为什么odd.fst不能与过滤器功能一起使用? [英] Why does odd.fst not work with the filter function?

问题描述

为什么filter odd.fst [(1,2), (2,3)]给我一个编译错误? odd.fst应该接受一个整数元组并输出一个布尔值，所以我对为什么编译器告诉我它不能匹配类型感到困惑.

Why does filter odd.fst [(1,2), (2,3)] give me a compile error? odd.fst should take in a tuple of ints and output a boolean, so I am confused as to why the compiler is telling me it can't match types.

推荐答案

出于相同的原因，2 * 3+4是10，而不是14.运算符优先级不关心空格:2 * 3+4解析为(2 * 3) + 4.

For the same reason that 2 * 3+4 is 10, not 14. Operator precedence does not care about spacing: 2 * 3+4 parses as (2 * 3) + 4.

类似地，

filter odd.fst [(1,2), (2,3)]

解析为

(filter odd) . (fst [(1,2), (2,3)])

无论您如何排列它.这是因为函数应用程序的优先级高于任何中缀运算符.

no matter how you space it. This is because function application has higher precedence than any infix operator.

你想要

filter (odd . fst) [(1,2), (2,3)]

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