however, one could still deal with functions (i.e. closures) as such, for that ability is part of the fundamental environment and control facilities. Conversely, in a SCHEME which does have CONS, CAR, and CDR, there is no defined way to use CONS by itself to construct a function (although a primitive ENCLOSE is now provided which converts an S-expression representation of a function into a function), and the CAR or CDR of a function is in general undefined. The only defined operation on a function is invocation. {Note Operations on Functions}
We draw this sharp distinction between environment and control constructs on the one hand and data manipulation primitives on the other because only the former are treated in any depth by RABBIT, whereas much of the knowledge of a "real" compiler deals with the latter. A PL/I compiler must have much specific knowledge about numbers, arrays, strings, and so on. We have no new ideas to present here on such issues, and so have avoided this entire area. RABBIT itself knows almost nothing about data manipulation primitives beyond being able to recognize them and pass them along to the output code, which is a small subset of MacLISP. In this way RABBIT can concentrate on the interesting issues of environment and control, and exploit the expert knowledge of data manipulation primitives already built into the MacLISP compiler.
