Overloading

• Type classes are something like object classes in Java

• Several different types might be instances of the same class

• This means they must support some basic set of operations

• For example, any type t might be an instance of the Show class

• If so, there must be a function show of type t -> String

• The Haskell standard library makes all the standard types instances of Show

• So for example:

         show 137               yields    "137"
         show True              yields    "True"
         show "Foo"             yields    "\"Foo\""

• If you define your own type, you can define a show method

• And you can declare your type to be an instance of Show

• Notation:

        Show Integer            ("Integer is an instance of Show")
        Show Bool               ("Bool is an instance of Show")
        Show [Char]             ("[Char] is an instance of Show")

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Copyright © 1999,2008 Mark Dominus