Editing Pattern matching (section)

====Haskell====
In Haskell, the following line defines an algebraic data type <code>Color</code> that has a single data constructor <code>ColorConstructor</code> that wraps an integer and a string.

<syntaxhighlight lang="haskell">
data Color = ColorConstructor Integer String
</syntaxhighlight>

The constructor is a node in a tree and the integer and string are leaves in branches.

When we want to write [[function (programming)|functions]] to make <code>Color</code> an [[abstract data type]], we wish to write functions to [[Interface (computer science)|interface]] with the data type, and thus we want to extract some data from the data type, for example, just the string or just the integer part of <code>Color</code>.

If we pass a variable that is of type Color, how can we get the data out of this variable? For example, for a function to get the integer part of <code>Color</code>, we can use a simple tree pattern and write:

<syntaxhighlight lang="haskell">
integerPart (ColorConstructor theInteger _) = theInteger
</syntaxhighlight>

As well:
<syntaxhighlight lang="haskell">
stringPart (ColorConstructor _ theString) = theString
</syntaxhighlight>

The creations of these functions can be automated by Haskell's data [[Record (computer science)|record]] syntax.