(use callable-alists callable-hash-tables)

(define a (make-callable-alist '()))
(set! (a 'foo) 42)
(print "foo (alist) = " (a 'foo))

(define ht (make-callable-hash-table '()))
(set! (ht 'foo) 42)
(print "foo (hash table) = " (ht 'foo))