[r6rs-discuss] On the arity of comparators

[Ray Dillinger]

ISTR that several lisp dialects have had comparators that accept 
zero or more arguments. In those cases the 0 and 1 argument cases 
of comparators have, IIRC, been considered TRUE. 

It has to do with a recursive implementation where the zero-argument
or single-argument case is the base case. 


;; be wary of bugs in this code; I am typing it from memory 
;; and have not tested it. 
(define gencomp? (lambda (paircomp?)
    (define comp? (lambda  arglist
        (cond ((empty-list? arglist) #t)
              ((empty-list? (cdr arglist) #t)
              ((paircomp? (car arglist) (cadr arglist)) 
               (comp? (cdr arglist)))
              (else #f))))))

allows definition of all general comparisons as a function of the 
corresponding pairwise comparisons.  I remember being somewhat 
surprised when I saw the arity requirements in R4RS. 

				Bear