to pass a parameter "by name", as is used in [[Jensen's_Device#Fortran|Jensen's device]], then the code might be something like <lang Fortran> SUBROUTINE FOLD(t,F,i,ist,lst)
INTEGER t
BYNAME F
DO i = ist,lst
t = F
END DO
END SUBROUTINE FOLD !Result in temp.
 
temp = a(1); CALL FOLD(temp,temp*a(i),i,2,N)</lang>
Here, the function manifests as the expression that is the second parameter of subroutine FOLD, and the "by name" protocol for parameter F means that within the subroutine whenever there is a reference to F, its value is evaluated afresh in the caller's environment using the current values of ''temp'' and ''i'' as modified by the subroutine - they being passed by reference so that changes within the subroutine affect the originals. An evaluation for a different function requires merely another statement with a different expression.
 
Fortran however does not provide such a facility. Any parameter that is an expression is evaluated once in the caller's environment, the result placed in temporary storage, and the address of that storage location is passed to the subroutine. Repeated references to that parameter will elicit the same value. But there is special provision for passing a function to a routine, involving the special word EXTERNAL. For every different function in mind, one must diligently supply a name, and work through the overhead of declaring each such function. There is an additional word, INTRINSIC, for use when an intrinsic function (such as SIN) is to be passed as such a parameter since it will appear as its name only, and with the absence of the (...) that would be used for the function's parameters when in an arithmetic expression, it would otherwise be taken as being the name of an ordinary variable.
 
Here is such an arrangement, in the style of F77 though somewhat affected by F90 in that the END statement names the routine being ended. Similarly, to abate petty complaints about the types of the functions being undeclared, explicit types are specified, though unselecting the compiler diagnostic for that would match the habits of earlier compilers. Also in F90 is the MODULE protocol which involves rather more organised checking of types and additional facilities for arrays [[Array_length#Fortran|so that N need not be passed]] because secret additional parameters do so.
 
However, only programmer diligence in devising functions with the correct type of result and the correct type and number of parameters will evade mishaps. Note that the EXTERNAL statement does not specify the number or type of parameters. If the function is invoked multiple times within a subroutine, the compiler may check for consistency. This may cause trouble when [[Leonardo_numbers#Fortran|some parameters are optional]] so that different invocations do not match.
 
The function's name is used as a working variable within the function (as well as it holding the function's value on exit) so that the expression <code>F(IFOLD,A(I))</code> is ''not'' a recursive invocation of function <code>IFOLD</code> because there are no (parameters) appended to the function's name. Earlier compilers did not allow such usage so that a separate working variable would be required. <lang Fortran> INTEGER FUNCTION IFOLD(F,A,N) !"Catamorphism"...
INTEGER F !We're working only with integers.
EXTERNAL F !This is a function, not an array.
INTEGER A(*) !An 1-D array, of unspecified size.
INTEGER N !The number of elements.
INTEGER I !A stepper.
IFOLD = 0 !A default value.
IF (N.LE.0) RETURN !Dodge silly invocations.
IFOLD = A(1) !The function is to have two arguments.
IF (N.EQ.1) RETURN !So, if there is only one element, silly.
DO I = 2,N !Otherwise, stutter along the array.
IFOLD = F(IFOLD,A(I)) !Applying the function.
END DO !On to the next element.
END FUNCTION IFOLD!Thus, F(A(1),A(2)), or F(F(A(1),A(2)),A(3)), or F(F(F(A(1),A(2)),A(3)),A(4)), etc.
 
INTEGER FUNCTION IADD(I,J)
INTEGER I,J
IADD = I + J
END FUNCTION IADD
 
INTEGER FUNCTION IMUL(I,J)
INTEGER I,J
IMUL = I*J
END FUNCTION IMUL
 
INTEGER FUNCTION IDIV(I,J)
INTEGER I,J
IDIV = I/J
END FUNCTION IDIV
 
INTEGER FUNCTION IVID(I,J)
INTEGER I,J
IVID = J/I
END FUNCTION IVID
 
PROGRAM POKE
INTEGER ENUFF
PARAMETER (ENUFF = 6)
INTEGER A(ENUFF)
PARAMETER (A = (/1,2,3,4,5,6/))
INTEGER MSG
EXTERNAL IADD,IMUL,IDIV,IVID !Warn that these are the names of functions.
 
MSG = 6 !Standard output.
WRITE (MSG,1) ENUFF,A
1 FORMAT ('To apply a function in the "catamorphic" style ',
1 "to the ",I0," values ",/,(20I3))
 
WRITE (MSG,*) "Iadd",IFOLD(IADD,A,ENUFF)
WRITE (MSG,*) "Imul",IFOLD(IMUL,A,ENUFF)
WRITE (MSG,*) "Idiv",IFOLD(IDIV,A,ENUFF)
WRITE (MSG,*) "Ivid",IFOLD(IVID,A,ENUFF)
END PROGRAM POKE
</lang>
Output:
<pre>
To apply a function in the "catamorphic" style to the 6 values
1 2 3 4 5 6
Iadd 21
Imul 720
Idiv 0
Ivid 6
</pre>
 
=={{header|FreeBASIC}}==
<lang freebasic>' FB 1.05.0 Win64
 
Type IntFunc As Function(As Integer, As Integer) As Integer
Function reduce(a() As Integer, f As IntFunc) As Integer
'' if array is empty or function pointer is null, return 0 say
If UBound(a) = -1 OrElse f = 0 Then Return 0
Dim result As Integer = a(LBound(a))
For i As Integer = LBound(a) + 1 To UBound(a)
result = f(result, a(i))
Next
Return result
End Function
 
Function add(x As Integer, y As Integer) As Integer
Return x + y
End Function
 
Function subtract(x As Integer, y As Integer) As Integer
Return x - y
End Function
 
Function multiply(x As Integer, y As Integer) As Integer
Return x * y
End Function
 
Function max(x As Integer, y As Integer) As Integer
Return IIf(x > y, x, y)
End Function
 
Function min(x As Integer, y As Integer) As Integer
Return IIf(x < y, x, y)
End Function
 
Dim a(4) As Integer = {1, 2, 3, 4, 5}
Print "Sum is :"; reduce(a(), @add)
Print "Difference is :"; reduce(a(), @subtract)
Print "Product is :"; reduce(a(), @multiply)
Print "Maximum is :"; reduce(a(), @max)
Print "Minimum is :"; reduce(a(), @min)
Print "No op is :"; reduce(a(), 0)
Print
Print "Press any key to quit"
Sleep
</lang>
 
{{out}}
<pre>
Sum is : 15
Difference is :-13
Product is : 120
Maximum is : 5
Minimum is : 1
No op is : 0
</pre>
 
=={{header|Go}}==
<lang go>package main
 
import (
"fmt"
)
 
func main() {
n := []int{1, 2, 3, 4, 5}
 
fmt.Println(reduce(add, n))
fmt.Println(reduce(sub, n))
fmt.Println(reduce(mul, n))
}
 
func add(a int, b int) int { return a + b }
func sub(a int, b int) int { return a - b }
func mul(a int, b int) int { return a * b }
 
func reduce(rf func(int, int) int, m []int) int {
r := m[0]
for _, v := range m[1:] {
r = rf(r, v)
}
return r
}</lang>
{{out}}
<pre>
15
-13
120
</pre>
 
