Implement parameterised rules

[david-pfx]

The basic idea is to use the existing label syntax, but allow labels to be passed as parameters into a rule, where it can be used as a rule, or to replace a literal, or to pass into another rule.

IronMeta has this feature.

[otac0n]

This is a duplicate of #32.

[david-pfx]

If you say so, but it was intended to be something much simpler.

Rule1 = "foo" / Error("foo expected");
Rule2 = "bar" / Error("bar expected");
Error(m) = #STATE{ Error(m); } Skip;

Basically just a way to avoid some repetition.

[otac0n]

It can't quite be that simple:

Error ("foo expected")

This is ambiguous between a parameterized rule and a sequence.

[david-pfx]

So it would appear. The usual way of resolving this ambiguity is by significant whitespace.

Error ("foo expected") // sequence
Error("foo expected") // rule with parameter

The compiler will pick up any errors, assuming the rule either does or does not have a parameter.