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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. == History == Dana Scotts LCF language〔"PCF is a programming language for computable functions, based on LCF, Scott’s logic of computable functions" . ''Programming Computable Functions'' is used by . It is also referred to as ''Programming with Computable Functions'' or ''Programming language for Computable Functions''.〕 was a stage in the evolution of lambda calculus into modern functional languages. This language introduced the let expression, which has appeared in most functional languages since that time. The languages Scheme,〔 〕 ML, and more recently Haskell〔 〕 have inherited let expressions from LCF. State-full imperative languages such as ALGOL and Pascal essentially implement a let expression, to implement restricted scope of functions, in block structures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Let expression」の詳細全文を読む スポンサード リンク
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