=={{header|Groovy}}==
Groovy provides an "inject" method for all aggregate classes that performs a classic tail-recursive reduction, driven by a closure argument. The result of each iteration (closure invocation) is used as the accumulated valued for the next iteration. If a first argument is provided as well as a second closure argument, that first argument is used as a seed accumulator for the first iteration. Otherwise, the first element of the aggregate is used as the seed accumulator, with reduction iteration proceeding across elements 2 through n.
<lang groovy>def vector1 = [1,2,3,4,5,6,7]
def vector2 = [7,6,5,4,3,2,1]
def map1 = [a:1, b:2, c:3, d:4]
 
println vector1.inject { acc, val -> acc + val } // sum
println vector1.inject { acc, val -> acc + val*val } // sum of squares
println vector1.inject { acc, val -> acc * val } // product
println vector1.inject { acc, val -> acc<val?val:acc } // max
println ([vector1,vector2].transpose().inject(0) { acc, val -> acc + val[0]*val[1] }) //dot product (with seed 0)
 
println (map1.inject { Map.Entry accEntry, Map.Entry entry -> // some sort of weird map-based reduction
[(accEntry.key + entry.key):accEntry.value + entry.value ].entrySet().toList().pop()
})</lang>
 
{{out}}
<pre>28
140
5040
7
84
abcd=10</pre>
 
=={{header|Haskell}}==
<lang haskell>main :: IO ()
main =
putStrLn . unlines $
[ show . foldr (+) 0 -- sum
, show . foldr (*) 1 -- product
, foldr ((++) . show) "" -- concatenation
] <*>
[[1 .. 10]]</lang>
{{Out}}
<pre>55
3628800
12345678910</pre>
 
and the generality of folds is such that if we replace all three of these (function, identity) combinations ((+), 0), ((*), 1) ((++), "") with the Monoid operation '''mappend''' (<>) and identity '''mempty''', we can still obtain the same results:
 
<lang haskell>import Data.Monoid
 
main :: IO ()
main =
let xs = [1 .. 10]
in (putStrLn . unlines)
[ (show . getSum . foldr (<>) mempty) (Sum <$> xs)
, (show . getProduct . foldr (<>) mempty) (Product <$> xs)
, (show . foldr (<>) mempty) (show <$> xs)
, (show . foldr (<>) mempty) (words
"Love is one damned thing after each other")
]</lang>
{{Out}}
<pre>55
3628800
"12345678910"
"Loveisonedamnedthingaftereachother"</pre>
 
Also available are ''foldl1'' and ''foldr1'' which implicitly take first element as starting value. However they are not safe as they fail on empty lists.
 
''Prelude'' folds work only on lists, module ''Data.Foldable'' a typeclass for more general fold - interface remains the same.
 
=={{header|Icon}} and {{header|Unicon}}==
 
Works in both languages:
<lang unicon>procedure main(A)
write(A[1],": ",curry(A[1],A[2:0]))
end
 
procedure curry(f,A)
r := A[1]
every r := f(r, !A[2:0])
return r
end</lang>
 
Sample runs:
<pre>
->cata + 3 1 4 1 5 9
+: 23
->cata - 3 1 4 1 5 9
-: -17
->cata \* 3 1 4 1 5 9
*: 540
->cata "||" 3 1 4 1 5 9
||: 314159
</pre>
 
=={{header|J}}==
'''Solution''':<lang j> /</lang>
'''Example''':<lang j> +/ 1 2 3 4 5
15
*/ 1 2 3 4 5
120
!/ 1 2 3 4 5 NB. "n ! k" is "n choose k"
45</lang>
Insert * into 1 2 3 4 5
becomes
1 * 2 * 3 * 4 * 5
evaluated right to left<lang j>
1 * 2 * 3 * 20
1 * 2 * 60
1 * 120
120
</lang>
What are the implications for -/ ?
For %/ ?
 
=={{header|Java}}==
{{works with|Java|8}}
<lang java>import java.util.stream.Stream;
 
public class ReduceTask {
 
public static void main(String[] args) {
System.out.println(Stream.of(1, 2, 3, 4, 5).mapToInt(i -> i).sum());
System.out.println(Stream.of(1, 2, 3, 4, 5).reduce(1, (a, b) -> a * b));
}
}</lang>
 
{{out}}
<pre>15
120</pre>
 
=={{header|JavaScript}}==
 
===ES5===
 
<lang javascript>var nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
function add(a, b) {
return a + b;
}
 
var summation = nums.reduce(add);
 
function mul(a, b) {
return a * b;
}
 
var product = nums.reduce(mul, 1);
 
var concatenation = nums.reduce(add, "");
 
console.log(summation, product, concatenation);</lang>
 
 
Note that the JavaScript Array methods include a right fold ( '''.reduceRight()''' ) as well as a left fold:
 
<lang JavaScript>(function (xs) {
'use strict';
 
// foldl :: (b -> a -> b) -> b -> [a] -> b
function foldl(f, acc, xs) {
return xs.reduce(f, acc);
}
 
// foldr :: (b -> a -> b) -> b -> [a] -> b
function foldr(f, acc, xs) {
return xs.reduceRight(f, acc);
}
 
// Test folds in both directions
return [foldl, foldr].map(function (f) {
return f(function (acc, x) {
return acc + (x * 2).toString() + ' ';
}, [], xs);
});
 
})([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);</lang>
 
{{Out}}
 
<pre>["0 2 4 6 8 10 12 14 16 18 ",
"18 16 14 12 10 8 6 4 2 0 "]</pre>
 
===ES6===
 
<lang javascript>var nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
console.log(nums.reduce((a, b) => a + b, 0)); // sum of 1..10
console.log(nums.reduce((a, b) => a * b, 1)); // product of 1..10
console.log(nums.reduce((a, b) => a + b, '')); // concatenation of 1..10</lang>
 
=={{header|jq}}==
jq has an unusual and unusually powerful "reduce" control structure. A full description is beyond the scope of this short article, but an important point is that "reduce" is stream-oriented. Reduction of arrays is however trivially achieved using the ".[]" filter for converting an array to a stream of its values.
 
The simplest use of "reduce" can be illustrated by this definition of "factorial":
 
def factorial: reduce range(2;.+1) as $i (1; . * $i);
 
If the input is a non-negative integer, n, this will compute n!.
 
To understand how this works, consider "3|factorial". The computation starts by setting the implicit state variable to 1; range(2;4) will generate the sequence of values (2,3). The variable $i is set to each value in the stream in turn so that the state variable is multiplied by 2 (". * $i") and then by 3. Notice that since range/2 produces a stream, no array is ever constructed.
 
For a more complex illustration, see [[Sorting_algorithms/Strand_sort#jq|Strand sort]].
 
