[Haskell-cafe] [ANN]: fin & vec
Oleg Grenrus
oleg.grenrus at iki.fi
Tue Nov 21 14:14:16 UTC 2017
Thanks for more references! I was quite sure I didn't found all packages
around fin/nat/vec (and I feel a little bad for making "standards"
problem worse :)
- https://hackage.haskell.org/package/finite-typelits uses
GHC.TypeLits.Nat (fair thing to do).
- https://hackage.haskell.org/package/vector-sized builds on top of that
and looks like a nice package too!
I dislike GHC.TypeLits.Nat for doing induction over, yet for many things
they (+ [1,2] or [3]) are great. I have to write that down in the
description of the package(s). Hopefully the approaches: compiler
built-in magic and DataKinds definition would be unified in the future.
Cheers, Oleg.
- [1] https://hackage.haskell.org/package/ghc-typelits-natnormalise
- [2] https://hackage.haskell.org/package/ghc-typelits-extra
- [3]
http://hackage.haskell.org/package/constraints-0.9.1/docs/Data-Constraint-Nat.html
On 21.11.2017 15:20, Alexey Vagarenko wrote:
> I wrote a package not long ago which also uses static inlining for
> similar things: https://hackage.haskell.org/package/static-tensor
>
> There is also https://hackage.haskell.org/package/vector-sized which
> is a wrapper around 'vector' library.
>
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>
> 2017-11-21 17:27 GMT+05:00 Oleg Grenrus <oleg.grenrus at iki.fi
> <mailto:oleg.grenrus at iki.fi>>:
>
> I'm happy to announce two packages:
>
> - http://hackage.haskell.org/package/fin
> <http://hackage.haskell.org/package/fin>
> - http://hackage.haskell.org/package/vec
> <http://hackage.haskell.org/package/vec>
>
> In short they provide following types:
>
> data Nat where Z | S Nat
>
> data Fin (n :: Nat) where
> Z :: Fin ('S n)
> S :: Fin n -> Fin ('S n)
>
> data Vec (n :: Nat) a where
> VNil :: Vec 'Z a
> (:::) :: a -> Vec n a -> Vec ('S n) a
>
> Main motivation for creating these packages is that I didn't found
> anything
> similar on Hackage. Before comparison with the alternatives, let me
> mention few
> highlights:
>
> - `fin` and `vec` support GHC-7.8.4 .. GHC-8.2.1; and I plan to
> keep support
> window as wide as possible.
>
> - `fin` package provides `Data.Fin.Enum` module to work
> generically with
> enumerations. It's (subjectively) more ergonomic than working with
> `All ((:~:) a) xs => NS I xs` from `generics-sop` [1]
>
> - `fin` package defines `InlineInduction` class,
> letting us trick GHC to unfold recursion. One general example is
>
> unfoldedFix :: forall n a proxy. InlineInduction n
> => proxy n -> (a -> a) -> a
> unfoldedFix _ = getFix (inlineInduction1 start step :: Fix
> n a)
> where
> start :: Fix 'Z a
> start = Fix fix
>
> step :: Fix m a -> Fix ('S m) a
> step (Fix go) = Fix $ \f -> f (go f)
>
> newtype Fix (n :: Nat) a = Fix { getFix :: (a -> a) -> a }
>
> So, for statically known @n@, GHC's inliner will "simplify":
>
> unfoldedFix (Proxy :: Proxy Nat3) f = f (f (f (fix f)))
>
> - `fin` has very light dependency footprint:
> `base`, `deepseq`, `hashable` (and transitively `text`) on GHC>=8.0
>
> - `vec` has a little more dependencies, essentially `lens`. See
> dependency
> diagram in the readme. [2]
>
> - `vec` comes in three flavours:
>
> * __naive__: with explicit recursion. It's simple,
> constraint-less,
> yet slow.
>
> * __pull__: using `Fin n -> a` representation, which fuses well,
> but makes some programs hard to write. And
>
> * __inline__: which uses `InlineInduction`, unrolling
> recursion if the size of 'Vec' is known statically.
>
> Differences with other packages
> -------------------------------
>
> ### fin
>
> - [type-natural](http://hackage.haskell.org/package/type-natural
> <http://hackage.haskell.org/package/type-natural>) depends
> on @singletons@ package. `fin` will try to stay light on the
> dependencies,
> and support as many GHC versions as practical.
