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| Parametric polymorphism is when a function's type signature allows various arguments to take on arbitrary types, but the types must be ''related'' to each other in some way. | | #REDIRECT [[Polymorphism#Parametric polymorphism]] |
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| For example, in Java one can write a function that accepts two arguments of any possible type. However, Haskell goes further by allowing a function to accept two arguments of any type so long as they are both ''the same'' type. For example
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| As a specific (and slightly more complicated) example, the well-known <hask>map</hask> function has a parametrically polymorphic type
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| <haskell>
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| map :: (a -> b) -> [a] -> [b]
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| </haskell>
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| which means that the function well accept ''any'' type of list and ''any'' type of function, '''provided''' the types match up. This makes <hask>map</hask> highly polymorphic, yet there is still no risk of a runtime type mismatch.
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