The "reduce" operator is typically used within a map/reduce framework, but the implicit state variable can be any JSON entity, and so "reduce" is also a general-purpose iterative control structure, the only limitation being that it does not have the equivalent of "break". For that, the "foreach" control structure in recent versions of jq can be used.
 
=={{header|Julia}}==
{{Works with|Julia 1.2}}
<lang Julia>println([reduce(op, 1:5) for op in [+, -, *]])
println([foldl(op, 1:5) for op in [+, -, *]])
println([foldr(op, 1:5) for op in [+, -, *]])</lang>
{{out}}
<pre>[15, -13, 120]
[15, -13, 120]
[15, 3, 120]</pre>
 
=={{header|Kotlin}}==
<lang scala>fun main(args: Array<String>) {
val a = intArrayOf(1, 2, 3, 4, 5)
println("Array : ${a.joinToString(", ")}")
println("Sum : ${a.reduce { x, y -> x + y }}")
println("Difference : ${a.reduce { x, y -> x - y }}")
println("Product : ${a.reduce { x, y -> x * y }}")
println("Minimum : ${a.reduce { x, y -> if (x < y) x else y }}")
println("Maximum : ${a.reduce { x, y -> if (x > y) x else y }}")
}</lang>
 
{{out}}
<pre>
Array : 1, 2, 3, 4, 5
Sum : 15
Difference : -13
Product : 120
Minimum : 1
Maximum : 5
</pre>
 
=={{header|Logtalk}}==
The Logtalk standard library provides implementations of common meta-predicates such as fold left. The example that follow uses Logtalk's native support for lambda expressions to avoid the need for auxiliary predicates.
<lang logtalk>
:- object(folding_examples).
 
:- public(show/0).
show :-
integer::sequence(1, 10, List),
write('List: '), write(List), nl,
meta::fold_left([Acc,N,Sum0]>>(Sum0 is Acc+N), 0, List, Sum),
write('Sum of all elements: '), write(Sum), nl,
meta::fold_left([Acc,N,Product0]>>(Product0 is Acc*N), 1, List, Product),
write('Product of all elements: '), write(Product), nl,
meta::fold_left([Acc,N,Concat0]>>(number_codes(N,NC), atom_codes(NA,NC), atom_concat(Acc,NA,Concat0)), '', List, Concat),
write('Concatenation of all elements: '), write(Concat), nl.
 
:- end_object.
</lang>
{{out}}
<pre>
| ?- folding_examples::show.
List: [1,2,3,4,5,6,7,8,9,10]
Sum of all elements: 55
Product of all elements: 3628800
Concatenation of all elements: 12345678910
yes
</pre>
 
=={{header|LOLCODE}}==
 
{{trans|C}}
 
<lang LOLCODE>HAI 1.3
 
HOW IZ I reducin YR array AN YR size AN YR fn
I HAS A val ITZ array'Z SRS 0
IM IN YR loop UPPIN YR i TIL BOTH SAEM i AN DIFF OF size AN 1
val R I IZ fn YR val AN YR array'Z SRS SUM OF i AN 1 MKAY
IM OUTTA YR loop
FOUND YR val
IF U SAY SO
 
O HAI IM array
I HAS A SRS 0 ITZ 1
I HAS A SRS 1 ITZ 2
I HAS A SRS 2 ITZ 3
I HAS A SRS 3 ITZ 4
I HAS A SRS 4 ITZ 5
KTHX
 
HOW IZ I add YR a AN YR b, FOUND YR SUM OF a AN b, IF U SAY SO
HOW IZ I sub YR a AN YR b, FOUND YR DIFF OF a AN b, IF U SAY SO
HOW IZ I mul YR a AN YR b, FOUND YR PRODUKT OF a AN b, IF U SAY SO
 
VISIBLE I IZ reducin YR array AN YR 5 AN YR add MKAY
VISIBLE I IZ reducin YR array AN YR 5 AN YR sub MKAY
VISIBLE I IZ reducin YR array AN YR 5 AN YR mul MKAY
 
KTHXBYE</lang>
 
{{out}}
<pre>15
-13
120</pre>
 
=={{header|Lua}}==
<lang Lua>
table.unpack = table.unpack or unpack -- 5.1 compatibility
local nums = {1,2,3,4,5,6,7,8,9}
 
function add(a,b)
return a+b
end
 
function mult(a,b)
return a*b
end
 
function cat(a,b)
return tostring(a)..tostring(b)
end
 
local function reduce(fun,a,b,...)
if ... then
return reduce(fun,fun(a,b),...)
else
return fun(a,b)
end
end
 
local arithmetic_sum = function (...) return reduce(add,...) end
local factorial5 = reduce(mult,5,4,3,2,1)
 
print("Σ(1..9) : ",arithmetic_sum(table.unpack(nums)))
print("5! : ",factorial5)
print("cat {1..9}: ",reduce(cat,table.unpack(nums)))
 
</lang>
 
{{out}}
<pre>
Σ(1..9) : 45
5! : 120
cat {1..9}: 123456789
</pre>
 
=={{header|M2000 Interpreter}}==
<lang M2000 Interpreter>
Module CheckIt {
Function Reduce (a, f) {
if len(a)=0 then Error "Nothing to reduce"
if len(a)=1 then =Array(a) : Exit
k=each(a, 2, -1)
m=Array(a)
While k {
m=f(m, array(k))
}
=m
}
a=(1, 2, 3, 4, 5)
Print "Array", a
Print "Sum", Reduce(a, lambda (x,y)->x+y)
Print "Difference", Reduce(a, lambda (x,y)->x-y)
Print "Product", Reduce(a, lambda (x,y)->x*y)
Print "Minimum", Reduce(a, lambda (x,y)->if(x<y->x, y))
Print "Maximum", Reduce(a, lambda (x,y)->if(x>y->x, y))
}
CheckIt
</lang>
{{out}}
<pre>
Array 1 2 3 4 5
Sum 15
Difference -13
Product 120
Minimum 1
Maximum 5
</pre>
 
=={{header|Maple}}==
The left fold operator in Maple is foldl, and foldr is the right fold operator.
<lang Maple>> nums := seq( 1 .. 10 );
nums := 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
 
> foldl( `+`, 0, nums ); # compute sum using foldl
55
 
> foldr( `*`, 1, nums ); # compute product using foldr
3628800</lang>
Compute the horner form of a (sorted) polynomial:
<lang Maple>> foldl( (a,b) ->a*T+b, op(map2(op,1,[op( 72*T^5+37*T^4-23*T^3+87*T^2+44*T+29 )])));
((((72 T + 37) T - 23) T + 87) T + 44) T + 29</lang>
 
=={{header|Mathematica}} / {{header|Wolfram Language}}==
<lang mathematica>Fold[f, x, {a, b, c, d}]</lang>
{{Out}}
<pre>f[f[f[f[x, a], b], c], d]</pre>
 
=={{header|Maxima}}==
<lang maxima>lreduce(f, [a, b, c, d], x0);
/* (%o1) f(f(f(f(x0, a), b), c), d) */</lang>
 
