Vocabulary
persistent.sequences

Inputs and outputs

val	an object
i	an integer
seq	a sequence
seq'	a sequence

Generic word contract
Persistent analogue of set-nth. Outputs a new sequence with the ith element replaced by val.

Definition

IN: persistent.sequences

GENERIC: new-nth ( val i seq -- seq' )

Methods

USING: accessors kernel math persistent.sequences
persistent.vectors ;

M: persistent-vector new-nth
2dup count>> =
[ nip ppush ] [
clone 2dup tail-offset >=
[ [ node-mask ] dip [ node-set-nth ] change-tail ]
[ [ (new-nth) ] change-root ] if
] if ;

USING: kernel persistent.sequences sequences ;

M: sequence new-nth clone [ set-nth ] keep ;