[Haskell-cafe] What's the difference?

Dan Weston westondan at imageworks.com
Tue Apr 8 14:51:28 EDT 2008

Paul Johnson wrote:
> You can regard an "instance" declaration as an inference rule for the 
> type checker, with "=>" meaning "implies" (though I don't think its the 
> answer to your other question about names).

"implies" might be a bad word, because the direction is backwards:

Eq a => Ord a

is clearly false if read that "Eq a implies Ord a". It is Ord a that 
implies Eq a.

I just read it as "required for" myself.


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