Re: [Haskell-cafe] dependent types

11 Apr 2010


      On Sun, Apr 11, 2010 at 4:15 PM, Ozgur Akgun  wrote:
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On 11 April 2010 22:54, Jason Dagit  wrote:
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class Vehicle a where
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data Car
data Truck
instance Vehicle Car where
instance Vehicle Truck where
Now you can have things that take a Car or a Truck or they can take a
Vehicle instead.
moveVehicle :: Vehicle v => v -> Simulation ()
unfortunately, now you cannot use pattern matching while defining
moveVehicle.
That's true.  Although, if you're writing a simulation where Cars and Trucks
are objects in that simulation, they are likely to be defined as records as
they will probably have many fields.  If that's the case, it's unlikely
you'd be using pattern matching with them anyway.  It's just a small step
from there to using typeclass functions to access the parts you care about.

Jason