[Haskell-cafe] Re: Re: What *is* a DSL?

Ben Franksen ben.franksen at online.de
Mon Oct 12 17:05:17 EDT 2009

S. Doaitse Swierstra wrote:
> This problem of dynamically transforming grammars and bulding parsers
> out of it is addressed in:
> @inproceedings{1411296,
>   author = {Viera, Marcos and Swierstra, S. Doaitse and Lempsink,
> Eelco},
>   title = {Haskell, do you read me?: constructing and composing
> efficient top-down parsers at runtime},
> [...]
>   }

Indeed, it looks as if you solved exactly the problem that vexed me! I had
just found the presentation that corresponds to the paper you mention, and
I also found a preprint for "Typed transformations of Typed Abstract
Syntax" which I am studying at the moment. I must say your construction is,
well, involved...

Not that I want to belittle this really astounding and clever achievement...
but one disadvantage of your approach (which it shares with almost all
examples I have seen for dependently typed or heterogeneous collections) is
that (IIUC) the typed map from references to abstract syntactic terms is
operationally an association list, indexed by unary numbers. I would expect
this to scale poorly if the number of references (e.g. nonterminals) gets

I think it would make for quite an interesting research project to study
whether it is possible to achieve the same level of precise static typing
with more efficient data structures. I imagine that using some 'fake
dependent type' variant of [Bit] for the key and the equivalent of a
patricia tree for the map could perhaps be made to work???


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