Haskell - 是什么让 'main' 独一无二？

Question

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。

main 有什么独特之处？为什么它的类型必须是 IO t0？

Answer 1

因为语言规范says so .

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.