Editing Lambda calculus (section)

=== Anonymous functions ===
{{Further|Anonymous function}}
For example, in [[Python (programming language)|Python]] the "square" function can be expressed as a lambda expression as follows:
<!-- Please do not add the same example in different languages to this article, see Anonymous function for that. Thank you! -->
<syntaxhighlight lang="Python">
(lambda x: x**2)
</syntaxhighlight>

The above example is an expression that evaluates to a first-class function. The symbol <code>lambda</code> creates an anonymous function, given a list of parameter names, <code>x</code> – just a single argument in this case, and an expression that is evaluated as the body of the function, <code>x**2</code>. Anonymous functions are sometimes called lambda expressions.

For example, [[Pascal (programming language)|Pascal]] and many other imperative languages have long supported passing [[Function (computer programming)|subprograms]] as [[Parameter (computer programming)|arguments]] to other subprograms through the mechanism of [[function pointer]]s. However, function pointers are an insufficient condition for functions to be [[First-class function|first class]] datatypes, because a function is a first class datatype if and only if new instances of the function can be created at [[Execution (computing)#runtime|runtime]]. Such runtime creation of functions is supported in [[Smalltalk]], [[JavaScript]], [[Wolfram Language]], and more recently in [[Scala (programming language)|Scala]], [[Eiffel (programming language)|Eiffel]] (as agents), [[C Sharp (programming language)|C#]] (as delegates) and [[C++11]], among others.