Thanks, this explanation is what I was looking for. Wikipeidia has an explanation on it also:
http://en.wikipedia.org/wiki/System_F#System daryoush On Wed, Feb 18, 2009 at 2:08 AM, Stephan Friedrichs < deduktionstheo...@web.de> wrote: > Daryoush Mehrtash wrote: > > Is there a way to define a type with qualification on top of existing > > type (e.g. prime numbers)? Say for example I want to define a > > computation that takes a prime number and generates a string. Is there > > any way I can do that in Haskell? > > Haskell's type system is decidable, so you can't let the type system > check arbitrary properties. It probably is possible in C++ by some > template hack (C++ templates are Turing complete), but not in Haskell. > But, as mentioned in the other responses, you can > > - use a representation that makes it impossible to use wrong values > (-> Ketil's n-th prime representation) > > - check values at runtime (-> Luke's repsonse) > > //Stephan > > -- > > Früher hieß es ja: Ich denke, also bin ich. > Heute weiß man: Es geht auch so. > > - Dieter Nuhr > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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