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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Weak Head Normal Form ： FOLDOC Weak Head Normal Form (WHNF) A lambda expression is in weak head normal form (WHNF) if it is a head normal form (HNF) or any lambda abstraction. I.e. the top level is not a redex. The term was coined by {Simon Peyton Jones} to make explicit the difference between head normal form (HNF) and what graph reduction systems produce in practice. A lambda abstraction with a reducible body, e.g. x . (( y . y+x) 2) is in WHNF but not HNF. To reduce this expression to HNF would require reduction of the lambda body: ( y . y+x) 2 --> 2+x Reduction to WHNF avoids the name capture problem with its need for alpha conversion of an inner lambda abstraction and so is preferred in practical graph reduction systems. The same principle is often used in strict languages such as Scheme to provide call-by-name evaluation by wrapping an expression in a lambda abstraction with no arguments: D = call-by-name evaluation by wrapping an expression in a lambda abstraction with no arguments: D = スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.