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authorVincent Ambo <tazjin@google.com>2020-01-17T18·04+0000
committerVincent Ambo <tazjin@google.com>2020-01-17T18·04+0000
commit95aeb2ebae32a01ff79644daa523bda5d8552863 (patch)
tree551a1efe85e43fe6fd963a35b9b787a04a12dce3 /features.lisp
Squashed 'third_party/lisp/alexandria/' content from commit fc2a2f5c
git-subtree-dir: third_party/lisp/alexandria
git-subtree-split: fc2a2f5c34147bb4e3e4a350b04220de0263710f
Diffstat (limited to 'features.lisp')
-rw-r--r--features.lisp14
1 files changed, 14 insertions, 0 deletions
diff --git a/features.lisp b/features.lisp
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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))))))))