TIME Agreed. These are all correct ways of defining the same thing (the "power" of languages), and we need to pick whichever is useful depending on what we're

TIME Agreed. These are all correct ways of defining the same thing (the "power" of languages), and we need to pick whichever is useful depending on what we're trying to do. If we're trying to put a precise measure on the power of a language, PG's treelength seems to do the job perfectly. But how do we design a language which would create programs with the smallest tree length, or which would take the least time to write it? To answer this, it's best to consider how easily our basic mental structures can be expressed in the language. The concept of sets, lists, map, and reduce exist in our lives whether we know program or not. If a language contains or lets us easily express other embodied mental structures such as relations, tags, partitions, etc. easily, it will be more powerful than languages which don't.