[Haskell-beginners] Type classes and synonyms

sterl s.clover at gmail.com
Sun Nov 22 13:08:24 EST 2009

Brent Yorgey wrote:
> "free theorem" will be of the form
>   "Any function f of type T, *no matter how f is implemented*, will
>   always satisfy the following property:
>     blah blah f blah = blah f blah
>   "
> This has nothing to do with whether or not there is only one possible
> implementation of f that does not involve undefined, which is a
> different phenomenon.
If it hasn't been mentioned, djinn turns type signatures into code, as 
has been discussed, although if f has multiple implementations, it will 
simply produce one of them.

The discussion on ltu helps flesh out the concept: 

This is, of course, as Brent pointed out, very different from free theorems.


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