Hello, I understand using _ as a Wildcard pattern is considered "out of question" and now work is made to make the __ available for that purpose.

My question is, why is _ out of question?

I understand _ might be in use already, but is this really a problem?

The way I see it, there 2 cases _ might be in use:

As an identifier
As a macro

In the first case _ might be interpreted as "something else" - an existing variable, a typename or function name. However in the context of Pattern Matching this will not be a problem as _ can only be used in places where a variable identifier is expected AND by default all variable identifiers are NOT referencing existing ones - they are introducing new ones. In other words, per current PM rules _ can never ever be interpreted as anything different then a Wildcard.

The second case, having some _ macro. These cases will clash as the macro will expand before PM is evaluated. This means one can't use Wildcard AND have some _ macro visible. Is this a show-stopping problem though? It is not that we are breaking user code. Or making _ a global keyword. It is just that you can't have both that macro, that you can rename, and PM with a Wildcard.

Am I missing something? What is the official reason _ can't be used in PM?

Thank You