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author | Vincent Ambo <tazjin@google.com> | 2020-01-17T18·04+0000 |
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committer | Vincent Ambo <tazjin@google.com> | 2020-01-17T18·04+0000 |
commit | 95aeb2ebae32a01ff79644daa523bda5d8552863 (patch) | |
tree | 551a1efe85e43fe6fd963a35b9b787a04a12dce3 /control-flow.lisp |
Squashed 'third_party/lisp/alexandria/' content from commit fc2a2f5c
git-subtree-dir: third_party/lisp/alexandria git-subtree-split: fc2a2f5c34147bb4e3e4a350b04220de0263710f
Diffstat (limited to 'control-flow.lisp')
-rw-r--r-- | control-flow.lisp | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/control-flow.lisp b/control-flow.lisp new file mode 100644 index 000000000000..dd00df3e1620 --- /dev/null +++ b/control-flow.lisp @@ -0,0 +1,106 @@ +(in-package :alexandria) + +(defun extract-function-name (spec) + "Useful for macros that want to mimic the functional interface for functions +like #'eq and 'eq." + (if (and (consp spec) + (member (first spec) '(quote function))) + (second spec) + spec)) + +(defun generate-switch-body (whole object clauses test key &optional default) + (with-gensyms (value) + (setf test (extract-function-name test)) + (setf key (extract-function-name key)) + (when (and (consp default) + (member (first default) '(error cerror))) + (setf default `(,@default "No keys match in SWITCH. Testing against ~S with ~S." + ,value ',test))) + `(let ((,value (,key ,object))) + (cond ,@(mapcar (lambda (clause) + (if (member (first clause) '(t otherwise)) + (progn + (when default + (error "Multiple default clauses or illegal use of a default clause in ~S." + whole)) + (setf default `(progn ,@(rest clause))) + '(())) + (destructuring-bind (key-form &body forms) clause + `((,test ,value ,key-form) + ,@forms)))) + clauses) + (t ,default))))) + +(defmacro switch (&whole whole (object &key (test 'eql) (key 'identity)) + &body clauses) + "Evaluates first matching clause, returning its values, or evaluates and +returns the values of T or OTHERWISE if no keys match." + (generate-switch-body whole object clauses test key)) + +(defmacro eswitch (&whole whole (object &key (test 'eql) (key 'identity)) + &body clauses) + "Like SWITCH, but signals an error if no key matches." + (generate-switch-body whole object clauses test key '(error))) + +(defmacro cswitch (&whole whole (object &key (test 'eql) (key 'identity)) + &body clauses) + "Like SWITCH, but signals a continuable error if no key matches." + (generate-switch-body whole object clauses test key '(cerror "Return NIL from CSWITCH."))) + +(defmacro whichever (&rest possibilities &environment env) + "Evaluates exactly one of POSSIBILITIES, chosen at random." + (setf possibilities (mapcar (lambda (p) (macroexpand p env)) possibilities)) + (if (every (lambda (p) (constantp p)) possibilities) + `(svref (load-time-value (vector ,@possibilities)) (random ,(length possibilities))) + (labels ((expand (possibilities position random-number) + (if (null (cdr possibilities)) + (car possibilities) + (let* ((length (length possibilities)) + (half (truncate length 2)) + (second-half (nthcdr half possibilities)) + (first-half (butlast possibilities (- length half)))) + `(if (< ,random-number ,(+ position half)) + ,(expand first-half position random-number) + ,(expand second-half (+ position half) random-number)))))) + (with-gensyms (random-number) + (let ((length (length possibilities))) + `(let ((,random-number (random ,length))) + ,(expand possibilities 0 random-number))))))) + +(defmacro xor (&rest datums) + "Evaluates its arguments one at a time, from left to right. If more than one +argument evaluates to a true value no further DATUMS are evaluated, and NIL is +returned as both primary and secondary value. If exactly one argument +evaluates to true, its value is returned as the primary value after all the +arguments have been evaluated, and T is returned as the secondary value. If no +arguments evaluate to true NIL is retuned as primary, and T as secondary +value." + (with-gensyms (xor tmp true) + `(let (,tmp ,true) + (block ,xor + ,@(mapcar (lambda (datum) + `(if (setf ,tmp ,datum) + (if ,true + (return-from ,xor (values nil nil)) + (setf ,true ,tmp)))) + datums) + (return-from ,xor (values ,true t)))))) + +(defmacro nth-value-or (nth-value &body forms) + "Evaluates FORM arguments one at a time, until the NTH-VALUE returned by one +of the forms is true. It then returns all the values returned by evaluating +that form. If none of the forms return a true nth value, this form returns +NIL." + (once-only (nth-value) + (with-gensyms (values) + `(let ((,values (multiple-value-list ,(first forms)))) + (if (nth ,nth-value ,values) + (values-list ,values) + ,(if (rest forms) + `(nth-value-or ,nth-value ,@(rest forms)) + nil)))))) + +(defmacro multiple-value-prog2 (first-form second-form &body forms) + "Evaluates FIRST-FORM, then SECOND-FORM, and then FORMS. Yields as its value +all the value returned by SECOND-FORM." + `(progn ,first-form (multiple-value-prog1 ,second-form ,@forms))) |