Controlling Evaluation
The first category of special operators contains the three operators that provide basic control over the evaluation of forms. They’re **QUOTE**
, **IF**
, and **PROGN**
, and I’ve discussed them all already. However, it’s worth noting how each of these special operators provides one fundamental kind of control over the evaluation of one or more forms. **QUOTE**
prevents evaluation altogether and allows you to get at s-expressions as data. **IF**
provides the fundamental boolean choice operation from which all other conditional execution constructs can be built.1 And **PROGN**
provides the ability to sequence a number of forms.
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