common: member and delete-dups convenience.

* common.el (durand-delete-dups): This uses a custom hash-table to
test for the equality.  Hence it can support custom equality-tests.
This function grew out of a function I wrote for eshell.

(durand-member): This is a convenient function to test for membership
in a list.  The implementationi is nothing new.  But it is
convenient.

1 files changed, 62 insertions, 0 deletions

diff --git a/common.el b/common.el
index b17787b..0417da5 100644
--- a/common.el
+++ b/common.el
@@ -331,6 +331,68 @@ completely hiding it."
                    (list (or ,light ""))))))
    (`(setcdr (assq ',minor minor-mode-alist) (list (or ,light ""))))))
 
+;;;###autoload
+(defun durand-delete-dups (sequence &rest args)
+  "Delete duplicate elements in SEQUENCE.
+If the keyword argument TEST is non-nil, it should be a function
+with two arguments which tests for equality of elements in the
+sequence. The default is the function `equal'.
+
+If the keyword argument KEY is non-nil, it should be a function
+with one argument which returns the key of the element in the
+sequence to be compared by the test function. The default is the
+function `identity'.
+
+Note that this function is not supposed to change global state,
+including match data, so the functions in TEST and KEY are
+supposed to leave the global state alone as well.
+
+\(fn SEQUENCE &key TEST KEY)"
+  (declare (pure t) (side-effect-free t))
+  (let* ((len (length sequence))
+         (temp-obarray (obarray-make len))
+         (valid-key-num (+ (cond ((plist-member args :key) 1) (0))
+                           (cond ((plist-member args :test) 1) (0))))
+         (key (cond ((cadr (plist-member args :key)))
+                    (#'identity)))
+         (test-fn (cond ((cadr (plist-member args :test)))
+                        (#'equal)))
+         found-table result)
+    (cond ((or (= (mod (length args) 2) 1)
+               (> (length args) (* 2 valid-key-num)))
+           (user-error "Invalid keyword arguments. Only :key and :test are allowed, but got %S"
+                       args)))
+    ;; Note: This just puts a property to the symbol.
+    (define-hash-table-test 'durand-delete-dups-test
+      test-fn (function (lambda (obj) (intern (format "%S" obj) temp-obarray))))
+    (setq found-table (make-hash-table :test 'durand-delete-dups-test :size len))
+    (mapc
+     (function
+      (lambda (element)
+        (cond ((gethash (funcall key element) found-table))
+              ;; Abuse the fact that `puthash' always returns VALUE.
+              ((puthash (funcall key element) t found-table)
+               (setq result (cons element result))))))
+     sequence)
+    (nreverse result)))
+
+;;;###autoload
+(defun durand-member (element ls &optional test)
+  "Return the tail of LS whose car is ELT.
+Comparison is done by TEST if that is non-nil, else by `equal'."
+  (let ((temp (copy-tree ls))
+        (not-found t))
+    (while (and not-found (consp temp))
+      (cond
+       ((and test
+             (funcall test element (car temp)))
+        (setq not-found nil))
+       (test (setq temp (cdr temp)))
+       ((equal element (car temp))
+        (setq not-found nil))
+       ((setq temp (cdr temp)))))
+    temp))
+
 (provide 'common)
 ;;; common.el ends here.