[marcofiset]

> Also you can't pattern match on a function return value IIRC.

You definitely can. A function return value is just any other value and you can pattern match on it directly, or with the `case` or `with` constructs.

[throwawaymaths]

I think the poster means "you can't pattern match with a function value

[marcofiset]

I don't see how this would be useful.

[conradfr]

What would be the correct way to pattern match here?

  def foo(<I want to pattern match the value returned by GreatModule.constant_substitute()>), do: "bar"
 
  def foo(value), do: value

[marcofiset]

Use a `case` in the body of the function. Why do you absolutely need to pattern match in the function header?