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(SRFI-1 Deleting): Rewrite delete and

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delete-duplicates, adding behaviour details specified by srfi-1.
This commit is contained in:
Kevin Ryde 2003-05-15 23:35:32 +00:00
parent 26e6879536
commit b6b9376ae0
1 changed files with 34 additions and 15 deletions
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49
doc/ref/srfi-modules.texi
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@ -690,29 +690,48 @@ Equality is determined by the equality predicate @var{=}, or
@c FIXME::martin: Review me!
The procedures for deleting elements from a list either accept a
predicate or a comparison object for determining which elements are to
be removed.
@deffn {Scheme Procedure} delete x lst [=]
@deffnx {Scheme Procedure} delete! x lst [=]
Return a list containing all elements from @var{lst}, but without the
elements equal to @var{x}. Equality is determined by the equality
predicate @var{=}, which defaults to @code{equal?} if not given.
Return a list containing the elements of @var{lst} but with those
equal to @var{x} deleted. The returned elements will be in the same
order as they were in @var{lst}.
@code{delete!} is allowed, but not required to modify the structure of
the argument list in order to produce the result.
Equality is determined by the @var{=} predicate, or @code{equal?} if
not given. An equality call is made just once for each element, but
the order in which the calls are made on the elements is unspecified.
The equality calls are always @code{(= x elem)}, ie. the given @var{x}
is first. This means for instance elements greater than 5 can be
deleted with @code{(delete 5 lst <)}.
@code{delete} does not modify @var{lst}, but the return might share a
common tail with @var{lst}. @code{delete!} may modify the structure
of @var{lst} to construct its return.
@end deffn
@deffn {Scheme Procedure} delete-duplicates lst [=]
@deffnx {Scheme Procedure} delete-duplicates! lst [=]
Return a list containing all elements from @var{lst}, but without
duplicate elements. Equality of elements is determined by the
equality predicate @var{=}, which defaults to @code{equal?} if not
given.
Return a list containing the elements of @var{lst} but without
duplicates.
@code{delete-duplicates!} is allowed, but not required to modify the
structure of the argument list in order to produce the result.
When elements are equal, only the first in @var{lst} is retained.
Equal elements can be anywhere in @var{lst}, they don't have to be
adjacent. The returned list will have the retained elements in the
same order as they were in @var{lst}.
Equality is determined by the @var{=} predicate, or @code{equal?} if
not given. Calls @code{(= x y)} are made with element @var{x} being
before @var{y} in @var{lst}. A call is made at most once for each
combination, but the sequence of the calls across the elements is
unspecified.
@code{delete-duplicates} does not modify @var{lst}, but the return
might share a common tail with @var{lst}. @code{delete-duplicates!}
may modify the structure of @var{lst} to construct its return.
In the worst case, this is an @math{O(N^2)} algorithm because it must
check each element against all those preceding it. For long lists it
is more efficient to sort and then compare only adjacent elements.
@end deffn