1 files changed, 89 insertions, 0 deletions
diff --git a/lib/system/setops.nim b/lib/system/setops.nim
new file mode 100644
index 000000000..67aa3097a
--- /dev/null
+++ b/lib/system/setops.nim
@@ -0,0 +1,89 @@
+func incl*[T](x: var set[T], y: T) {.magic: "Incl".} =
+  ## Includes element `y` in the set `x`.
+  ##
+  ## This is the same as `x = x + {y}`, but it might be more efficient.
+  runnableExamples:
+    var a = {1, 3, 5}
+    a.incl(2)
+    assert a == {1, 2, 3, 5}
+    a.incl(4)
+    assert a == {1, 2, 3, 4, 5}
+
+when not defined(nimHasCallsitePragma):
+  {.pragma: callsite.}
+
+template incl*[T](x: var set[T], y: set[T]) {.callsite.} =
+  ## Includes the set `y` in the set `x`.
+  runnableExamples:
+    var a = {1, 3, 5, 7}
+    var b = {4, 5, 6}
+    a.incl(b)
+    assert a == {1, 3, 4, 5, 6, 7}
+  x = x + y
+
+func excl*[T](x: var set[T], y: T) {.magic: "Excl".} =
+  ## Excludes element `y` from the set `x`.
+  ##
+  ## This is the same as `x = x - {y}`, but it might be more efficient.
+  runnableExamples:
+    var b = {2, 3, 5, 6, 12, 54}
+    b.excl(5)
+    assert b == {2, 3, 6, 12, 54}
+
+template excl*[T](x: var set[T], y: set[T]) {.callsite.} =
+  ## Excludes the set `y` from the set `x`.
+  runnableExamples:
+    var a = {1, 3, 5, 7}
+    var b = {3, 4, 5}
+    a.excl(b) 
+    assert a == {1, 7}
+  x = x - y
+
+func card*[T](x: set[T]): int {.magic: "Card".} =
+  ## Returns the cardinality of the set `x`, i.e. the number of elements
+  ## in the set.
+  runnableExamples:
+    var a = {1, 3, 5, 7}
+    assert card(a) == 4
+    var b = {1, 3, 5, 7, 5}
+    assert card(b) == 4 # repeated 5 doesn't count
+
+func len*[T](x: set[T]): int {.magic: "Card".}
+  ## An alias for `card(x)`.
+
+
+func `*`*[T](x, y: set[T]): set[T] {.magic: "MulSet".} =
+  ## This operator computes the intersection of two sets.
+  runnableExamples:
+    assert {1, 2, 3} * {2, 3, 4} == {2, 3}
+
+func `+`*[T](x, y: set[T]): set[T] {.magic: "PlusSet".} =
+  ## This operator computes the union of two sets.
+  runnableExamples:
+    assert {1, 2, 3} + {2, 3, 4} == {1, 2, 3, 4}
+
+func `-`*[T](x, y: set[T]): set[T] {.magic: "MinusSet".} =
+  ## This operator computes the difference of two sets.
+  runnableExamples:
+    assert {1, 2, 3} - {2, 3, 4} == {1}
+
+func contains*[T](x: set[T], y: T): bool {.magic: "InSet".} =
+  ## One should overload this proc if one wants to overload the `in` operator.
+  ##
+  ## The parameters are in reverse order! `a in b` is a template for
+  ## `contains(b, a)`.
+  ## This is because the unification algorithm that Nim uses for overload
+  ## resolution works from left to right.
+  ## But for the `in` operator that would be the wrong direction for this
+  ## piece of code:
+  runnableExamples:
+    var s: set[range['a'..'z']] = {'a'..'c'}
+    assert s.contains('c')
+    assert 'b' in s
+    assert 'd' notin s
+    assert set['a'..'z'] is set[range['a'..'z']]
+  ## If `in` had been declared as `[T](elem: T, s: set[T])` then `T` would
+  ## have been bound to `char`. But `s` is not compatible to type
+  ## `set[char]`! The solution is to bind `T` to `range['a'..'z']`. This
+  ## is achieved by reversing the parameters for `contains`; `in` then
+  ## passes its arguments in reverse order.