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From: mcdonald@uxe.cso.uiuc.edu
Newsgroups: comp.lang.ada
Subject: Re: Ada vs LISP vs C vs ...
Message-ID: <49700002@uxe.cso.uiuc.edu>
Date: 17 Mar 89 23:05:00 GMT
References: <8903161704.AA05024@ti.com>
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Nf-From: uxe.cso.uiuc.edu!mcdonald    Mar 17 17:05:00 1989
List-Id: <comp.lang.ada>


>The first thing we must do is agree on the definition of the term "general
>purpose language."  Opinions will vary, but in general the characteristics of
>such a language are that it can 1.)  add, subtract, multiply, and divide.
>2.) store the results of the above operations.  3.)  Branch to one of two
>different program paths based on the results of the above operations.
>Anything else is gravy, including bitwise logical operations (some of which
>are *damn* hard in Ada!)  The outcome of this is, technically, you can do
>anything in any "general purpose" language, and you can do it without writing
>a compiler or interpretter for some other language.  

I would like to propose one thing that a "general purpose" language
should allow: incremental compilation. That is, it should be possible,
in a legal program, to write a program such that, at run time, a
user can input code in the language, and have it compiled and execute,
and be able to do anything a programmer could do feeding the input
into a compiler. This need only be true "in principle", as obviously
for a large language writing a compiler is a large task. I 
am not aware of any (normally compiled as opposed to interpreted)
languages where this is true. Forth comes close, but C and Fortran
and Cobol and Pascal and friends all seem to make it impossible,
although it takes only a tiny little change to C (i.e. make it 
legal to cast a data pointer to a function pointer, and be able to
execute that function) to make it possible there. For many C
implementation it is de facto possible. 

What about Ada?

(I have not the foggiest idea about the answer.)

Doug McDonald