Question

I m reading the guide in learnyouahaskell.com . One sentence mentioned "where" can be shared globally, but no example was given, so where can I find some details, please?

"where bindings aren t shared across function bodies of different patterns. If you want several patterns of one function to access some shared name, you have to define it globally."

Answer 1

http://learnyouahaskell.com/syntax-in-Functions”rel=“nofollow” 第4章:职能中的协同效应:

where bindings aren t shared across function bodies of different patterns. If you want several patterns of one function to access some shared name, you have to define it globally.

Here is an illustration:

f (Left x) = double x
f (Right x) = double x
    where
    double x = 2 * x

The function f has a body for each of the patterns (Left x) and (Right x). The binding of double isn t shared across the function bodies, and therefore this code isn t valid Haskell.

If we want to access double from both of the function bodies, we have to move it out of the where clause:

double x = 2 * x

f (Left x) = double x
f (Right x) = double x

该款所引述的意思就是这样。

Answer 2

我认为,这意味着你必须界定一个新的<>功能。在全球范围,而不是在处。

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