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From: mfeldman@seas.gwu.edu (Michael Feldman)
Newsgroups: comp.lang.ada
Subject: Re: Ada Interpreter question
Message-ID: <3418@sparko.gwu.edu>
Date: 29 Jun 91 16:54:55 GMT
References: <9106281209.AA08681@ajpo.sei.cmu.edu>
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Reply-To: mfeldman@seas.gwu.edu (Michael Feldman)
Organization: The George Washington University, Washington, D.C.
List-Id: <comp.lang.ada>

In article <9106281209.AA08681@ajpo.sei.cmu.edu> SAHARBAUGH@ROO.FIT.EDU writes:
>Is NYU Ada/ED defined to be an "Ada Interpreter".  The version
>I I used from 1983 to 1987 required a complete processing of the
>source code before it would then begin to interpret the
>intermediate code it had produced.
>In about 1984 Robert Dewar said to me "You really don't expect
>to ever be able to interpret Ada code?"
Ada/Ed is loosely called an interpreter. Actually, it's known officially as 
"executable semantic model." The Ada source is translated into an
intermediate form, then the intermediate form is interpreted. Whether
you call the first pass (source->IF) a "compiler" is splitting hairs.
It is certainly a translator. In a sense, Ada/Ed is a front end without
the back end, since most compilers produce some sort of IF (attributed
trees or suchlike). Ada/Ed just stops there.

>Then a few years later the people at Westinghouse said they
>would soon have the ability to interpret the complete Ada
>language.  Is their effort the ACE mentioned in the posting?
>Is ACE an interpreter by my definition?  ( For a demonstration
>of my definition of an interpreter go to your PC and type BASIC).

The version of ACE that I copied from STARS and built on our Sun indeed
seems to be an interpreter. But at least this version supports a sort
of "Pascal subset" of Ada. It seems to be designed less as a full 
interpreter for Ada than the sort of portable shell interpreter we were
all going to have as a part of the magical APSE.

Are my observations correct here? I haven't tested ACE extensively yet,
and maybe I'm underestimating its capability. If it's really intended as
an Ada interpreter for a really signficant part of the language (meaning
full data structures, generics, packages, maybe even tasking), is there
any schedule for its completion, or is it in the "real soon now"
category?

My bottom line: nice as far as it goes, lets you write "shell scripts"
using Ada procedure syntax, etc. But doesn't go nearly far enough. Or
have I missed a key bit of the documentation?

Mike