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(slib.info)Lists as sets

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Lists as sets
.............

  `eqv?' is used to test for membership by procedures which treat lists
as sets.

 - Function: adjoin e l
     `adjoin' returns the adjoint of the element E and the list L.
     That is, if E is in L, `adjoin' returns L, otherwise, it returns
     `(cons E L)'.

     Example:
          (adjoin 'baz '(bar baz bang))
             => (bar baz bang)
          (adjoin 'foo '(bar baz bang))
             => (foo bar baz bang)

 - Function: union l1 l2
     `union' returns the combination of L1 and L2.  Duplicates between
     L1 and L2 are culled.  Duplicates within L1 or within L2 may or
     may not be removed.

     Example:
          (union '(1 2 3 4) '(5 6 7 8))
             => (8 7 6 5 1 2 3 4)
          (union '(1 2 3 4) '(3 4 5 6))
             => (6 5 1 2 3 4)

 - Function: intersection l1 l2
     `intersection' returns all elements that are in both L1 and L2.

     Example:
          (intersection '(1 2 3 4) '(3 4 5 6))
             => (3 4)
          (intersection '(1 2 3 4) '(5 6 7 8))
             => ()

 - Function: set-difference l1 l2
     `set-difference' returns all elements that are in L1 but not in L2.

     Example:
          (set-difference '(1 2 3 4) '(3 4 5 6))
             => (1 2)
          (set-difference '(1 2 3 4) '(1 2 3 4 5 6))
             => ()

 - Function: member-if pred lst
     `member-if' returns LST if `(PRED ELEMENT)' is `#t' for any
     ELEMENT in LST.  Returns `#f' if PRED does not apply to any
     ELEMENT in LST.

     Example:
          (member-if vector? '(1 2 3 4))
             => #f
          (member-if number? '(1 2 3 4))
             => (1 2 3 4)

 - Function: some pred lst1 lst2 ...
     PRED is a boolean function of as many arguments as there are list
     arguments to `some' i.e., LST plus any optional arguments.  PRED
     is applied to successive elements of the list arguments in order.
     `some' returns `#t' as soon as one of these applications returns
     `#t', and is `#f' if none returns `#t'.  All the lists should have
     the same length.

     Example:
          (some odd? '(1 2 3 4))
             => #t
          
          (some odd? '(2 4 6 8))
             => #f
          
          (some > '(2 3) '(1 4))
             => #f

 - Function: every pred lst1 lst2 ...
     `every' is analogous to `some' except it returns `#t' if every
     application of PRED is `#t' and `#f' otherwise.

     Example:
          (every even? '(1 2 3 4))
             => #f
          
          (every even? '(2 4 6 8))
             => #t
          
          (every > '(2 3) '(1 4))
             => #f

 - Function: notany pred lst1 ...
     `notany' is analogous to `some' but returns `#t' if no application
     of PRED returns `#t' or `#f' as soon as any one does.

 - Function: notevery pred lst1 ...
     `notevery' is analogous to `some' but returns `#t' as soon as an
     application of PRED returns `#f', and `#f' otherwise.

     Example:
          (notevery even? '(1 2 3 4))
             => #t
          
          (notevery even? '(2 4 6 8))
             => #f

 - Function: list-of?? predicate
     Returns a predicate which returns true if its argument is a list
     every element of which satisfies PREDICATE.

 - Function: list-of?? predicate low-bound high-bound
     LOW-BOUND and HIGH-BOUND are non-negative integers.  `list-of??'
     returns a predicate which returns true if its argument is a list
     of length between LOW-BOUND and HIGH-BOUND (inclusive); every
     element of which satisfies PREDICATE.

 - Function: list-of?? predicate bound
     BOUND is an integer.  If BOUND is negative, `list-of??' returns a
     predicate which returns true if its argument is a list of length
     greater than `(- BOUND)'; every element of which satisfies
     PREDICATE.  Otherwise, `list-of??'  returns a predicate which
     returns true if its argument is a list of length less than or
     equal to BOUND; every element of which satisfies PREDICATE.

 - Function: find-if pred lst
     `find-if' searches for the first ELEMENT in LST such that `(PRED
     ELEMENT)' returns `#t'.  If it finds any such ELEMENT in LST,
     ELEMENT is returned.  Otherwise, `#f' is returned.

     Example:
          (find-if number? '(foo 1 bar 2))
             => 1
          
          (find-if number? '(foo bar baz bang))
             => #f
          
          (find-if symbol? '(1 2 foo bar))
             => foo

 - Function: remove elt lst
     `remove' removes all occurrences of ELT from LST using `eqv?' to
     test for equality and returns everything that's left.  N.B.: other
     implementations (Chez, Scheme->C and T, at least) use `equal?' as
     the equality test.

     Example:
          (remove 1 '(1 2 1 3 1 4 1 5))
             => (2 3 4 5)
          
          (remove 'foo '(bar baz bang))
             => (bar baz bang)

 - Function: remove-if pred lst
     `remove-if' removes all ELEMENTs from LST where `(PRED ELEMENT)'
     is `#t' and returns everything that's left.

     Example:
          (remove-if number? '(1 2 3 4))
             => ()
          
          (remove-if even? '(1 2 3 4 5 6 7 8))
             => (1 3 5 7)

 - Function: remove-if-not pred lst
     `remove-if-not' removes all ELEMENTs from LST for which `(PRED
     ELEMENT)' is `#f' and returns everything that's left.

     Example:
          (remove-if-not number? '(foo bar baz))
             => ()
          (remove-if-not odd? '(1 2 3 4 5 6 7 8))
             => (1 3 5 7)

 - Function: has-duplicates? lst
     returns `#t' if 2 members of LST are `equal?', `#f' otherwise.

     Example:
          (has-duplicates? '(1 2 3 4))
             => #f
          
          (has-duplicates? '(2 4 3 4))
             => #t

  The procedure `remove-duplicates' uses `member' (rather than `memv').

 - Function: remove-duplicates lst
     returns a copy of LST with its duplicate members removed.
     Elements are considered duplicate if they are `equal?'.

     Example:
          (remove-duplicates '(1 2 3 4))
             => (1 2 3 4)
          
          (remove-duplicates '(2 4 3 4))
             => (2 4 3)