wren ng thornton | 21 Jul 04:43 2013

ANN: data-fin

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-- data-fin 0.1.0
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The data-fin package offers the family of totally ordered finite sets,
implemented as newtypes of Integer, etc. Thus, you get all the joys of:

    data Nat = Zero | Succ !Nat

    data Fin :: Nat -> * where
        FZero :: (n::Nat) -> Fin (Succ n)
        FSucc :: (n::Nat) -> Fin n -> Fun (Succ n)

But with the efficiency of native types instead of unary encodings.

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-- Notes
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I wrote this package for a linear algebra system I've been working on, but
it should also be useful for folks working on Agda, Idris, etc, who want
something more efficient to compile down to in Haskell. The package is
still highly experimental, and I welcome any and all feedback.

Note that we implement type-level numbers using [1] and [2], which works
fairly well, but not as nicely as true dependent types since we can't
express certain typeclass entailments. Once the constraint solver for
type-level natural numbers becomes available, we'll switch over to using
that.

(Continue reading)


Gmane