为什么Haskell有非严格的函数（语义）？ [英] Why does Haskell have non-strict functions (semantics)?

问题描述

根据这篇关于 haskell中的指称语义的文章
所有类型都有底，如果一个函数f：A-> B是严格的，如果它将A类型的底部映射到B类型的底部，则称其为 non-strict 。

（这让人联想到态射保持基点的尖端类别）。

为什么Haskell没有 - 严格的函数，而标准的ML没有？

解决方案

每个带递归的至少一个非严格函数，通常以条件形式（ if-then-else ）。否则，所有的递归都会表示底部（非终止）。尽管非严格功能是必不可少的，但是，大多数这些语言不允许你自己定义！有些语言通过提供宏来弥补这一限制 - 这是一种类似于函数的机​​制，可以转换语法而不是值。

According to this article on denotational semantics in haskell All types have bottom, and a function f:A->B is strict if it maps the bottom of type A to the bottom of type B, it is called non-strict other-wise.

(This is reminiscent of a pointed category where morphisms preserve the basepoint).

Why does Haskell have non-strict functions, whereas Standard ML doesn't?

解决方案

Every programming language with recursion has at least one non-strict function, often in the form of a conditional (if-then-else). Otherwise all recursions would denote bottom (non-termination). Essential as non-strict functions are, however, most of these languages do not let you define your own! Some languages make up for this limitation by offering macros--a somewhat function-like mechanism that transforms syntax instead of values.

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