haskell - 从模块中导出类型运算符

Question

你如何导出类型运算符？考虑到它们可能与普通运算符发生冲突，如果可能的话，必须有一个特殊的语法。

Answer 1

我在 7.4.4 of the GHC User's Guide 部分找到了答案，其中指出:

There is now some potential ambiguity in import and export lists; for example if you write import M( (+) ) do you mean the function (+) or the type constructor (+)? The default is the former, but with -XExplicitNamespaces (which is implied by -XExplicitTypeOperators) GHC allows you to specify the latter by preceding it with the keyword type, thus:

import M( type (+) )

虽然看起来您实际上不需要指定 -XExplicitNamespaces ，也许 -XExplicitTypeOperators是一个错字，意思是 -XTypeOperators .一些更多的经验证据:

★ → :set -XExplicitTypeOperators
Some flags have not been recognized: -XExplicitTypeOperators