support -inf in /to/

Author: czheo

syntax_sugar/infix.py

@@ -21,14 +21,15 @@ def __rtruediv__(self, left):
 take = infix(compose(list, islice))
 
 INF = float('inf')
+NEGINF = float('-inf')
 
 class To:
     def __init__(self, start, end):
-        if start == INF: 
-            raise TypeError('Cannot start range from infinity')
+        if start in {INF, NEGINF}:
+            raise ValueError('Cannot start range from infinity')
 
         valid_char = lambda c: c /of/ str and len(c) == 1
-        valid_integer = lambda i: i /of/ int or i == INF
+        valid_integer = lambda i: i /of/ int or i == INF or i == NEGINF
 
         if valid_integer(start) and valid_integer(end):
             self.type = 'number'
@@ -127,6 +128,7 @@ def by(to_object, step):
     'to',
     'by',
     'INF',
+    'NEGINF',
     'hasattr',
     'fmap',
     'freduce',

tests/test_infix.py

@@ -69,6 +69,19 @@ def test_bad_step():
     with raises(ValueError):
         to_obj.step = 1
 
+def test_infinity():
+    with raises(ValueError):
+        INF /to/ 100
+
+    with raises(ValueError):
+        NEGINF /to/ 1
+
+    assert 1 /to/ INF /take/ 10 == list(range(1, 11))
+    assert 1 /to/ NEGINF /take/ 10 == list(range(1, -9, -1))
+
+    assert 1 /to/ INF /by/ 2 /take/ 10 == list(range(1, 100, 2))[:10]
+    assert 1 /to/ NEGINF /by/ 2 /take/ 10 == list(range(1, -100, -2))[:10]
+
 def test_take():
     assert 1 /to/ INF /take/ 5 == [1,2,3,4,5]