ppop ( seq -- seq' )
Persistent sequence protocol

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ppush ( val seq -- seq' )

Vocabulary
persistent.sequences

Inputs

seq	a sequence

Outputs

seq'	a sequence

Generic word contract
Persistent analogue of pop*. Outputs a new sequence with all elements of seq except for the final element.

Definition

IN: persistent.sequences

GENERIC: ppop ( seq -- seq' )

Methods

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

M: persistent-vector ppop
    dup count>> {
        { 0 [ empty-error ] }
        { 1 [ drop PV{ } ] }
        [
            [
                clone dup tail>> children>> length 1 >
                [ ppop-tail ] [ ppop-new-tail ] if
            ] dip 1 - >>count
        ]
    } case ;


USING: persistent.sequences sequences ;

M: sequence ppop but-last ;


USING: accessors kernel math persistent.sequences sequences
vlists ;

M: vlist ppop
    [ empty-vlist-error ]
    [ [ length>> 1 - ] [ vector>> ] bi vlist boa ] if-empty ;