# [plt-scheme] Re: Should PLT Scheme have two R6RS namespaces?

On Mar 23, 5:50 pm, Matthias Felleisen <matth... at ccs.neu.edu> wrote:
>* Units sounds like the exact proper design choice here.
*>*
*
Is there a way to specify that a signature conatains a certain syntax
definitions? The problem I can see is with lambda (eg. the following
code from srfi/1/search.ss):
(define (span pred lis)
(check-arg procedure? pred 'span)
(let recur ((lis lis))
(if (null-list? lis) (values '() '())
(let ((x (car lis)))
(if (pred x)
(let-values ([(prefix suffix) (recur (cdr lis))])
(values (cons x prefix) suffix))
(values '() lis))))))
[...]
(define (any pred lis1 . lists)
(check-arg procedure? pred 'any)
(if (pair? lists)
;; N-ary case
(let-values ([(heads tails) (%cars+cdrs (cons lis1 lists))])
(and (pair? heads)
(let lp ((heads heads) (tails tails))
(let-values ([(next-heads next-tails) (%cars+cdrs
tails)])
(if (pair? next-heads)
(or (apply pred heads) (lp next-heads next-tails))
(apply pred heads)))))) ; Last PRED app is tail call.
;; Fast path
(and (not (null-list? lis1))
(let lp ((head (car lis1)) (tail (cdr lis1)))
(if (null-list? tail)
(pred head) ; Last PRED app is tail call.
(or (pred head) (lp (car tail) (cdr tail))))))))
note that cons is used to create a return value for the target
language in the first procedure, and to cons rest-lists in the host
language in the second procedure.