<lang maxima>lreduce("+", [1, 2, 3, 4], 100);
/* (%o1) 110 */</lang>
 
=={{header|min}}==
{{works with|min|0.19.3}}
<lang min>(1 2 3 4) 0 '+ reduce puts! ; sum
(1 2 3 4) 1 '* reduce puts! ; product</lang>
{{out}}
<pre>
10
24
</pre>
 
=={{header|Nemerle}}==
The <tt>Nemerle.Collections</tt> namespace defines <tt>FoldLeft</tt>, <tt>FoldRight</tt> and <tt>Fold</tt> (an alias for <tt>FoldLeft</tt>) on any sequence that implements the <tt>IEnumerable[T]</tt> interface.
<lang Nemerle>def seq = [1, 4, 6, 3, 7];
def sum = seq.Fold(0, _ + _); // Fold takes an initial value and a function, here the + operator</lang>
 
=={{header|Nim}}==
<lang nim>import sequtils
 
block:
let
numbers = @[5, 9, 11]
addition = foldl(numbers, a + b)
substraction = foldl(numbers, a - b)
multiplication = foldl(numbers, a * b)
words = @["nim", "is", "cool"]
concatenation = foldl(words, a & b)
 
block:
let
numbers = @[5, 9, 11]
addition = foldr(numbers, a + b)
substraction = foldr(numbers, a - b)
multiplication = foldr(numbers, a * b)
words = @["nim", "is", "cool"]
concatenation = foldr(words, a & b)</lang>
 
=={{header|Oberon-2}}==
{{Works with| oo2c Version 2}}
<lang oberon2>
MODULE Catamorphism;
IMPORT
Object,
NPCT:Tools,
NPCT:Args,
IntStr,
Out;
TYPE
BinaryFunc= PROCEDURE (x,y: LONGINT): LONGINT;
VAR
data: POINTER TO ARRAY OF LONGINT;
i: LONGINT;
 
PROCEDURE Sum(x,y: LONGINT): LONGINT;
BEGIN
RETURN x + y
END Sum;
PROCEDURE Sub(x,y: LONGINT): LONGINT;
BEGIN
RETURN x - y;
END Sub;
PROCEDURE Mul(x,y: LONGINT): LONGINT;
BEGIN
RETURN x * y;
END Mul;
PROCEDURE Reduce(x: ARRAY OF LONGINT; f: BinaryFunc): LONGINT;
VAR
i,res: LONGINT;
BEGIN
res := x[0];i := 1;
WHILE (i < LEN(x)) DO;
res := f(res,x[i]);
INC(i)
END;
RETURN res
END Reduce;
PROCEDURE InitData(VAR x: ARRAY OF LONGINT);
VAR
i, j: LONGINT;
res: IntStr.ConvResults;
aux: Object.CharsLatin1;
BEGIN
i := 0;j := 1;
WHILE (j <= LEN(x)) DO
aux := Tools.AsString(Args.Get(j));
IntStr.StrToInt(aux^,x[i],res);
IF res # IntStr.strAllRight THEN
Out.String("Incorrect format for data at index ");Out.LongInt(j,0);Out.Ln;
HALT(1);
END;
INC(j);INC(i)
END
END InitData;
BEGIN
IF Args.Number() = 1 THEN
Out.String("Invalid number of arguments. ");Out.Ln;
HALT(0)
ELSE
NEW(data,Args.Number() - 1);
InitData(data^);
Out.LongInt(Reduce(data^,Sum),0);Out.Ln;
Out.LongInt(Reduce(data^,Sub),0);Out.Ln;
Out.LongInt(Reduce(data^,Mul),0);Out.Ln
END
END Catamorphism.
</lang>
{{out}}
<pre>
1
-11
-14400
</pre>
 
=={{header|Objeck}}==
<lang objeck>
use Collection;
 
class Reducer {
function : Main(args : String[]) ~ Nil {
values := IntVector->New([1, 2, 3, 4, 5]);
values->Reduce(Add(Int, Int) ~ Int)->PrintLine();
values->Reduce(Mul(Int, Int) ~ Int)->PrintLine();
}
 
function : Add(a : Int, b : Int) ~ Int {
return a + b;
}
function : Mul(a : Int, b : Int) ~ Int {
return a * b;
}
}</lang>
Output
<pre>
15
120
</pre>
 
=={{header|OCaml}}==
<lang ocaml># let nums = [1;2;3;4;5;6;7;8;9;10];;
val nums : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
# let sum = List.fold_left (+) 0 nums;;
val sum : int = 55
# let product = List.fold_left ( * ) 1 nums;;
val product : int = 3628800</lang>
 
=={{header|Oforth}}==
reduce is already defined into Collection class :
 
<lang Oforth>[ 1, 2, 3, 4, 5 ] reduce(#max)
[ "abc", "def", "gfi" ] reduce(#+)</lang>
 
=={{header|PARI/GP}}==
<lang parigp>reduce(f, v)={
my(t=v[1]);
for(i=2,#v,t=f(t,v[i]));
t
};
reduce((a,b)->a+b, [1,2,3,4,5,6,7,8,9,10])</lang>
 
{{works with|PARI/GP|2.8.1+}}
<lang parigp>fold((a,b)->a+b, [1..10])</lang>
 
=={{header|Pascal}}==
{{works with|Free Pascal}}
Should work with many pascal dialects
<lang pascal>program reduce;
 
type
// tmyArray = array of LongInt;
tmyArray = array[-5..5] of LongInt;
tmyFunc = function (a,b:LongInt):LongInt;
 
function add(x,y:LongInt):LongInt;
begin
add := x+y;
end;
 
function sub(k,l:LongInt):LongInt;
begin
sub := k-l;
end;
 
function mul(r,t:LongInt):LongInt;
begin
mul := r*t;
end;
 
function reduce(myFunc:tmyFunc;a:tmyArray):LongInt;
var
i,res : LongInt;
begin
res := a[low(a)];
For i := low(a)+1 to high(a) do
res := myFunc(res,a[i]);
reduce := res;
end;
 
procedure InitMyArray(var a:tmyArray);
var
i: LongInt;
begin
For i := low(a) to high(a) do
begin
//no a[i] = 0
a[i] := i + ord(i=0);
write(a[i],',');
end;
writeln(#8#32);
end;
 
var
ma : tmyArray;
BEGIN
InitMyArray(ma);
writeln(reduce(@add,ma));
writeln(reduce(@sub,ma));
writeln(reduce(@mul,ma));
END.</lang>
output
<pre>-5,-4,-3,-2,-1,1,1,2,3,4,5
1
-11
-1440</pre>
 
=={{header|Perl}}==
Perl's reduce function is in a standard package.
<lang perl>use List::Util 'reduce';
 
# note the use of the odd $a and $b globals
print +(reduce {$a + $b} 1 .. 10), "\n";
 
# first argument is really an anon function; you could also do this:
sub func { $b & 1 ? "$a $b" : "$b $a" }
print +(reduce \&func, 1 .. 10), "\n"</lang>
 
