Let expression

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In computer science, a "let" expression associates a function definition with a restricted scope.

The "let" expression may also be defined in mathematics, where it associates a Boolean condition with a restricted scope.

The "let" expression may be considered as a lambda abstraction applied to a value. Within mathematics, a let expression may also be considered as a conjunction of expressions, within an existential quantifier which restricts the scope of the variable.

The let expression is present in many functional languages to allow the local definition of expression, for use in defining another expression. The let-expression is present in some functional languages in two forms; let or "let rec". Let rec is an extension of the simple let expression which uses the fixed-point combinator to implement recursion.