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

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Vocabulary
sequences

Inputs

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

Outputs

seq	a mutable sequence
final	the final result

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

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

When given the empty sequence, outputs the same empty sequence together with the identity.

Errors
Throws an error if the sequence is immutable, or the sequence cannot hold elements of the type output by quot.

Side effects
Modifies seq

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: sequences.private ;

IN: sequences

: accumulate!
    ( ... seq identity quot: ( ... prev elt -- ... next ) -- ... final seq )
    (accumulate) map! ; inline