understanding syb boilerplate elimination

Posted by Pradeep on Stack Overflow See other posts from Stack Overflow or by Pradeep
Published on 2010-04-07T16:00:45Z Indexed on 2010/04/07 16:03 UTC
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haskell

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boilerplate

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generics

In the example given in http://web.archive.org/web/20080622204226/http://www.cs.vu.nl/boilerplate/

-- Increase salary by percentage
increase :: Float -> Company -> Company
increase k = everywhere (mkT (incS k))

-- "interesting" code for increase
incS :: Float -> Salary -> Salary
incS k (S s) = S (s * (1+k))

how come increase function compiles without binding anything for the first Company mentioned in its type signature.

Is it something like assigning to a partial function? Why is it done like that?

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