# Lambda abstraction

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A *lambda abstraction* is another name for an anonymous function. It gets its name from the usual notation for writing it - for example, . (Note: some sources write it as .)

\

->

\ x -> x * x

There is actually a whole mathematical theory devoted to expressing computation entirely using lambda abstractions - the lambda calculus. Most functional programming languages (including Haskell) are based upon some extension of this idea.

When a lambda abstraction is applied to a value - for instance, - the result of the expression is determined by replacing every occurrence of the parameter variable (in this case *x*) with the parameter value (in this case 7). This is an eta reduction.