[Haskell-cafe] haskell and reflection

Greg Meredith lgreg.meredith at biosimilarity.com
Tue Sep 11 12:43:39 EDT 2007


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

Best wishes,


On 9/11/07, Jules Bean <jules at jellybean.co.uk> wrote:
> 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

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