=={{header|Phix}}==
{{trans|C}}
<lang Phix>function add(integer a, integer b)
return a + b
end function
 
function sub(integer a, integer b)
return a - b
end function
 
function mul(integer a, integer b)
return a * b
end function
 
function reduce(integer rid, sequence s)
object res = s[1]
for i=2 to length(s) do
res = call_func(rid,{res,s[i]})
end for
return res
end function
 
?reduce(routine_id("add"),tagset(5))
?reduce(routine_id("sub"),tagset(5))
?reduce(routine_id("mul"),tagset(5))</lang>
{{out}}
<pre>
15
-13
120
</pre>
 
=={{header|Phixmonti}}==
<lang Phixmonti>include ..\Utilitys.pmt
 
def add + enddef
def sub - enddef
def mul * enddef
 
def reduce >ps
1 get
swap len 2 swap 2 tolist for
get rot swap tps exec swap
endfor
ps> drop
swap
enddef
 
 
( 1 2 3 4 5 )
getid add reduce ?
getid sub reduce ?
getid mul reduce ?</lang>
 
 
=={{header|PicoLisp}}==
<lang PicoLisp>(de reduce ("Fun" "Lst")
(let "A" (car "Lst")
(for "N" (cdr "Lst")
(setq "A" ("Fun" "A" "N")) )
"A" ) )
 
(println
(reduce + (1 2 3 4 5))
(reduce * (1 2 3 4 5)) )
(bye)</lang>
 
=={{header|PowerShell}}==
'Filter' is a more common sequence function in PowerShell than 'reduce' or 'map', but here is one way to accomplish 'reduce':
<lang PowerShell>
1..5 | ForEach-Object -Begin {$result = 0} -Process {$result += $_} -End {$result}
</lang>
{{Out}}
<pre>
15
</pre>
 
=={{header|Prolog}}==
 
===Using <code>foldl</code> from <code>library(apply)</code> and Lambda-Expressions from <code>library(lambda)</code>===
 
* SWI-Prolog's [https://www.swi-prolog.org/pldoc/man?section=apply library(apply)] provides a [https://www.swi-prolog.org/pldoc/doc_for?object=foldl/4 `foldl/4`] (the source code of which can be seen [https://www.swi-prolog.org/pldoc/doc/_SWI_/library/apply.pl?show=src#foldl/4 here]).
* '''Ulrich Neumerkel''' wrote `library(lambda)` which can be found [http://www.complang.tuwien.ac.at/ulrich/Prolog-inedit/lambda.pl here]. (However, SWI-Prolog's Lambda Expressions are by default based on Paulo Moura's [https://www.swi-prolog.org/search?for=yall library(yall)])
 
<lang Prolog>:- use_module(library(lambda)).
 
catamorphism :-
numlist(1,10,L),
foldl(\XS^YS^ZS^(ZS is XS+YS), L, 0, Sum),
format('Sum of ~w is ~w~n', [L, Sum]),
foldl(\XP^YP^ZP^(ZP is XP*YP), L, 1, Prod),
format('Prod of ~w is ~w~n', [L, Prod]),
string_to_list(LV, ""),
foldl(\XC^YC^ZC^(string_to_atom(XS, XC),string_concat(YC,XS,ZC)),
L, LV, Concat),
format('Concat of ~w is ~w~n', [L, Concat]).</lang>
{{out}}
<pre> ?- catamorphism.
Sum of [1,2,3,4,5,6,7,8,9,10] is 55
Prod of [1,2,3,4,5,6,7,8,9,10] is 3628800
Concat of [1,2,3,4,5,6,7,8,9,10] is 12345678910
true.
</pre>
 
===Bare Prolog===
 
This is based on SWI Prolog 8 and has the following specificities:
 
* The consbox functor is <code>[|]</code> instead of <code>.</code>
* The list is terminated by the special atomic thing <code>[]</code> (the empty list)
 
<lang Prolog>
% List to be folded:
%
% +---+---+---+---[] <-- list backbone/spine, composed of nodes, terminating in the empty list
% | | | |
% a b c d <-- list items/entries/elements/members
%
</lang>
 
====linear <code>foldl</code>====
 
<lang Prolog>
% Computes "Out" as:
%
% starter value -->--f-->--f-->--f-->--f-->-- Out
% | | | |
% a b c d
 
 
foldl(Foldy,[Item|Items],Acc,Result) :- % case of nonempty list
!, % GREEN CUT for determinism
call(Foldy,Item,Acc,AccNext), % call Foldy(Item,Acc,AccNext)
foldl(Foldy,Items,AccNext,Result). % then recurse (open to tail call optimization)
 
foldl(_,[],Acc,Result) :- % case of empty list
Acc=Result. % unification not in head for clarity
</lang>
 
====linear <code>foldr</code>====
 
<lang Prolog>
% Computes "Out" as:
%
% Out --<--f--<--f--<--f--<--f--<-- starter value
% | | | |
% a b c d
 
foldr(Foldy,[Item|Items],Starter,AccUp) :- % case of nonempty list
!, % GREEN CUT for determinism
foldr(Foldy,Items,Starter,AccUpPrev), % recurse (NOT open to tail-call optimization)
call(Foldy,Item,AccUpPrev,AccUp). % call Foldy(Item,AccupPrev,AccUp) as last action
 
foldr(_,[],Starter,AccUp) :- % empty list: bounce Starter "upwards" into AccUp
AccUp=Starter. % unification not in head for clarity
</lang>
 
====Unit tests====
 
This is written using SWI-Prolog's [https://www.swi-prolog.org/pldoc/doc_for?object=section(%27packages/plunit.html%27) unit testing framework].
 
Functions (in predicate form) of interest for our test cases:
 
<lang Prolog>
:- use_module(library(clpfd)). % We are using #= instead of the raw "is".
 
foldy_len(_Item,ThreadIn,ThreadOut) :-
succ(ThreadIn,ThreadOut).
 
foldy_add(Item,ThreadIn,ThreadOut) :-
ThreadOut #= Item+ThreadIn.
 
foldy_mult(Item,ThreadIn,ThreadOut) :-
ThreadOut #= Item*ThreadIn.
 
foldy_squadd(Item,ThreadIn,ThreadOut) :-
ThreadOut #= Item+(ThreadIn^2).
 
% '[|]' is SWI-Prolog specific, replace by '.' as consbox constructor in other Prologs
 
foldy_build(Item,ThreadIn,ThreadOut) :-
ThreadOut = '[|]'(Item,ThreadIn).
 
foldy_join(Item,ThreadIn,ThreadOut) :-
(ThreadIn \= "")
-> with_output_to(string(ThreadOut),format("~w,~w",[Item,ThreadIn]))
; with_output_to(string(ThreadOut),format("~w",[Item])).
 
