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600.429 FUNCTIONAL PROGRAMING AT WORK - HASKELL AND DOMAIN SPECIFIC LANGUAGES

600.429 FUNCTIONAL PROGRAMING AT WORK - HASKELL AND DOMAIN SPECIFIC LANGUAGES. Dr. John Peterson Western State Colorado University. Old Homework. http:// wiki.western.edu/mcis/index.php/429/Week_1 Questions?. Type Classes.

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600.429 FUNCTIONAL PROGRAMING AT WORK - HASKELL AND DOMAIN SPECIFIC LANGUAGES

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  1. 600.429FUNCTIONAL PROGRAMING AT WORK - HASKELL AND DOMAIN SPECIFIC LANGUAGES Dr. John Peterson Western State Colorado University

  2. Old Homework • http://wiki.western.edu/mcis/index.php/429/Week_1 • Questions?

  3. Type Classes • A type class specifies a set of abstract operations that can be associated with a particular type class Similar a where isSimilar:: a -> a -> Bool notSimilar :: a -> a -> BoolnotSimilar x y = not $ isSimilarx y

  4. Instances An instance associates a type with a class: instance Similar Int where isSimilarx y = abs (x-y) < 2 How is this similar to Java? Different?

  5. Qualifiers When you use a function in a class, this brings the class name into the type signature: find :: (Similar a) => a -> [a] -> Bool find v = not . null . filter (\x -> isSimilar v x)

  6. Constraints in instances instance (Similar a, Similar b) => Similar (a, b) where isSimilar (x1, y1) (x2, y2) = isSimilar x1 x2 || isSimilar y1 y2

  7. Superclasses class Similar a => SuperSim a where reallySimilar :: a -> a -> Bool instance SuperSimInt where reallySimilar x y = isSimilarx y && x < y

  8. Built-in Classes • Off to haskell.org

  9. Derived Instances • Automatic code generation! data Foo = Foo IntInt deriving Show

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