Ol provides out-of-the-box key-value dictionaries called "finite functions". Such name means that you can use these dictionaries as regular functions along with using them as a dictionary.
The finite functions (ffs) are internally represented as red-black trees, so performance is much better than commonly used associative lists.
> (define numbers {
1 "one"
7 "seven"
3 "three" })
> numbers
#ff((1 . "one") (3 . "three") (7 . "seven"))
> (numbers 1)
"one"
; the optional second argument will be returned if the key is not found
> (numbers 7 #f)
"seven"
> (numbers 33 "unknown")
"unknown"As a key you should use objects that are comparable in sense of eq?. Such as
- symbols,
- #true, #false, #null, #empty, #eof
- small numbers (in sense of
value?),- -16777215 .. +16777215 for 32-bit machines
- -72057594037927935 .. +72057594037927935 for 64-bit machines.
in fact, you can use any object as a key, but you must remember that
({ "me" 111} "me")will fail while(let ((me "me")) ({ me 111} me))will ok.
The value #empty (#e, and empty which is deprecated) is an empty finite function. It contains no mappings.
get, getf, put, put!, del, keys, make-ff, list->ff, ff->list, alist->ff, ff->alist, pairs->ff, ff->pairs, ff-for-each, ff-map, ff-fold, ff-foldr, ff-diff, ff-union, ff-replace
(get ff key default), procedure
Wrapper for direct ff call. Returns the default value if ff is not ff, instead of a runtime error.
> (define numbers {
1 "one"
7 "seven"
3 "three" })
> (get numbers 1 "not found")
"one"
> (get numbers 77 "not found")
"not found"
> (get 'not-an-ff 1 "not found")
"not found"(getf ff key), procedure
Alias for (get ff key #false).
(put ff key value), procedure
Returns a (possibly rebalanced) copy of ff with added new key-value pair.
> (put #empty 7 42)
#ff((7 . 42))
> (put {1 2 3 "4"} 7 'itsme)
#ff((1 . 2) (3 . "4") (7 . itsme))(put! ff key value), procedure
This is a non-functional feature. Use them only if you know what you are doing! This can lead to unexpected behavior of your program.
Modifies existing ff by changing value of an existing key-value pair to new value.
(del ff key), procedure
(keys ff), procedure
> (keys { 1 "one"
7 "seven"
3 "three" })
'(1 3 7)(make-ff list), procedure
Same as list->ff.
(list->ff list), procedure
> (list->ff '())
#ff()
> (list->ff '(1 2 3 4))
#ff((1 . 2) (3 . 4))
> (list->ff '(1 2 3 4 1 8))
#ff((1 . 8) (3 . 4))(ff->list ff), procedure
(alist->ff alist), procedure
> (alist->ff '())
#ff()
> (alist->ff '((1 . 2) (3 . 4)))
#ff((1 . 2) (3 . 4))
> (alist->ff '((1 . 2) (3 . 4) (1 . 8)))
#ff((1 . 8) (3 . 4))(pairs->ff pairs), procedure
Same as alist->ff.
(ff->pairs ff), procedure
Same as ff->alist.