factor/library/cons.factor

! :folding=indent:collapseFolds=1:

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! Copyright (C) 2003, 2004 Slava Pestov.
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IN: lists USE: kernel USE: stack

: swons ( cdr car -- [ car | cdr ] )
    #! Push a new cons cell. If the cdr is f or a proper list,
    #! has the effect of prepending the car to the cdr.
    swap cons ; inline

: uncons ( [ car | cdr ] -- car cdr )
    #! Push both the head and tail of a list.
    dup car swap cdr ; inline

: unit ( a -- [ a ] )
    #! Construct a proper list of one element.
    f cons ; inline

: unswons ( [ car | cdr ] -- cdr car )
    #! Push both the head and tail of a list.
    dup cdr swap car ; inline

: 2car ( cons cons -- car car )
    swap car swap car ;

: 2cdr ( cons cons -- car car )
    swap cdr swap cdr ;

: 2cons ( cdr1 cdr2 car1 car2 -- cons1 cons2 )
    rot swons >r cons r> ;

: 2swons ( cdr1 cdr2 car1 car2 -- cons1 cons2 )
    rot cons >r swons r> ;