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| ANSI Common Lisp 24 System Construction 24.1 System Construction Concepts 24.1.2 Features ### 24.1.2.1 Feature Expressions Boolean combinations of features, called feature expressions, are used by the `#+` and `#-` reader macros in order to direct conditional reading of expressions by the Lisp reader. The rules for interpreting a feature expression are as follows: feature If a symbol naming a feature is used as a feature expression, the feature expression succeeds if that feature is present; otherwise it fails. `(not feature-conditional)` A not feature expression succeeds if its argument feature-conditional fails; otherwise, it succeeds. `(and {feature-conditional}*)` An and feature expression succeeds if all of its argument feature-conditionals succeed; otherwise, it fails. `(or {feature-conditional}*)` An or feature expression succeeds if any of its argument feature-conditionals succeed; otherwise, it fails. 24.1.2.1.1 Examples of Feature Expressions

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