Re: Ada vs. LISP

[gateley@m2.csc.ti.com (John Gateley)]

In article <45978@linus.UUCP> eachus@mbunix (Robert I. Eachus) writes:
>     One of the things which I did during the ANSI standardization of
>Ada was to look for ANYTHING in the standard which would make
>translation of LISP programs into Ada difficult.

Hmmm.... how would the following programs be written in Ada:
(I give both Scheme and CL versions, take your pick)

Scheme                           CL
(define x                        (defun x (n)
  (lambda (n)                      (function (lambda (m)
    (lambda (m)                       (+ n m)))
      (+ m n))))

that is, how can you write first class functions? These are quite
useful for things like writing an interpreter for Lisp in Lisp, or
a denotational semantics, or table abstractions where the elements are
functions etc.

Scheme                           CL
(define print                    (defun print (x)
  (lambda (x)                      (typecase x
    (cond                            (integer 1)
      ((integer? x) 1)               (real 2)
      ((real? x) 2)                  (complex 3)
      ((complex? x) 3)               (vector 4)))
      ((vector? x) 4))))

that is, how can you write dynamically typed functions?

I do not think you can.
These two features of Lisp that I have highlighted are fundamental aspects
of the langauge. That is, it is not fair to say that you can translate
programs from Lisp to Ada unless you can handle these cases as well.
I am assuming that you do not mean you can write a Lisp compiler in Ada
(since you can do that in any language), but that you can translate
any expression in Lisp into a corresponding Ada fragment.

John
gateley@tilde.csc.ti.com