% '=..' ("univ") constructs a term from a list of functor and arguments
 
foldy_expr(Functor,Item,ThreadIn,ThreadOut) :-
ThreadOut =.. [Functor,Item,ThreadIn].
</lang>
 
<lang Prolog>
:- begin_tests(foldr).
 
in([1,2,3,4,5]).
 
ffr(Foldy,List,Starter,AccUp) :- foldr(Foldy,List,Starter,AccUp).
 
test(foo_foldr_len) :- in(L),ffr(foldy_len , L , 0 , R), R=5.
test(foo_foldr_add) :- in(L),ffr(foldy_add , L , 0 , R), R=15.
test(foo_foldr_mult) :- in(L),ffr(foldy_mult , L , 1 , R), R=120.
test(foo_foldr_build) :- in(L),ffr(foldy_build , L , [] , R), R=[1,2,3,4,5].
test(foo_foldr_squadd) :- in(L),ffr(foldy_squadd , L , 0 , R), R=507425426245.
test(foo_foldr_join) :- in(L),ffr(foldy_join , L , "" , R), R="1,2,3,4,5".
test(foo_foldr_expr) :- in(L),ffr(foldy_expr(*) , L , 1 , R), R=1*(2*(3*(4*(5*1)))).
 
test(foo_foldr_len_empty) :- ffr(foldy_len , [], 0 , R), R=0.
test(foo_foldr_add_empty) :- ffr(foldy_add , [], 0 , R), R=0.
test(foo_foldr_mult_empty) :- ffr(foldy_mult , [], 1 , R), R=1.
test(foo_foldr_build_empty) :- ffr(foldy_build , [], [] , R), R=[].
test(foo_foldr_squadd_empty) :- ffr(foldy_squadd , [], 0 , R), R=0.
test(foo_foldr_join_empty) :- ffr(foldy_join , [], "" , R), R="".
test(foo_foldr_expr_empty) :- ffr(foldy_expr(*) , [], 1 , R), R=1.
 
% library(apply) has no "foldr" so no comparison tests!
 
:- end_tests(foldr).
 
 
:- begin_tests(foldl).
 
in([1,2,3,4,5]).
 
ffl(Foldy,List,Starter,Result) :- foldl(Foldy,List,Starter,Result).
 
test(foo_foldl_len) :- in(L),ffl(foldy_len , L , 0 , R), R=5.
test(foo_foldl_add) :- in(L),ffl(foldy_add , L, 0 , R), R=15.
test(foo_foldl_mult) :- in(L),ffl(foldy_mult , L, 1 , R), R=120.
test(foo_foldl_build) :- in(L),ffl(foldy_build , L, [] , R), R=[5,4,3,2,1].
test(foo_foldl_squadd) :- in(L),ffl(foldy_squadd , L, 0 , R), R=21909.
test(foo_foldl_join) :- in(L),ffl(foldy_join , L, "" , R), R="5,4,3,2,1".
test(foo_foldl_expr) :- in(L),ffl(foldy_expr(*) , L, 1 , R), R=5*(4*(3*(2*(1*1)))).
 
test(foo_foldl_len_empty) :- ffl(foldy_len , [], 0 , R), R=0.
test(foo_foldl_add_empty) :- ffl(foldy_add , [], 0 , R), R=0.
test(foo_foldl_mult_empty) :- ffl(foldy_mult , [], 1 , R), R=1.
test(foo_foldl_build_empty) :- ffl(foldy_build , [], [] , R), R=[].
test(foo_foldl_squadd_empty) :- ffl(foldy_squadd , [], 0 , R), R=0.
test(foo_foldl_join_empty) :- ffl(foldy_join , [], "" , R), R="".
test(foo_foldl_expr_empty) :- ffl(foldy_expr(*) , [], 1 , R), R=1.
 
:- end_tests(foldl).
 
rt :- run_tests(foldr),run_tests(foldl).
</lang>
 
=={{header|Python}}==
<lang python>>>> # Python 2.X
>>> from operator import add
>>> listoflists = [['the', 'cat'], ['sat', 'on'], ['the', 'mat']]
>>> help(reduce)
Help on built-in function reduce in module __builtin__:
 
reduce(...)
reduce(function, sequence[, initial]) -> value
Apply a function of two arguments cumulatively to the items of a sequence,
from left to right, so as to reduce the sequence to a single value.
For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
((((1+2)+3)+4)+5). If initial is present, it is placed before the items
of the sequence in the calculation, and serves as a default when the
sequence is empty.
 
>>> reduce(add, listoflists, [])
['the', 'cat', 'sat', 'on', 'the', 'mat']
>>> </lang>
===Additional example===
<lang python># Python 3.X
 
from functools import reduce
from operator import add, mul
 
nums = range(1,11)
 
summation = reduce(add, nums)
 
product = reduce(mul, nums)
 
concatenation = reduce(lambda a, b: str(a) + str(b), nums)
 
print(summation, product, concatenation)</lang>
 
=={{header|Quackery}}==
Among its many other uses, <code>witheach</code> can act like reduce. In the Quackery shell (REPL):
<lang quackery>/O> 0 ' [ 1 2 3 4 5 ] witheach +
... 1 ' [ 1 2 3 4 5 ] witheach *
...
 
Stack: 15 120</lang>
 
=={{header|R}}==
 
Sum the numbers in a vector:
 
<lang R>
Reduce('+', c(2,30,400,5000))
5432
</lang>
 
Put a 0 between each pair of numbers:
 
<lang R>
Reduce(function(a,b){c(a,0,b)}, c(2,3,4,5))
2 0 3 0 4 0 5
</lang>
 
Generate all prefixes of a string:
 
<lang R>
Reduce(paste0, unlist(strsplit("freedom", NULL)), accum=T)
"f" "fr" "fre" "free" "freed" "freedo" "freedom"
</lang>
 
Filter and map:
 
<lang R>
Reduce(function(x,acc){if (0==x%%3) c(x*x,acc) else acc}, 0:22,
init=c(), right=T)
0 9 36 81 144 225 324 441
</lang>
 
=={{header|Racket}}==
<lang racket>
#lang racket
(define (fold f xs init)
(if (empty? xs)
init
(f (first xs)
(fold f (rest xs) init))))
 
(fold + '(1 2 3) 0) ; the result is 6
</lang>
 
=={{header|Raku}}==
(formerly Perl 6)
{{works with|Rakudo|2018.03}}
Any associative infix operator, either built-in or user-defined, may be turned into a reduce operator by putting it into square brackets (known as "the reduce metaoperator") and using it as a list operator. The operations will work left-to-right or right-to-left automatically depending on the natural associativity of the base operator.
<lang perl6>my @list = 1..10;
say [+] @list;
say [*] @list;
say [~] @list;
say min @list;
say max @list;
say [lcm] @list;</lang>
{{out}}
<pre>55
3628800
12345678910
1
10
2520</pre>
In addition to the reduce metaoperator, a general higher-order function, <tt>reduce</tt>, can apply any appropriate function. Reproducing the above in this form, using the function names of those operators, we have:
<lang perl6>my @list = 1..10;
say reduce &infix:<+>, @list;
say reduce &infix:<*>, @list;
say reduce &infix:<~>, @list;
say reduce &infix:<min>, @list;
say reduce &infix:<max>, @list;
say reduce &infix:<lcm>, @list;</lang>
 
=={{header|REXX}}==
This REXX example is modeled after the Raku example &nbsp; (it is NOT a translation).
 