>
> - [peano](http://hackage.haskell.org/package/peano
> <http://hackage.haskell.org/package/peano>) is very incomplete
>
> - [nat](http://hackage.haskell.org/package/nat
> <http://hackage.haskell.org/package/nat>) as well.
>
> -
> [PeanoWitnesses](https://hackage.haskell.org/package/PeanoWitnesses
> <https://hackage.haskell.org/package/PeanoWitnesses>)
> doesn't use @DataKinds at .
>
> -
> [type-combinators](http://hackage.haskell.org/package/type-combinators
> <http://hackage.haskell.org/package/type-combinators>)
> is a big package.
>
> ### vec
>
> - [linear](http://hackage.haskell.org/package/linear
> <http://hackage.haskell.org/package/linear>) has 'V' type,
> which uses 'Vector' from @vector@ package as backing store.
> `Vec` is a real GADT, but tries to provide as many useful
> instances (upto
> @lens@).
>
> - [sized-vector](http://hackage.haskell.org/package/sized-vector
> <http://hackage.haskell.org/package/sized-vector>) depends
> on 'singletons' package. `vec` isn't light on dependencies either,
> but try to provide wide GHC support.
>
> - [sized](https://hackage.haskell.org/package/sized
> <https://hackage.haskell.org/package/sized>) also depends
> on a 'singletons' package. The 'Sized f n a' type is
> generalisation of
> linears 'V' for any 'ListLike'.
>
> -
> [clash-prelude](https://hackage.haskell.org/package/clash-prelude
> <https://hackage.haskell.org/package/clash-prelude>)
> is a kitchen sink package, which has 'CLaSH.Sized.Vector' module.
> Also depends on 'singletons'.
>
> Disclaimer
> ----------
>
> These are the "first released versions", i.e. `fin-0` and `vec-0`.
> Don't be fooled by 0, we use them in production.
>
> We don't have (yet?) a use-case where proper full inlining would
> matter, it
> seems to work with simple examples. The `vec` package includes
> simple dot
> product benchmark, it gives sensible results:
>
> - *list* version sets the baseline, built-in fusion seems to kick in.
> - using `vector` is 3x slower (?)
> - naive `Vec` is even slower, not surprisingly
> - `Data.Vec.Pull` approach is slower, *except*
> - that without conversions it's up to speed with `vector`
> - `InlineInduction` is *fastest*.
>
> Acknowledgements
> ----------------
>
> - *APLicative Programming with Naperian Functors* [3] has the very
> similar
> `Nat`, `Fin` and `Vec` (sections 2--4). I spotted few missing
> functions in
> `vec` by re-reading the paper (`vgroup` is `chunks` and `viota` is
> `universe`).
> I don't claim that my library is novel in any kind :)
> - I learned *Pull array* idea from Josef Svenningsson talk at SmallFP
> 2017 [4].
> See the video [5] if interested.
> - Herbert Valerio Riedel for the idea to split `fin` out of `vec`.
> It turned
> out to be very light package.
> - Andres Löh for discussions about `generics-sop` [1], and about
> the static
> inlining idea.
> - Joachim Breitner for creating `inspection-testing` [6], which
> really helps
> validating optimisations working.
>
> Cheers,
> Oleg
>
>
> - [1] http://hackage.haskell.org/package/generics-sop
> <http://hackage.haskell.org/package/generics-sop>
> - [2] https://github.com/phadej/vec#dependencies
> <https://github.com/phadej/vec#dependencies>
> - [3]
> https://www.cs.ox.ac.uk/people/jeremy.gibbons/publications/aplicative.pdf
> <https://www.cs.ox.ac.uk/people/jeremy.gibbons/publications/aplicative.pdf>
> - [4] http://clojutre.org/2017/
> - [5]
> https://www.youtube.com/watch?v=5PZh0BcjIbY&list=PLetHPRQvX4a9uUK2JUZrgjtC_x4CeNLtN&index=5
> <https://www.youtube.com/watch?v=5PZh0BcjIbY&list=PLetHPRQvX4a9uUK2JUZrgjtC_x4CeNLtN&index=5>
> - [6] http://hackage.haskell.org/package/inspection-testing
> <http://hackage.haskell.org/package/inspection-testing>
>
>
>
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