Replacing name of a functor turns it into a symbol

[rexim]

noq> shape f(a, b, c)
shaping f(a, b, c)
> apply rule f = g
 => g
> done
noq>

[rexim]

Oh, it's actually by design. f is recognized as a variable that matches the whole expression. This is confusing nonetheless.

[rexim]

We can resolve the confusion by introducing a special kind of expressions "variable" and use it for binding the sub-expressions instead of symbols. And match the symbols literally.

The variables can be denoted by capitalizing first character of the name. Similar to how Prolog does it.