Also, a &nbsp; '''list''' &nbsp; and &nbsp; '''show''' &nbsp; function were added, although they
aren't a catamorphism, as they don't produce or reduce the values to a &nbsp; ''single'' &nbsp; value, but
are included here to help display the values in the list.
<lang rexx>/*REXX program demonstrates a method for catamorphism for some simple functions. */
@list= 1 2 3 4 5 6 7 8 9 10
say 'list:' fold(@list, "list")
say ' sum:' fold(@list, "+" )
say 'prod:' fold(@list, "*" )
say ' cat:' fold(@list, "||" )
say ' min:' fold(@list, "min" )
say ' max:' fold(@list, "max" )
say ' avg:' fold(@list, "avg" )
say ' GCD:' fold(@list, "GCD" )
say ' LCM:' fold(@list, "LCM" )
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
fold: procedure; parse arg z; arg ,f; z = space(z); BIFs= 'MIN MAX LCM GCD'
za= translate(z, f, ' '); zf= f"("translate(z, ',' , " ")')'
if f== '+' | f=="*" then interpret "return" za
if f== '||' then return space(z, 0)
if f== 'AVG' then interpret "return" fold(z, '+') "/" words(z)
if wordpos(f, BIFs)\==0 then interpret "return" zf
if f=='LIST' | f=="SHOW" then return z
return 'illegal function:' arg(2)
/*──────────────────────────────────────────────────────────────────────────────────────*/
GCD: procedure; $=; do j=1 for arg(); $= $ arg(j)
end /*j*/
parse var $ x z .; if x=0 then x= z /* [↑] build an arg list.*/
x= abs(x)
do k=2 to words($); y= abs( word($, k)); if y=0 then iterate
do until _=0; _= x // y; x= y; y= _
end /*until*/
end /*k*/
return x
/*──────────────────────────────────────────────────────────────────────────────────────*/
LCM: procedure; $=; do j=1 for arg(); $= $ arg(j)
end /*j*/
x= abs(word($, 1)) /* [↑] build an arg list.*/
do k=2 to words($); != abs(word($, k)); if !=0 then return 0
x= x*! / GCD(x, !) /*GCD does the heavy work*/
end /*k*/
return x</lang>
{{out|output|:}}
<pre>
list: 1 2 3 4 5 6 7 8 9 10
sum: 55
prod: 3628800
cat: 12345678910
min: 1
max: 10
avg: 5.5
GCD: 1
LCM: 2520
</pre>
 
=={{header|Ring}}==
<lang ring>
n = list(10)
for i = 1 to 10
n[i] = i
next
see " +: " + cat(10,"+") + nl+
" -: " + cat(10,"-") + nl +
" *: " + cat(10,"*") + nl +
" /: " + cat(10,"/") + nl+
" ^: " + cat(10,"^") + nl +
"min: " + cat(10,"min") + nl+
"max: " + cat(10,"max") + nl+
"avg: " + cat(10,"avg") + nl +
"cat: " + cat(10,"cat") + nl
func cat count,op
cat = n[1]
cat2 = ""
for i = 2 to count
switch op
on "+" cat += n[i]
on "-" cat -= n[i]
on "*" cat *= n[i]
on "/" cat /= n[i]
on "^" cat ^= n[i]
on "max" cat = max(cat,n[i])
on "min" cat = min(cat,n[i])
on "avg" cat += n[i]
on "cat" cat2 += string(n[i])
off
next
if op = "avg" cat = cat / count ok
if op = "cat" decimals(0) cat = string(n[1])+cat2 ok
return cat
</lang>
 
=={{header|Ruby}}==
The method inject (and it's alias reduce) can be used in several ways; the simplest is to give a methodname as argument:
<lang ruby># sum:
p (1..10).inject(:+)
# smallest number divisible by all numbers from 1 to 20:
p (1..20).inject(:lcm) #lcm: lowest common multiple
</lang>The most versatile way uses a accumulator object (memo) and a block. In this example Pascal's triangle is generated by using an array [1,1] and inserting the sum of each consecutive pair of numbers from the previous row.
<lang ruby>p row = [1]
10.times{p row = row.each_cons(2).inject([1,1]){|ar,(a,b)| ar.insert(-2, a+b)} }
 
# [1]
# [1, 1]
# [1, 2, 1]
# [1, 3, 3, 1]
# [1, 4, 6, 4, 1]
# [1, 5, 10, 10, 5, 1]
# [1, 6, 15, 20, 15, 6, 1]
# etc
</lang>
 
=={{header|Run BASIC}}==
<lang runbasic>for i = 1 to 10 :n(i) = i:next i
 
print " +: ";" ";cat(10,"+")
print " -: ";" ";cat(10,"-")
print " *: ";" ";cat(10,"*")
print " /: ";" ";cat(10,"/")
print " ^: ";" ";cat(10,"^")
print "min: ";" ";cat(10,"min")
print "max: ";" ";cat(10,"max")
print "avg: ";" ";cat(10,"avg")
print "cat: ";" ";cat(10,"cat")
 
function cat(count,op$)
cat = n(1)
for i = 2 to count
if op$ = "+" then cat = cat + n(i)
if op$ = "-" then cat = cat - n(i)
if op$ = "*" then cat = cat * n(i)
if op$ = "/" then cat = cat / n(i)
if op$ = "^" then cat = cat ^ n(i)
if op$ = "max" then cat = max(cat,n(i))
if op$ = "min" then cat = min(cat,n(i))
if op$ = "avg" then cat = cat + n(i)
if op$ = "cat" then cat$ = cat$ + str$(n(i))
next i
if op$ = "avg" then cat = cat / count
if op$ = "cat" then cat = val(str$(n(1))+cat$)
end function</lang>
<pre> +: 55
-: -53
*: 3628800
/: 2.75573205e-7
^: 1
min: 1
max: 10
avg: 5.5
cat: 12345678910</pre>
 
=={{header|Rust}}==
 
<lang rust>fn main() {
println!("Sum: {}", (1..10).fold(0, |acc, n| acc + n));
println!("Product: {}", (1..10).fold(1, |acc, n| acc * n));
let chars = ['a', 'b', 'c', 'd', 'e'];
println!("Concatenation: {}",
chars.iter().map(|&c| (c as u8 + 1) as char).collect::<String>());
}</lang>
 
{{out}}
<pre>
Sum: 45
Product: 362880
Concatenation: bcdef
</pre>
 
=={{header|Scala}}==
<lang scala>object Main extends App {
val a = Seq(1, 2, 3, 4, 5)
println(s"Array : ${a.mkString(", ")}")
println(s"Sum : ${a.sum}")
println(s"Difference : ${a.reduce { (x, y) => x - y }}")
println(s"Product : ${a.product}")
println(s"Minimum : ${a.min}")
println(s"Maximum : ${a.max}")
}</lang>
 
=={{header|Scheme}}==
===Implementation===
reduce implemented for a single list:
<lang scheme>(define (reduce fn init lst)
(do ((val init (fn (car rem) val)) ; accumulated value passed as second argument
(rem lst (cdr rem)))
((null? rem) val)))
 
(display (reduce + 0 '(1 2 3 4 5))) (newline) ; => 15
(display (reduce expt 2 '(3 4))) (newline) ; => 262144</lang>
===Using SRFI 1===
There is also an implementation of fold and fold-right in SRFI-1, for lists.
 
