! :folding=indent:collapseFolds=1:

! $Id$
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! Copyright (C) 2004 Slava Pestov.
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IN: lists
USE: logic
USE: combinators
USE: kernel
USE: stack

: assoc? ( list -- ? )
    #! Push if the list appears to be an alist (each element is
    #! a cons).
    dup list? [ [ cons? ] all? ] [ drop f ] ifte ;

: assoc* ( key alist -- [ key | value ] )
    #! Looks up the key in an alist. Push the key/value pair.
    #! Most of the time you want to use assoc not assoc*.
    dup [
        2dup car car = [
            nip car
        ] [
            cdr assoc*
        ] ifte
    ] [
        2drop f
    ] ifte ;

: assoc ( key alist -- value )
    #! Looks up the key in an alist. An alist is a proper list
    #! of comma pairs, the car of each pair is a key, the cdr is
    #! the value. For example:
    #! [ [ 1 | "one" ] [ 2 | "two" ] [ 3 | "three" ] ]
    assoc* dup [ cdr ] when ;

: set-assoc ( value key alist -- alist )
    #! Sets the key in the alist. Does not modify the existing
    #! list by consing a new key/value pair onto the alist. The
    #! newly-added pair 'shadows' the previous value.
    >r swons r> [ dupd car= not ] subset cons ;