[antlr-interest] Re: how useful would a generic grammar "action" language be?
lgcraymer
lgc at mail1.jpl.nasa.gov
Tue Oct 28 09:54:28 PST 2003
--- In antlr-interest at yahoogroups.com, "Arnar Birgisson" <arnarb at o...>
wrote:
> How would the user clarify to ANTLR whether he/she is writing their
> actions in the target language, or the abstract action language?
Since Ter is just starting to investigate, this is clearly TBD. I
would personally favor only having actions in the "action language"; I
believe that this can be done for type declarations with a
configuration file which includes type definitions so that types can
be referred to by name in the ANTLR grammar and you can hide the
qualifiers and language specificity in the config file. Almost
anything can be encapsulated with a function call, so it should not be
too difficult to define a small action language. Most of the
complexity is likely to be in dealing with expressions.
> Having grammars with actions and all (even just the simple ones)
would
> be very cool, and it would help out alot when people distribute
grammars
> and/or use grammars from others. But if the implementation of this
would
> mean alot of work, is it worth it?
There is already an action filter for each target language, and I
suspect that a port of the action language would only be slightly more
work than writing a filter. One of my minor complaints has been that
AST class code should be generated from specifications and there
should be an ANTLR way of referencing instance variables (attributes)
in a non-language-specific way. Having an action language would be a
good way to address that.
There are some big wins possible here. Consider the fairly common
problem of retargeting a language grammar--to go from a java
environment to C# or C++ or OCaml, for example.
--Loring
> Arnar
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