These take a two-argument procedure: (lambda (value acc) ...) where value is the next value in the list, and acc is the accumulated value. The initial value is used for the first value of acc.
 
<pre>
> (import (srfi 1))
> (fold + 0 '(1 2 3 4 5))
15
> (fold expt 2 '(3 4)) ; => (expt 4 (expt 3 2))
262144
> (fold-right expt 2 '(3 4)) ; => (expt 3 (expt 4 2))
43046721
</pre>
 
More than one list may be folded over, when the function is passed one item from each list plus the accumulated value:
 
<pre>
> (fold + 0 '(1 2 3) '(4 5 6)) ; add up all the numbers in all the lists
21
</pre>
 
=={{header|Sidef}}==
<lang ruby>say (1..10 -> reduce('+'));
say (1..10 -> reduce{|a,b| a + b});</lang>
 
=={{header|Standard ML}}==
<lang sml>- val nums = [1,2,3,4,5,6,7,8,9,10];
val nums = [1,2,3,4,5,6,7,8,9,10] : int list
- val sum = foldl op+ 0 nums;
val sum = 55 : int
- val product = foldl op* 1 nums;
val product = 3628800 : int</lang>
 
=={{header|Swift}}==
<lang swift>let nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
 
print(nums.reduce(0, +))
print(nums.reduce(1, *))
print(nums.reduce("", { $0 + String($1) }))</lang>
 
{{out}}
<pre>55
3628800
12345678910</pre>
 
=={{header|Tailspin}}==
It is probably easier to just write the whole thing as an inline transform rather than create a utility.
<lang tailspin>
[1..5] -> \(@: $(1); $(2..last)... -> @: $@ + $; $@!\) -> '$;
' -> !OUT::write
[1..5] -> \(@: $(1); $(2..last)... -> @: $@ - $; $@!\) -> '$;
' -> !OUT::write
[1..5] -> \(@: $(1); $(2..last)... -> @: $@ * $; $@!\) -> '$;
' -> !OUT::write
</lang>
{{out}}
<pre>
15
-13
120
</pre>
 
If you really want to make a utility, it could look like this:
<lang tailspin>
templates fold&{op:}
@: $(1);
$(2..last)... -> @: [$@, $] -> op;
$@ !
end fold
 
templates add
$(1) + $(2) !
end add
 
templates mul
$(1) * $(2) !
end mul
 
[1..5] -> fold&{op:add} -> '$;
' -> !OUT::write
 
[1..5] -> fold&{op:mul} -> '$;
' -> !OUT::write
</lang>
{{out}}
<pre>
15
120
</pre>
 
=={{header|Tcl}}==
Tcl does not come with a built-in <tt>fold</tt> command, but it is easy to construct:
<lang tcl>proc fold {lambda zero list} {
set accumulator $zero
foreach item $list {
set accumulator [apply $lambda $accumulator $item]
}
return $accumulator
}</lang>
Demonstrating:
<lang tcl>set 1to5 {1 2 3 4 5}
 
puts [fold {{a b} {expr {$a+$b}}} 0 $1to5]
puts [fold {{a b} {expr {$a*$b}}} 1 $1to5]
puts [fold {{a b} {return $a,$b}} x $1to5]</lang>
{{out}}
<pre>
15
120
x,1,2,3,4,5
</pre>
Note that these particular operations would more conventionally be written as:
<lang tcl>puts [::tcl::mathop::+ {*}$1to5]
puts [::tcl::mathop::* {*}$1to5]
puts x,[join $1to5 ,]</lang>
But those are not general catamorphisms.
 
=={{header|VBA}}==
<lang vb>Public Sub reduce()
s = [{1,2,3,4,5}]
Debug.Print WorksheetFunction.Sum(s)
Debug.Print WorksheetFunction.Product(s)
End Sub</lang>
 
=={{header|WDTE}}==
Translated from the JavaScript ES6 example with a few modifications.
 
<lang WDTE>let a => import 'arrays';
let s => import 'stream';
let str => import 'strings';
 
# Sum of [1, 10]:
let nums => [1; 2; 3; 4; 5; 6; 7; 8; 9; 10];
a.stream nums -> s.reduce 0 + -- io.writeln io.stdout;
 
# As an alternative to an array, a range stream can be used. Here's the product of [1, 11):
s.range 1 11 -> s.reduce 1 * -- io.writeln io.stdout;
 
# And here's a concatenation:
s.range 1 11 -> s.reduce '' (str.format '{}{}') -- io.writeln io.stdout;</lang>
 
=={{header|Wortel}}==
You can reduce an array with the <code>!/</code> operator.
<lang wortel>!/ ^+ [1 2 3] ; returns 6</lang>
If you want to reduce with an initial value, you'll need the <code>@fold</code> operator.
<lang wortel>@fold ^+ 1 [1 2 3] ; returns 7</lang>
 
{{out}}
<pre>55
3628800
12345678910</pre>
 
=={{header|Wren}}==
<lang ecmascript>var a = [1, 2, 3, 4, 5]
var sum = a.reduce { |acc, i| acc + i }
var prod = a.reduce { |acc, i| acc * i }
var sumSq = a.reduce { |acc, i| acc + i*i }
System.print(a)
System.print("Sum is %(sum)")
System.print("Product is %(prod)")
System.print("Sum of squares is %(sumSq)")</lang>
 
{{out}}
<pre>
[1, 2, 3, 4, 5]
Sum is 15
Product is 120
Sum of squares is 55
</pre>
 
=={{header|zkl}}==
Most sequence objects in zkl have a reduce method.
<lang zkl>T("foo","bar").reduce(fcn(p,n){p+n}) //--> "foobar"
"123four5".reduce(fcn(p,c){p+(c.matches("[0-9]") and c or 0)}, 0) //-->11
File("foo.zkl").reduce('+(1).fpM("0-"),0) //->5 (lines in file)</lang>
 
=={{header|ZX Spectrum Basic}}==
<pre>10
{{trans|BBC_BASIC}}
24</pre>
<lang zxbasic>10 DIM a(5)
20 FOR i=1 TO 5
30 READ a(i)
40 NEXT i
50 DATA 1,2,3,4,5
60 LET o$="+": GO SUB 1000: PRINT tmp
70 LET o$="-": GO SUB 1000: PRINT tmp
80 LET o$="*": GO SUB 1000: PRINT tmp
90 STOP
1000 REM Reduce
1010 LET tmp=a(1)
1020 FOR i=2 TO 5
1030 LET tmp=VAL ("tmp"+o$+"a(i)")
1040 NEXT i
1050 RETURN </lang>
Drkameleon
1,532

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