Is the pattern matching broken?

[seb321]

Hi,

I am looking for c++ preprocessor / macro system. I have found this project, but it seems that it is either broken or has an odd semantics. For example, I would expect this macro not to match.

macro foo {
	case {
		match {
			( $(a) )
		}
		template {
			$(a)
		}
	}
}

foo()

However, it matches, yet $(a) has undefined value, so we get an error Unknown variable: 'a'.

It is possible to prevent this situation by matching against a pair of empty parentheses prior to the original pattern.

macro foo {
	case {
		match { () }
		template { /**/ }
	}
	case {
		match { ( $(a) ) }
		template { $(a) }
	}
}

foo ()

This time macro succeeds and it results in /**/. Unfortunately, it seems not to work with @splice.

macro bar {
	case {
		match { ( $(block list) ) }
		template { foo ( $(@splice block) ) }
	}
}

bar (())

Once again we get Unknown variable: 'a' error. When we change foo for some placeholder then the macro succeeds and expands into placeholder (), so in case of foo it should expand into foo (), which expands into /**/, but it does not happen.

Is this a bug or intentional behaviour?

[caffe3]

Sorry, I've been looking at this project today and fixing some of the outstanding issues. The way it behaves here is a little strange but ($(a)) should be equivalent to writing $(a) without the brackets - i.e cmacro is treating these are expressions.

From what I've understood from your question, it looks like you are hoping that it is matching on the () itself... I don't think this is the intended to work in cmacro. However, the error Unknown variable: 'a' is still a bug in itself.