From 782442afc8c5a3eeaccceadb35598b8a32666890 Mon Sep 17 00:00:00 2001
From: Kyle <kyle@tyrfingr.is>
Date: Tue, 1 Sep 2015 02:21:07 -0700
Subject: [PATCH] Add partition.

---
 docs/manual.scr |  5 +++++
 kutils.lisp     | 27 +++++++++++++++++++++++++++
 package.lisp    |  1 +
 3 files changed, 33 insertions(+)

diff --git a/docs/manual.scr b/docs/manual.scr
index 46cf899..0c255dc 100644
--- a/docs/manual.scr
+++ b/docs/manual.scr
@@ -133,6 +133,7 @@ some functions I found useful.)
 @cl:doc(function take)
 @cl:doc(function drop)
 @cl:doc(function partial)
+@cl:doc(function partition)
 )
 @end(def)
 
@@ -395,6 +396,9 @@ described in "Miscellaneous utilities" under "Vector-related".)
 @item(@c(partial) is a function defined in @c(kutils.lisp), described
 in "Miscellaneous utilities" under "Clojure-inspired functions".)
 
+@item(@c(partition) is a function defined in @c(kutils.lisp), described
+in "Miscellaneous utilities" under "Clojure-inspired functions".)
+
 @item(@c(read-file-as-string) is a macro defined in @c(macros.lisp),
 described in "Macros" under "File macros".)
 
@@ -475,6 +479,7 @@ Alphabetical documentation for all exported symbols.
 @cl:doc(function new-hash-table)
 @cl:doc(function new-vector)
 @cl:doc(function partial)
+@cl:doc(function partition)
 @cl:doc(macro sethash)
 @cl:doc(function symb)
 @cl:doc(function take)
diff --git a/kutils.lisp b/kutils.lisp
index 46a18de..a145eca 100644
--- a/kutils.lisp
+++ b/kutils.lisp
@@ -144,3 +144,30 @@ effectful code, such as logging."
       (apply fn args))))
 
 
+(defun partition-list (test lst)
+  (let (match no-match)
+    (dolist (x lst)
+      (if (funcall test x)
+	  (push x match)
+	  (push x no-match)))
+    (vector match no-match)))
+
+(defun partition-vector (test vec)
+  (let ((match (new-vector))
+	(no-match (new-vector)))
+    (dotimes (i (length vec))
+      (let ((x (aref vec i)))
+	(if (funcall test x)
+	    (vector-push-extend x match)
+	    (vector-push-extend x no-match))))
+    (list match no-match)))
+
+(defun partition (pred seq)
+  "Split @c(seq) into a pair of sequences with @c(pred) : the first of
+the pair are those elements satisfying @c(pred), and the second are
+those that do not satisfy @c(pred)."
+  (cond
+    ((listp seq)   (partition-list pred seq))
+    ((vectorp seq) (partition-vector pred seq))
+    (t (error "Values of type ~A cannot be partitioned."
+	      (type-of seq)))))
diff --git a/package.lisp b/package.lisp
index 0d2043b..2b754a8 100644
--- a/package.lisp
+++ b/package.lisp
@@ -30,6 +30,7 @@
 	   #:cartprod2
 	   #:empty-or-nil-p
 	   #:effector
+	   #:partition
 
 	   ;; kutils-hash-tables.lisp
            #:enable-hash-table-reader