Polymorphism: Difference between revisions
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[[Category:Glossary]] | [[Category:Glossary]] | ||
A value is | A value is polymorphic if, depending on the context where it's used, it can take on more than one type. | ||
There are different kinds of polymorphism. | |||
#[[Parametric polymorphism]]; mostly found in functional languages | #[[Parametric polymorphism]]; mostly found in functional languages | ||
#[[Ad-hoc polymorphism]] or overloading | |||
#[[Inclusion polymorphism]]; mostly found in object oriented languages | #[[Inclusion polymorphism]]; mostly found in object oriented languages | ||
== | == Examples == | ||
<haskell> | <haskell> | ||
foldr :: forall a b. (a -> b -> b) -> b -> [a] -> b | foldr :: forall a b. (a -> b -> b) -> b -> [a] -> b | ||
</haskell> | </haskell> | ||
<hask>foldr</hask> is a | <hask>foldr</hask> is a parametric polymorphic [[function]]. When actually used, it may take on any of a variety of types, for example: | ||
<haskell> | <haskell> | ||
::(Char ->Int->Int)->Int->String->Int | ::(Char ->Int->Int)->Int->String->Int | ||
::(String->String->String)->String->[String]->String | ::(String->String->String)->String->[String]->String | ||
</haskell> | </haskell> | ||
An "integer literal" is polymorphic: | An "integer literal" is a parametric polymorphic data type: | ||
<haskell> | <haskell> | ||
1 :: forall t. (Num t) => t | 1 :: forall t. (Num t) => t | ||
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== References == | == References == | ||
*[http://citeseer.nj.nec.com/cardelli85understanding.html On Understanding Types, Data Abstraction, and Polymorphism (1985)], by Luca Cardelli, Peter Wegner in ACM Computing Surveys. | *[http://citeseer.nj.nec.com/cardelli85understanding.html On Understanding Types, Data Abstraction, and Polymorphism (1985)], by Luca Cardelli, Peter Wegner in ACM Computing Surveys. | ||
*[http://en.wikipedia.org/wiki/Type_polymorphism Type polymorphism] at Wikipedia | |||
Revision as of 07:02, 6 October 2009
A value is polymorphic if, depending on the context where it's used, it can take on more than one type.
There are different kinds of polymorphism.
- Parametric polymorphism; mostly found in functional languages
- Ad-hoc polymorphism or overloading
- Inclusion polymorphism; mostly found in object oriented languages
Examples
foldr :: forall a b. (a -> b -> b) -> b -> [a] -> bfoldr is a parametric polymorphic function. When actually used, it may take on any of a variety of types, for example:
::(Char ->Int->Int)->Int->String->Int
::(String->String->String)->String->[String]->StringAn "integer literal" is a parametric polymorphic data type:
1 :: forall t. (Num t) => tReferences
- On Understanding Types, Data Abstraction, and Polymorphism (1985), by Luca Cardelli, Peter Wegner in ACM Computing Surveys.
- Type polymorphism at Wikipedia