It's nice to have the data/declarative notion of an instruction. It's even nicer to have this notion be exactly the same notion by which you cause effects via y

It's nice to have the data/declarative notion of an instruction. It's even nicer to have this notion be exactly the same notion by which you cause effects via your language. This means that all effectual code you encounter can, at least in principle, be analyzed as a declarative data structure.