[antlr-interest] NQOT: Grammar meta-programming

[Gavin Lambert]

At 05:02 8/12/2007, Andy Tripp wrote:
>On the other hand...one approach I've thought about would be to 
>use programming-by-example.
>You feed your magic tool sets of examples: "Here is a program, 
>and here is the AST that
>it should produce". If you can make your set of examples 
>exhaustive (i.e. cover all language constructs), that seems like 
>it might work.
>
>So the tool could store its grammar in whatever format it wants 
>(ANTLR or something completely different), but you'd essentially 
>define your parser not as a traditional BNF-style grammar, but 
>rather as a set of example (input, AST) pairs.

That'd be pretty cool.  Although I suspect in practice you'd 
probably need to have an (input, token stream, AST) triplet (or 
sets of input=>tokens and sets of tokens=>ASTs).  Going straight 
from input to AST is probably a bit too hard :)

Actually even the first half of that (input => token stream) would 
be a big help in many cases.  Since ANTLR doesn't have much 
debugging support for lexers, it's easy to accidentally break 
something in weird ways (especially if you don't have unit tests).
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