I'm writing an implementation of SRFI-1 in Javascript (just for fun) and I
have a question about SRFI-1's any procedure. In the docs it says that
"(any) does not return a simple boolean (#t or #f), but a general value",
however it also says that any must be called with a "procedure taking n
arguments and returning a boolean result".
I've been testing my implementation against Chicken for correctness and
here's what I get on Chicken:
#;2> (any (lambda (x) (if (even? x) x)) '(1 2 3))
#;3> (any (lambda (x) (even? x)) '(1 2 3))
#t
#;4> (any even? '(1 3 5))
#f
For #3 and #4 any correctly returns #t and #f respectively. However for #2
shouldn't any return 2 instead of, what I'm assuming is, (void)? What is
the correct behavior here?
>From SRFI-1:
any pred clist1 clist2 ... -> value
Applies the predicate across the lists, returning true if the predicate
returns true on any application.
If there are n list arguments clist1 ... clistn, then *pred must be a
procedure taking n arguments and returning a boolean result*.
any applies pred to the first elements of the clisti parameters. If this
application returns a true value, any immediately returns that value.
Otherwise, it iterates, applying pred to the second elements of the clisti
parameters, then the third, and so forth. The iteration stops when a true
value is produced or one of the lists runs out of values; in the latter
case, any returns #f. The application of pred to the last element of the
lists is a tail call.
Note the difference between find and any -- find returns the element that
satisfied the predicate; *any returns the true value that the predicate
produced*.
*Like every, any's name does not end with a question mark -- this is to
indicate that it does not return a simple boolean (#t or #f), but a general
value.*
(any integer? '(a 3 b 2.7)) => #t
(any integer? '(a 3.1 b 2.7)) => #f
(any < '(3 1 4 1 5)
'(2 7 1 8 2)) => #t
--
Nick Zarczynski
Rent a Geek IT Services <http://rentageekit.com>
Blog 4 <http://nickzarr.com>
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