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.