[Haskell-cafe] Slightly Offtopic in Part

[Stefan O'Rear]

On Fri, Feb 08, 2008 at 06:47:51PM -0800, Ryan Ingram wrote:
> I'm assuming you mean the rule described in
> http://en.wikibooks.org/wiki/Formal_Logic/Sentential_Logic/Inference_Rules
> 
> > type Disj a b = Either a b
> 
> > disj_elim :: Disj a b -> (a -> c) -> (b -> c) -> c
> > disj_elim (Left a) a2c b2c = a2c a
> > disj_elim (Right b) a2c b2c = b2c b
> 
> If you know "either a is true, or b is true"
> and you know "from a, I can prove c",
> and you know "from b, I can prove c",
> then you can prove c.

aka:

import Data.Either

type Disj = Either
disj_elim = either

Stefan
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