Haskell - 是什么让“主要"与众不同? [英] Haskell - What makes 'main' unique?

问题描述

使用此代码:

main :: FilePath -> FilePath -> IO ()
main wrPath rdPath = do x <- readFile rdPath
                        writeFile wrPath x

我收到以下错误:

Couldn't match expected type 'IO t0'
            with actual type 'FilePath -> FilePath -> IO()

但是当我将main"的名称更改为其他名称时，文件可以正确编译.

But the file compiles correctly when I change the name of 'main' to something else.

main 有什么独特之处，为什么它的类型必须是 IO t0?

What's so unique about main and why does its type have to be IO t0?

推荐答案

因为语言规范 这样说.

Haskell 程序是一组模块，按照惯例，其中一个模块必须称为 Main，并且必须导出值 main.程序的值是模块Main中标识符main的值，对于某种类型IO t，它必须是类型IO t的计算code>t(见第 7 章).程序执行时，执行计算main，其结果(t类型)被丢弃.

A Haskell program is a collection of modules, one of which, by convention, must be called Main and must export the value main. The value of the program is the value of the identifier main in module Main, which must be a computation of type IO t for some type t (see Chapter 7). When the program is executed, the computation main is performed, and its result (of type t) is discarded.

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