Книги автора: Practical Common Lisp
Книга: Practical Common Lisp
Controlling Evaluation
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.[206] And PROGN
provides the ability to sequence a number of forms.
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