如何在 GHCi 中打印类型的构造函数？

Question

使用:t 我可以打印表达式的类型。但是我如何查看该类型的构造函数呢？在 emacs 的 Haskell 模式下也有快捷方式吗？

这似乎是一个基本的东西，但我找不到。也许我只是在搜索错误的术语...

一般来说，无需查看文档即可查看打印类型定义的最简单方法是什么。

Answer 1

:info，或者 :i，就是您想要的：

>>> :i Either
data Either a b = Left a | Right b  -- Defined in ‘Data.Either’
... plus all of Either's instances

来自GHCi documentation：

:info name ...

Displays information about the given name(s). For example, if name is a class, then the class methods and their types will be printed; if name is a type constructor, then its definition will be printed; if name is a function, then its type will be printed. If name has been loaded from a source file, then GHCi will also display the location of its definition in the source.

Haskell-Emacs 中的模式有 haskell-process-do-info（source), for which one Haskell on Emacs Tutorial 建议设置键绑定 C-c C-n C-i.

(defun haskell-process-do-info (&optional prompt-value) 
  "Print info on the identifier at point.
If PROMPT-VALUE is non-nil, request identifier via mini-buffer."
...
)

如何在 GHCi 中打印类型的构造函数？

How to print the constructors of a type in GHCi?

haskell

ghci

haskell-mode