Ruby builder needs to be able to build literals from Ruby constants

[louismrose]

Suppose we have the following program:

net * VAT

We cannot currently construct Metamorpher terms to match this program using the Ruby builder:

require "metamorpher"
built = Metamorpher.builder.build("net * VAT")  # => send(send(, net), *, VAT) 
built.children.last # => VAT
built.children.last.class #= > Metamorpher::Terms::Variable

This is because all uppercase constants are treated as variables, but in this case we wish to treat VAT as a literal.

[louismrose]

One solution might be to add a way of "whitelisting" constants to the builder:

require "metamorpher"
Metamorpher.builder.with_constants("VAT").build("net * VAT")

or

require "metamorpher"
Metamorpher.builder.build("net * VAT").ignoring("VAT")

The latter is perhaps a bit less intuitive (and would require the builder to undo the rewriting of terms that it has already rewritten from constants to variables!)