I'm a heavy user of ghc-typelits-natnormalise.

I can feel your pain that it sometimes isn't able to solve seemingly "simple" constraints. But not all is lost in those cases. The `constraints` package allows one to solve `Nat` constraints out of thin air, provided you go through a function to do it.

nLEZeroIsZeroRule :: (n <= 0) :- (n ~ 0)
nLEZeroIsZeroRule = Sub (unsafeCoerce (Dict :: Dict (a ~ a)))

Good to know that there are ways to add missing transformations.

Ideally there would be a way without unsafeCoerce, i.e. that I could prove a property manually using some proof steps expressed in functions.

I also developed [type-natural] package, which comes with the showcase of arithmetic lemma.
This builds on [equational-reasoning] package to make proof-writing easier.

[type-natural]: https://hackage.haskell.org/package/type-natural
[equational-reasoning]: https://hackage.haskell.org/package/equational-reasoning

-- Hiromi ISHII
konn.jinro@gmail.com



2023/01/13 19:02、Henning Thielemann <lemming@henning-thielemann.de>のメール:


On Fri, 13 Jan 2023, rowan goemans wrote:

I'm a heavy user of ghc-typelits-natnormalise.

I can feel your pain that it sometimes isn't able to solve seemingly "simple" constraints. But not all is lost in those cases. The `constraints` package allows one to solve `Nat` constraints out of thin air, provided you go through a function to do it.

nLEZeroIsZeroRule :: (n <= 0) :- (n ~ 0)
nLEZeroIsZeroRule = Sub (unsafeCoerce (Dict :: Dict (a ~ a)))

Good to know that there are ways to add missing transformations.

Ideally there would be a way without unsafeCoerce, i.e. that I could prove a property manually using some proof steps expressed in functions.


Alternatively, maybe I can write missing steps in a custom type checker plugin.


Has someone already tried to connect SBV to a type checker plugin?
_______________________________________________
Haskell-Cafe mailing list
To (un)subscribe, modify options or view archives go to:
http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
Only members subscribed via the mailman list are allowed to post.