# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1480629986 -3600
# Node ID 79c82d827bbe2cefa22606bfb682810ee8802731
# Parent  77890dd7214eeda3868eeaab4f5cea4e830f4b90
Fixed the xrange implementation, removing incorrect NO_END interpretation,
adding start and end validation, adding string representations.
Moved range from the iterable module to the span module.
Added a test of ranges.

diff -r 77890dd7214e -r 79c82d827bbe lib/__builtins__/__init__.py
--- a/lib/__builtins__/__init__.py	Thu Dec 01 21:23:11 2016 +0100
+++ b/lib/__builtins__/__init__.py	Thu Dec 01 23:06:26 2016 +0100
@@ -75,7 +75,7 @@
 from __builtins__.file import file
 from __builtins__.float import float
 from __builtins__.int import int
-from __builtins__.span import xrange, slice
+from __builtins__.span import range, slice, xrange
 from __builtins__.iterator import itemiterator
 from __builtins__.list import list
 from __builtins__.long import long
@@ -92,7 +92,7 @@
 from __builtins__.comparable import cmp, hash
 from __builtins__.identity import callable, help, id, isinstance, issubclass, repr
 from __builtins__.io import open, raw_input, print_, sysfile
-from __builtins__.iterable import all, any, enumerate, filter, iter, len, map, max, min, range, reduce, reversed, sorted, sum, zip
+from __builtins__.iterable import all, any, enumerate, filter, iter, len, map, max, min, reduce, reversed, sorted, sum, zip
 from __builtins__.namespace import dir, globals, locals, vars
 from __builtins__.numeric import abs, divmod, pow, round
 
diff -r 77890dd7214e -r 79c82d827bbe lib/__builtins__/iterable.py
--- a/lib/__builtins__/iterable.py	Thu Dec 01 21:23:11 2016 +0100
+++ b/lib/__builtins__/iterable.py	Thu Dec 01 23:06:26 2016 +0100
@@ -3,7 +3,7 @@
 """
 Iteration-related functions.
 
-Copyright (C) 2015 Paul Boddie <paul@boddie.org.uk>
+Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -19,8 +19,6 @@
 this program.  If not, see <http://www.gnu.org/licenses/>.
 """
 
-from __builtins__.span import xrange
-
 def all(iterable): pass
 def any(iterable): pass
 def enumerate(iterable): pass
@@ -59,12 +57,6 @@
             lowest = arg
     return lowest
 
-def range(start_or_end, end=None, step=1):
-
-    "Implementation of range."
-
-    return list(xrange(start_or_end, end, step))
-
 def reduce(function, sequence, initial=None): pass
 def reversed(sequence): pass
 def sorted(iterable, cmp=None, key=None, reverse=False): pass
diff -r 77890dd7214e -r 79c82d827bbe lib/__builtins__/span.py
--- a/lib/__builtins__/span.py	Thu Dec 01 21:23:11 2016 +0100
+++ b/lib/__builtins__/span.py	Thu Dec 01 23:06:26 2016 +0100
@@ -3,7 +3,7 @@
 """
 Span-related objects.
 
-Copyright (C) 2015 Paul Boddie <paul@boddie.org.uk>
+Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -19,7 +19,9 @@
 this program.  If not, see <http://www.gnu.org/licenses/>.
 """
 
-class xrange(object):
+from __builtins__.sequence import _max, _min
+
+class xrange:
 
     "Implementation of xrange."
 
@@ -37,8 +39,32 @@
             self.end = end
 
         self.step = step
+
+        # Constrain the end according to the start and step.
+
+        if step > 0:
+            self.end = _max(self.start, self.end)
+        elif step < 0:
+            self.end = _min(self.start, self.end)
+        else:
+            raise ValueError(self.step)
+
         self.current = self.start
-        self.limited = self.end is not xrange.NO_END
+
+    def __str__(self):
+
+        "Return a string representation."
+
+        b = buffer([self.__name__, "(", self.start, ", ", self.end, ", ", self.step, ")"])
+        return str(b)
+
+    __repr__ = __str__
+
+    def __len__(self):
+
+        "Return the length of the range."
+
+        return (self.end - self.start) / self.step
 
     def __iter__(self):
 
@@ -50,9 +76,8 @@
 
         "Return the next item or raise a StopIteration exception."
 
-        if self.limited:
-            if self.step < 0 and self.current <= self.end or self.step > 0 and self.current >= self.end:
-                raise StopIteration()
+        if self.step < 0 and self.current <= self.end or self.step > 0 and self.current >= self.end:
+            raise StopIteration()
 
         current = self.current
         self.current += self.step
@@ -68,4 +93,10 @@
 
         get_using(xrange.__init__, self)(start_or_end, end, step)
 
+def range(start_or_end, end=None, step=1):
+
+    "Implementation of range."
+
+    return list(xrange(start_or_end, end, step))
+
 # vim: tabstop=4 expandtab shiftwidth=4
diff -r 77890dd7214e -r 79c82d827bbe tests/range.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/range.py	Thu Dec 01 23:06:26 2016 +0100
@@ -0,0 +1,18 @@
+l = range(0, 10)
+print l                     # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+print len(l)                # 10
+
+x = xrange(0, -10, -2)
+print x                     # __builtins__.span.xrange(0, -10, -2)
+print len(x)                # 5
+
+for i in x:
+    print i                 # 0
+                            # -2
+                            # -4
+                            # -6
+                            # -8
+
+x = xrange(0, -10, 2)
+print x                     # __builtins__.span.xrange(0, 0, 2)
+print len(x)                # 0