为什么Elixir在UndefinedFunctionError
文件中使用Module.macroName
语法调用宏时报告.exs
?我似乎只能调用宏,如果我有另一个调用宏的函数,我调用函数而不是宏。
下面的代码演示了这一点:
defmodule Sample do
defmacro doIt(expression) do
quote do
IO.puts unquote(expression)
end
end
def doFunc(e), do: doIt(e)
end
Sample.doFunc "Hello World via Function" # Works fine
Sample.doIt "Hello World from Macro!" # Gives error
输出
Hello World via Function
** (UndefinedFunctionError) undefined function: Sample.doIt/1
Sample.doIt("Hello World from Macro!")
(elixir) lib/code.ex:307: Code.require_file/2
Elixir documentation示例使用iex
,而不是在.exs
文件中调用宏。即使是上面的代码,如果我们删除对Sample.doIt
的调用并将其加载到iex
中,然后调用Sample.doIt
也可以正常工作。
E:\elixir>iex hello.exs
Hello World via Function
Interactive Elixir (1.0.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> require Sample
nil
iex(2)> Sample.doIt "Hello"
Hello
:ok
iex(3)>
如果我在上面的文件中尝试require Sample
,如下所示
defmodule Sample
... rest of stuff as shown above ...
end
require Sample
Sample.doFunc "Hello World via Function"
Sample.doIt "Hello World from Macro!"
我收到错误
** (CompileError) hello.exs:11: module Sample is not loaded but was defined. This happens because you are trying to use a module in the same context it is defined. Try defining the module outside the context that requires it.
(stdlib) lists.erl:1352: :lists.mapfoldl/3
(stdlib) lists.erl:1353: :lists.mapfoldl/3
答案 0 :(得分:5)
像往常一样,在使用宏之前需要一个模块来向编译器表明编译模块的顺序:
defmodule Other do
def run do
require Sample
Sample.doFunc "Hello World via Function"
Sample.doIt "Hello World from Macro!"
end
end
Other.run # => Hello World via Function
# Hello World from Macro!