accumulate ( ... seq identity quot: ( ... prev elt -- ... next ) -- ... final newseq )
Factor handbook » The language » Collections » Sequence operations » Sequence combinators

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Vocabulary
sequences

Inputs

seq	a sequence
identity	an object
quot	a quotation with stack effect ( ... prev elt -- ... next )

Outputs

final	the final result
newseq	a new sequence

Word description
Combines successive elements of the sequence using a binary operation, and outputs a sequence of intermediate results, together with the final result.

The first element of the output sequence is identity. Then, on the first iteration, the two inputs to the quotation are identity and the first element of the input sequence. On successive iterations, the first input is the result of the previous iteration, and the second input is the next element of the input sequence.

When given the empty sequence, outputs a new empty sequence together with the identity.

Examples

USING: math prettyprint sequences ; { 2 2 2 2 2 } 0 [ + ] accumulate . .
{ 0 2 4 6 8 } 10

Notes
May be named scan or prefix sum in other languages.

See also
accumulate!, accumulate-as, accumulate*, accumulate*!, accumulate*-as

Definition

USING: kernel ;

IN: sequences

: accumulate
    ( ... seq identity quot: ( ... prev elt -- ... next ) -- ... final newseq )
    pick accumulate-as ; inline