A macro can't modify an argument, it always receives immutable objects or copies of Expr trees. This is not at all similar to how a function accepts a reference to an object. If you are using `eval` in your macro to mutate a variable, stop right now. Replace all your macros with functions. Then go read the chapter on macros.
On Saturday, May 14, 2016 at 2:52:08 AM UTC-4, Ford Ox wrote: > > Shouldn't macro use the same principle as functions? That is: > > If your macro changes the value of variable you passed as argument (say > @increment x), thus it works similar to a function accepting pointer, it > should be marked with "!" at the end? (@increment! x) > > If your macro changes variables that you even didn't pass in as an > argument (say @increment() always increments x from outer scope), then the > macro should be marked with "!!" at the end? (@increment!!) OR it could be > marked with "![variable name]![variable name].... (@increment!x(), > @increment!x!y!z() ...) > > I am not sure whether somebody wants to ever use the second type the > macro, but if yes, people should definitely know about that without the > need to read inner body of that macro. > > What do you think? Should we make it a rule similar to functions that > change their arguments? > > (I hope its not already in docs and I just skipped that chapter :D) >
