Builtin collection types should always evaluate as True (#566)

* Builtin collection types should always evaluate as True

* Fix next definition

* Change the log

Author: chrisrink10

CHANGELOG.md

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Fixed a bug where `deftype` forms could not be created interfaces declared not at the top-level of a code block in a namespace (#376)
  * Fixed multiple bugs relating to symbol resolution of `import`ed symbols in various contexts (#544)
  * Fixed a bug where the `=` function did not respect the equality partition for various builtin collection types (#556)
+ * Fixed a bug where collection types could evaluate as boolean `false` (#566)
 
 ## [v0.1.dev13] - 2020-03-16
 ### Added

src/basilisp/lang/list.py

@@ -22,6 +22,9 @@ def __init__(self, wrapped: "PList[T]", meta=None) -> None:
         self._inner = wrapped
         self._meta = meta
 
+    def __bool__(self):
+        return True
+
     def __getitem__(self, item):
         if isinstance(item, slice):
             return List(self._inner[item])

src/basilisp/lang/map.py

@@ -39,6 +39,9 @@ def __init__(
         self._inner = _Map(members)
         self._meta = meta
 
+    def __bool__(self):
+        return True
+
     def __call__(self, key, default=None):
         return self._inner.get(key, default)
 

src/basilisp/lang/runtime.py

@@ -900,10 +900,7 @@ def nthrest(coll, i: int):
 def next_(o) -> Optional[ISeq]:
     """Calls rest on o. If o returns an empty sequence or None, returns None.
     Otherwise, returns the elements after the first in o."""
-    s = rest(o)
-    if not s:
-        return None
-    return s
+    return to_seq(rest(o))
 
 
 def nthnext(coll, i: int) -> Optional[ISeq]:

src/basilisp/lang/seq.py

@@ -11,7 +11,7 @@ def __repr__(self):
         return "()"
 
     def __bool__(self):
-        return False
+        return True
 
     @property
     def meta(self) -> Optional[IPersistentMap]:

src/basilisp/lang/set.py

@@ -28,6 +28,9 @@ def __init__(self, members: Optional[Iterable[T]], meta=None) -> None:
         self._inner = _Map((m, m) for m in (members or ()))
         self._meta = meta
 
+    def __bool__(self):
+        return True
+
     def __call__(self, key, default=None):
         if key in self:
             return key

src/basilisp/lang/vector.py

@@ -30,6 +30,9 @@ def __init__(
         self._inner = wrapped
         self._meta = meta
 
+    def __bool__(self):
+        return True
+
     def __contains__(self, item):
         return item in self._inner
 

tests/basilisp/list_test.py

@@ -40,6 +40,10 @@ def test_list_slice():
     assert isinstance(llist.l(1, 2, 3)[1:], llist.List)
 
 
+def test_list_bool():
+    assert True is bool(llist.List.empty())
+
+
 def test_list_cons():
     meta = lmap.m(tag="async")
     l1 = llist.l(keyword("kw1"), meta=meta)

tests/basilisp/map_test.py

@@ -53,6 +53,10 @@ def test_assoc():
     assert lmap.map({"a": 3, "b": 2}) == m1.assoc("b", 2)
 
 
+def test_map_bool():
+    assert True is bool(lmap.Map.empty())
+
+
 def test_map_as_function():
     assert None is lmap.m()(1)
     assert None is lmap.m()("abc")

tests/basilisp/seq_test.py

@@ -78,6 +78,7 @@ def test_empty_sequence():
     assert empty.rest == empty
     assert llist.l(1) == empty.cons(1)
     assert lseq.EMPTY is empty
+    assert True is bool(lseq.sequence([]))
 
 
 def test_sequence():