From 5bfea58ffb9fd731131bbbd3f3d077cb69c5f419 Mon Sep 17 00:00:00 2001
From: def <dennis@felsin9.de>
Date: Mon, 14 Jul 2014 15:03:09 +0200
Subject: [PATCH 1/3] Add missing difference and  to sets module

---
 lib/pure/collections/sets.nim | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/pure/collections/sets.nim b/lib/pure/collections/sets.nim
index 4ba67cb2e4..2f0c4d3d2d 100644
--- a/lib/pure/collections/sets.nim
+++ b/lib/pure/collections/sets.nim
@@ -167,6 +167,12 @@ proc intersection*[A](s1, s2: TSet[A]): TSet[A] =
   for item in s1:
     if item in s2: incl(result, item)
 
+proc difference*[A](s1, s2: TSet[A]): TSet[A] =
+  ## returns a new set of all items that are contained in `s1`, but not in `s2`
+  result = s1
+  for item in s2:
+    if contains(result, item): excl(result, item)
+
 proc symmetricDifference*[A](s1, s2: TSet[A]): TSet[A] =
   ## returns a new set of all items that are contained in either
   ## `s1` or `s2`, but not both
@@ -182,6 +188,10 @@ proc `*`*[A](s1, s2: TSet[A]): TSet[A] {.inline.} =
   ## alias for `intersection`
   result = intersection(s1, s2)
 
+proc `-`*[A](s1, s2: TSet[A]): TSet[A] {.inline.} =
+  ## alias for `difference`
+  result = difference(s1, s2)
+
 proc `-+-`*[A](s1, s2: TSet[A]): TSet[A] {.inline.} =
   ## alias for `symmetricDifference`
   result = symmetricDifference(s1, s2)

From 68c3c8ebfafbcd169bceaf2bebed8f7af8dbf124 Mon Sep 17 00:00:00 2001
From: def <dennis@felsin9.de>
Date: Mon, 14 Jul 2014 17:56:19 +0200
Subject: [PATCH 2/3] More effificent TSet difference

---
 lib/pure/collections/sets.nim | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/pure/collections/sets.nim b/lib/pure/collections/sets.nim
index 2f0c4d3d2d..f1eed00042 100644
--- a/lib/pure/collections/sets.nim
+++ b/lib/pure/collections/sets.nim
@@ -169,9 +169,10 @@ proc intersection*[A](s1, s2: TSet[A]): TSet[A] =
 
 proc difference*[A](s1, s2: TSet[A]): TSet[A] =
   ## returns a new set of all items that are contained in `s1`, but not in `s2`
-  result = s1
-  for item in s2:
-    if contains(result, item): excl(result, item)
+  result = initSet[A]()
+  for item in s1:
+    if not contains(s2, item):
+      incl(result, item)
 
 proc symmetricDifference*[A](s1, s2: TSet[A]): TSet[A] =
   ## returns a new set of all items that are contained in either

From 54d61d2f665d47e361cad6c6c1075a9aca2de4d3 Mon Sep 17 00:00:00 2001
From: def <dennis@felsin9.de>
Date: Tue, 15 Jul 2014 02:16:12 +0200
Subject: [PATCH 3/3] Add TSet difference tests

---
 tests/sets/tsets3.nim | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/tests/sets/tsets3.nim b/tests/sets/tsets3.nim
index d2b15d72d1..f599f8e7d6 100644
--- a/tests/sets/tsets3.nim
+++ b/tests/sets/tsets3.nim
@@ -74,8 +74,27 @@ block symmetricDifference:
   assert((s3 -+- s3) == initSet[int]())
   assert((s3 -+- s1) == s1_s3)
 
+block difference:
+  let
+    s1_s2 = difference(s1, s2)
+    s1_s3 = difference(s1, s3)
+    s2_s3 = s2 - s3
+
+  assert s1_s2.len == 2
+  assert s1_s3.len == 5
+  assert s2_s3.len == 3
+
+  for i in s1:
+    assert i in s1_s2 xor i in s2
+    assert i in s1_s3 xor i in s3
+  for i in s2:
+    assert i in s2_s3 xor i in s3
+
+  assert((s2 - s2) == initSet[int]())
+  assert((s1 - s3 - s1) == s1 -+- s3)
+
 block disjoint:
   assert(not disjoint(s1, s2))
   assert disjoint(s1, s3)
   assert(not disjoint(s2, s3))
-  assert(not disjoint(s2, s2))
\ No newline at end of file
+  assert(not disjoint(s2, s2))