Erlang“未绑定变量”当调用函数时 [英] Erlang "unbound variable" when calling a function

问题描述

我试图将一个整数参数N传递给 cake ，并返回一个大小为N的平方的列表（为了示例的目的）。例如面包店：蛋糕（3）=> [4,4,4]

I am trying to pass an integer parameter N to cake and return a list of size N of the square of 2 (for the sake of example). e.g. bakery:cake(3) => [4,4,4]

这是我迄今为止所尝试的：

Here is what I have attempted so far:

-module(bakery).
-export([cake/1]).

Foo = fun(X) -> X * X end.

cake(0) -> [];
cake(N) when N > 0 -> [ Foo(2) | cake(N-1) ].

当我编译代码 c（bakery）。在erl中，我得到以下错误跟踪：

When I compile the code c(bakery). in erl however, I get the following error trace:

bakery.erl:4:  syntax error before: Foo
bakery.erl:7:  variable 'Foo' is unbound
error

我是仍然习惯于匿名功能和erlang一般来说面向对象的世界。任何帮助将不胜感激。

I am still getting used to anonymous functions and erlang in general coming an object-oriented world. Any help would be appreciated.

推荐答案

每个Erlang模块，如这里应该包含一系列属性和函数声明，每个都由句号（。）终止。

Each Erlang module, as described here, should consist of a sequence of attributes and function declarations, each terminated by period (.)

但这行：

Foo = fun(X) -> X * X end.

...既不是，也应该写成如下：

... is neither and should be written as follows instead:

foo(X) -> X * X.

foo 是小写在这里因为此行是函数声明，其中函数名应为原子码。

foo is lowercase here, because this line is a function declaration, where function name should be an atom.

所以最后你的模块看起来像这样：

So in the end your module will look like this:

-module(bakery).
-export([cake/1]).

foo(X) -> X * X.

cake(0) -> [];
cake(N) when N > 0 -> [ foo(2) | cake(N-1) ].

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