Jules,
Thanks for these comments. i wouldn't judge Haskell solely on the basis of
whether it embraced reflection as an organizing computational principle or
as a toolbox for programmers. Clearly, you can get very far without it. And,
it may be that higher-order functional gives you enough of the 'programs
that build programs' capability that 80% of the practical benefits of
reflection are covered -- without having to take on the extra level of
complexity that reflection adds to typing. i was really just seeking
information.
Best wishes,
--greg
On 9/11/07, Jules Bean
Greg Meredith wrote:
Haskellians,
Am i wrong in my assessment that the vast majority of reflective machinery is missing from Haskell? Specifically,
* there is no runtime representation of type available for programmatic representation * there is no runtime representation of the type-inferencing or checking machinery * there is no runtime representation of the evaluation machinery * there is no runtime representation of the lexical or parsing machinery
As far as they go, those are true.
Haskell compiler are permitted to erase types and GHC does so. There is no need to check types at runtime; that's the point of the system! There is no evaluator, or parser, built in to the standard libraries. (The lexer, or a version of it, is embedded in actual fact but that's not very exciting).
However, one should not draw too strong negative conclusions from this. It is possible to get suprisingly far with more powerful, more typesafe techniques without surrendering the the pure dynamism of languages that lack compile-time guarantees. Deriving Typeable and Data is one tool which is useful.
It is quite possible to embed a haskell compiler, see hs-plugins.
Jules
-- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com