Re: The making of compilers

[dewar@gnat.com (Robert Dewar)]

"tony gair" <tonygair@nespamtome.btinternet.com> wrote in message news:<a5btuv$f62$1@knossos.btinternet.com>...
> After sticking my neck out and being shot out out of the sky by the big
> guns.....................................
> 
> I heard from a lecturer in 1990 that compilers were built 
> by writing a language subset compiler in assembler (or C 
> or C++ or.....) and then by using that subset to step by 
> step extend the language to its desired form.

Yes, that's indeed the most reasonable approach if there are no
existing compilers for the language. For example, Alsys Ada was
initially implemented using a subset compiler written in PL/1.

By the time GNAT was being created, the Alsys compiler
already existed, and we first wrote in Ada 83, and bootstrapped using
the Alsys compiler on a Sun, then once
we were bootstrapped, we step by step extended, so that
now we use quite a lot of Ada 95 features.

> And he was really clever he was , he had glasses and a 
> beard and everything.

I am not sure of the reason for this frivolous comment,
but he was giving a perfectly reasonable account of how
things are done. Your tone seems to indicate skepticism,
but in this case I am afraid the skepticism comes from
ignorance, and glasses-and-beard knew what he was talking
about :-)