True, 'if 3' will stay there if there is no rewrite for it. You can also use treat a lack of possible rewrite as an error, this is what the Tao 3D document desc

True, 'if 3' will stay there if there is no rewrite for it. You can also use treat a lack of possible rewrite as an error, this is what the Tao 3D document description language does. You'd get an error like "No form matches 'if 3'". Underneath, there is a rewrite operator, ->, that means to transform the shape on the left into the shape on the right. The precise semantics are a tiny bit more complicated than that, but it iterates until there is no more transformation that applies. Some specific rewrites will be transformed into "opcodes" of the underlying machine model. So A+B with integers on each side will execute an addition (the inner representation of the transform is something like A+B -> opcode Add). For more details, you can read http://xlr.sourceforge.net/sites/default/files/XLRef.pdf http://xlr.sourceforge.net/sites/default/files/XLRef.pdf. I badly need to update it, it's out of date, I have a more recent version, but I need to learn the new way to connect to SourceForge.