From a7bc3d426eec66623a66556cd849def2794bab73 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Mon, 14 May 2012 15:47:44 -0700
Subject: [PATCH] sets: adding ?adjoin.

---
 core/sets/sets-docs.factor | 5 +++++
 core/sets/sets.factor      | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/core/sets/sets-docs.factor b/core/sets/sets-docs.factor
index 4067948c0e..0a53ec9829 100644
--- a/core/sets/sets-docs.factor
+++ b/core/sets/sets-docs.factor
@@ -87,6 +87,11 @@ HELP: adjoin
 }
 { $side-effects "set" } ;
 
+HELP: ?adjoin
+{ $values { "elt" object } { "set" set } { "?" "a boolean" } }
+{ $description "A version of " { $link adjoin } " which returns whether the element was added to the set." }
+{ $notes "This is slightly less efficient than " { $link adjoin } " due to the initial membership test." } ;
+
 HELP: delete
 { $values { "elt" object } { "set" set } }
 { $description "Destructively removes " { $snippet "elt" } " from " { $snippet "set" } ". If the element is not present, this does nothing." $nl "Each mutable set type is expected to implement a method on this generic word." }
diff --git a/core/sets/sets.factor b/core/sets/sets.factor
index 0e08bb2bfc..6fdd4d3431 100644
--- a/core/sets/sets.factor
+++ b/core/sets/sets.factor
@@ -132,6 +132,9 @@ M: sequence cardinality
 : without ( seq set -- subseq )
     tester [ not ] compose filter ;
 
+: ?adjoin ( elt set -- ? )
+    2dup in? [ 2drop f ] [ adjoin t ] if ; inline
+
 ! Temporarily for compatibility
 
 : unique ( seq -- assoc )