# HG changeset patch
# User Steve Losh <steve@stevelosh.com>
# Date 1470937459 0
# Node ID e14d7729f02a38e07bb624f8a4b39828504d7d70
# Parent  2991413e9fa6131f2e390d84e11cd52b2d55222d
Add `nullary`

diff -r 2991413e9fa6 -r e14d7729f02a losh.lisp
--- a/losh.lisp	Thu Aug 11 00:08:21 2016 +0000
+++ b/losh.lisp	Thu Aug 11 17:44:19 2016 +0000
@@ -192,6 +192,30 @@
   (lambda (&rest args)
     (mapcar (rcurry #'apply args) fns)))
 
+(defun nullary (function &optional result)
+  "Return a new function that acts as a nullary-patched version of `function`.
+
+  The new function will return `result` when called with zero arguments, and
+  delegate to `function` otherwise.
+
+  Examples:
+
+    (max 1 10 2)                     => 10
+    (max)                            => invalid number of arguments
+
+    (funcall (nullary #'max))        => nil
+    (funcall (nullary #'max 0))      => 0
+    (funcall (nullary #'max) 1 10 2) => 10
+
+    (reduce #'max nil)                  => invalid number of arguments
+    (reduce (nullary #'max) nil)        => nil
+    (reduce (nullary #'max :empty) nil) => :empty
+    (reduce (nullary #'max) '(1 10 2))  => 10
+
+  "
+  (lambda (&rest args)
+    (if (null args) result (apply function args))))
+
 
 ;;;; Control Flow
 (defmacro recursively (bindings &body body)