---
name: "Array.fold"
section: "3kaya"
platform: "linux"
package: "kaya"
version: "0.4.4-6.2"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/Array.fold"
---

# Array.fold(3kaya)

Fold an array.

## NAME

Array::fold - Fold an array.

## SYNOPSIS

**b fold(** *b(a, b) f, \[a\] xs, b acc* **)**

## ARGUMENTS

**f** The function to use

**xs** The array

**acc** The initial value for folding.

## DESCRIPTION

Applies a function across an array. For example, given a function **sum**  which adds two integers:

-

   total = fold(sum,\[1,2,3,4,5\],0);\
    putStrLn(String(total));

This prints the sum of the values in the array **\[1,2,3,4,5\]** \
  The following example uses **fold**  to calculate the final direction.

-

   data Direction = North \| East \| South \| West;\
    data Turn = Left \| Right;\
    Direction doTurn(Turn turn, Direction current) {\
        case turn of {\
            Left -\> case current of {\
                North -\> new = West;\
                \| West -\> new = South;\
                \| South -\> new = East;\
                \| East -\> new = North;\
            }\
            \| Right -\> case current of {\
                North -\> new = East;\
                \| West -\> new = North;\
                \| South -\> new = West;\
                \| East -\> new = South;\
            } \
        }\
        return new;\
    }

   Void main() {\
        turns = \[Left,Left,Left,Right,Right,Left,Right,Left,Left\];\
        original = West;\
        final = fold(doTurn,turns,original);\
        // final = North\
    }

## AUTHORS

Kaya standard library by Edwin Brady, Chris Morris and others (kaya@kayalang.org). For further information see http://kayalang.org/

## LICENSE

The Kaya standard library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License (version 2.1 or any later version) as published by the Free Software Foundation.

## RELATED

**Array.map (3kaya)**