optimize [+]

There is now also a sum function which calls into a sum method.
Any.sum is 10-20% faster than the generic reduce routine, while
Range.sum is O(N) faster. :)

src/core/Any.pm

@@ -11,6 +11,9 @@ my class X::Subscript::Negative { ... }
 
 my role  Numeric { ... }
 
+# We use a sentinel value to mark the end of an iteration.
+my constant IterationEnd = Mu.CREATE;
+
 my class Any { # declared in BOOTSTRAP
     # my class Any is Mu {
 
@@ -407,6 +410,15 @@ my class Any { # declared in BOOTSTRAP
     method print-nl() { self.print(self.nl-out) }
 
     method lazy-if($flag) { self }  # no-op on non-Iterables
+
+    method sum() {
+        my \iter = self.iterator;
+        my $sum = 0;
+        until (my \value = iter.pull-one) =:= IterationEnd {
+            $sum := $sum + value;
+        }
+        $sum;
+    }
 }
 Metamodel::ClassHOW.exclude_parent(Any);
 
@@ -463,6 +475,8 @@ multi sub elems($a) { $a.elems }
 proto sub end(|) { * }
 multi sub end($a) { $a.end }
 
+sub sum(Any \SELF) { SELF.sum }
+
 sub classify( $test, +items, *%named ) {
     if %named.EXISTS-KEY("into") {
         my $into := %named.DELETE-KEY("into");

src/core/Iterator.pm

@@ -1,6 +1,3 @@
-# We use a sentinel value to mark the end of an iteration.
-my constant IterationEnd = Mu.CREATE;
-
 # The Iterator role defines the API for an iterator and provides simple
 # fallback implementations for most of it, so any given iterator can pick
 # and choose what bits it can implement better for performance and/or

src/core/Range.pm

@@ -478,6 +478,12 @@ my class Range is Cool does Iterable does Positional {
     method pop(|) is nodal {
         X::Immutable.new(:typename<Range>, :method<pop>).throw
     }   
+
+    method sum() {
+        my ($start,$stop) = self.int-bounds;
+        my $elems = $stop - $start + 1;
+        ($start + $stop) * $elems / 2;
+    }
 }
 
 sub infix:<..>($min, $max) is pure {

src/core/metaops.pm

@@ -171,7 +171,10 @@ multi sub METAOP_REDUCE_LEFT(\op) {
 #?if jvm
         my $ :=
 #?endif
-        sub (+values) {
+
+        op =:= &infix:<+>
+        ?? &sum
+        !! sub (+values) {
             my \iter = values.iterator;
             my \first = iter.pull-one;
             return op.() if first =:= IterationEnd;