Re: call/cc and proper tail recursion

[William Clinger <will@skinner.cs.uoregon.edu>]

    I will probably solve the problem for SCM by creating hidden
    expression types for CALL-WITH-CURRENT-CONTINUATION, EVAL, and APPLY
    which are called by interpreted procedures.

Perfectly reasonable.

    This is no problem for the first 2, but handling APPLY will cause
    substantial duplication of code since I need a subr APPLY as well.

I don't think I understand this.  Suppose %apply is the keyword of a
hidden special form that handles the restricted case of two-argument
apply.  Then the general apply can be written as a procedure via

    (define (apply f . args&arglist)
      (define (list* restlist)
        (cond ((null? restlist)
               (error "Too few arguments to apply"))
              ((null? (cdr restlist))
               (car restlist))
              (else (cons (car restlist)
                          (list* (cdr restlist))))))
      (%apply f (list* args&arglist)))

I know this is a little inefficient, but I don't see any substantial
duplication of code.  Perhaps I don't understand what a subr is.

Will