Re: Formal semantics of language semantics

Nick Maclaren <nmm1@cus.cam.ac.uk> wrote:
>Ingo Dittmer <i.dittmer@fh-osnabrueck.de> wrote:
>>Many. All two-level-grammars (van-Wijngarden, [...]
>Hang on. The two-level grammars that I know of DON'T handle the
>semantics, but extend the syntax to things like the type rules. That
>was most definitely so for the van Wijngarden grammar used in Algol
>68, for example. [...]


It is true that the van Wijngaarden grammar used to define
Algol 68 in the RR did not attempt the semantics; but it is *also*
true that vW grammars *can* be used to define semantics%, and, as Ingo
said, this was being done from the '60s. I doubt whether it's
particularly useful to do so, but that's a different problem.


Cleaveland and Uzgalis showed in their book how to do this.
It could "easily" be extended to a purely grammatical way to "run" a
given piece of code on an abstract machine with a given input stream
so that the code parses to either a compilation error or else a
suitable output stream. Again, this is more of the nature of a proof
of concept rather than a practical way of writing a compiler and
running the resulting code ....


________
% At least, on the assumption that by "semantics" we mean something
    more than "what's left over after syntax". Otherwise, then of
    course shifting everything into the vWG doesn't do semantics, but
    rather shifts all the semantics into syntax.


--
Andy Walker, School of MathSci., Univ. of Nott'm, UK.
anw@maths.nott.ac.uk

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