Paste: amb and bag-of

USING: arrays continuations kernel namespaces sequences ;

IN: amb

<PRIVATE

SYMBOL: amb-failure

PRIVATE>
        
: amb ( sequence -- elt )
    [
	swap [ [ amb-failure set continue-with ] callcc0 2drop ] curry
	amb-failure get [ each ] dip
        continue
    ] curry callcc1 ;

: amb-init ( -- )
    [ amb-failure set t ] callcc1
    [ amb-init "amb: no more alternatives" throw ] unless ;

: amb-fail ( -- ) amb-failure get continue ;

: bag-of ( quot -- seq )
    { } clone
    [
	[ swap push amb-fail ] curry compose
	[ ] 2array amb call
    ] keep ;