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- variable which is the name of a primitive MacLISP function, or on a variable bound by LABELS. (ASET' is actually used very seldom in practice anyway, and all these restrictions are "good programming practice". RABBIT could be altered to lift these restrictions, at some expense and labor.)
- CATCH
- This provides an escape operator facility. [Landin] [Reynolds]
(CATCH var body)evaluates the body, which may refer to the variable var, which will denote an "escape function" of one argument which, when called, will return from the CATCH-form with the given argument as the value of the CATCH-form. Note that it is entirely possible to return from the CATCH-form several times. This raises a difficulty with optimization which will be discussed later. - Macros
- Any atomic symbol which has been defined in one of various ways to be a macro distinguishes a special construct whose meaning is determined by a macro function. This function has the responsibility of rewriting the form and returning a new form to be evaluated in place of the old one. In this way complex syntactic constructs can be expressed in terms of simpler ones.
