Hi,
I have to validate symbol-lists in various ways. For example if it must
contain exactly two values (in arbitrary order) I can do
(and (= (length mylist) 2)(memq 'val-a mylist) (memq 'val-b mylist))
To test if only certain values are allowed (but may be there multiple
times):
(every (lambda (elt) (memq elt '(val-a val-b))) mylist)
Now I have a case where one value must be present once and another value
at least once, so '(a b b) is valid as well as '(a b) but '(a a b) is
invalid.
I can use (filter) and check if the resulting list has exactly one
element, but is there a "native" function to either check if an element
is in a list exactly once?
Thanks
Urs
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