未定义函数生成函数

Question

I am trying to generate 100 functions using metaprogramming in Elixir

I want the function to return a value that is computed during compile time

def func(0) do
  "you have 0 chances"
end

def func(1) do
  "you have 1 chances"
end

...

def func(100) do
  "you have 100 chances"
end

My first attempt was

0..100 |> Enum.each fn val ->
    def func(unquote(val)) do
        val_string = to_string(unquote(val))
        "you have " <> val_string <> " chances"
    end
end

But I have reason to believe that this just returns 100 functions that aren't evaluated during compile time.

Finally I tried this

0..100 |> Enum.each fn vol ->
  defmacro func(unquote(vol) = vol) do
    quote do
      "you have " <>  unquote(vol) <> " chances" |> unquote
    end
  end
end

but when I require the file and I call func(1) in iex I get

** (CompileError) iex:2: undefined function func/1

Is my defmacro logic correct in the first place? Any idea what I could be doing wrong.

Answer 1

First, just in case, you can acheive the same thing with a regular function, without metaprogramming:

def func(num) when is_integer(num) and 0 <= num and num <= 100 do
  "you have #{num} chances"
end

But if you are practising metaprogramming, remember that you need to unquote any of the compile-time variables:

for i <- 0..100 do
  def func(unquote(i)) do
    "You have #{unquote(i)} chances"
  end
end