diff options
Diffstat (limited to 'module/srfi/srfi-1.scm')
-rw-r--r-- | module/srfi/srfi-1.scm | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/module/srfi/srfi-1.scm b/module/srfi/srfi-1.scm index 49ee46e40..01413c963 100644 --- a/module/srfi/srfi-1.scm +++ b/module/srfi/srfi-1.scm @@ -1350,6 +1350,30 @@ given REST parameters." (check-arg procedure? = lset-intersection!) (apply lset-intersection = list1 rest)) ; XXX:optimize +(define (lset-difference! = lset . removals) + "Return @var{lst} with any elements in the lists in @var{removals} +removed (ie.@: subtracted). For only one @var{lst} argument, just that +list is returned. + +The given @var{equal} procedure is used for comparing elements, called +as @code{(@var{equal} elem1 elemN)}. The first argument is from +@var{lst} and the second from one of the subsequent lists. But exactly +which calls are made and in what order is unspecified. + +@example +(lset-difference! eqv? (list 'x 'y)) @result{} (x y) +(lset-difference! eqv? (list 1 2 3) '(3 1)) @result{} (2) +(lset-difference! eqv? (list 1 2 3) '(3) '(2)) @result{} (1) +@end example + +@code{lset-difference!} may modify @var{lst} to form its result." + (check-arg procedure? = lset-intersection!) + (cond + ((null? lset) lset) + ((null? removals) lset) + (else (remove! (lambda (x) (any (lambda (s) (member x s =)) removals)) + lset)))) + (define (lset-xor! = . rest) (check-arg procedure? = lset-xor!) (apply lset-xor = rest)) ; XXX:optimize |