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(in-package :alexandria)
(defun featurep (feature-expression)
"Returns T if the argument matches the state of the *FEATURES*
list and NIL if it does not. FEATURE-EXPRESSION can be any atom
or list acceptable to the reader macros #+ and #-."
(etypecase feature-expression
(symbol (not (null (member feature-expression *features*))))
(cons (check-type (first feature-expression) symbol)
(eswitch ((first feature-expression) :test 'string=)
(:and (every #'featurep (rest feature-expression)))
(:or (some #'featurep (rest feature-expression)))
(:not (assert (= 2 (length feature-expression)))
(not (featurep (second feature-expression))))))))
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