Page:Scheme - An interpreter for extended lambda calculus.djvu/34



This is the central function of the SCHEME interpreter. This "instruction" expects  to contain an expression to evaluate, and   to contain the environment for the evaluation. The fact that we have arrived here indicates that  contains , and so we need not change   if the next instruction is also to be. Besides the obvious objects likes [sic] numbers, identifiers,  expressions, and   expressions (closures), there are also several other objects of interest. There are primitive operators (LISP functions); s (which are to SCHEME as  s like   are to LISP); and  s, which are used to implement ,  ,  ,  ,  , etc.