From 484c6e97f1d62e99b82c63823ad37814afb1b466 Mon Sep 17 00:00:00 2001
From: Jan Verbeek <jan.verbeek@posteo.nl>
Date: Tue, 11 Jun 2019 18:33:07 +0200
Subject: [PATCH] Support Python 3.6

---
 .travis.yml     |  1 +
 README.md       |  2 +-
 nnf/__init__.py | 22 ++++++++++------------
 setup.py        |  3 ++-
 tox.ini         |  2 +-
 5 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index 8852eb7..5559f51 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,6 +3,7 @@ dist: xenial
 language: python
 
 python:
+  - "3.6"
   - "3.7"
 
 install:
diff --git a/README.md b/README.md
index fd75e9a..46cd708 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ This package takes much of its data model and terminology from
 pip install nnf
 ```
 
-Only Python 3.7 or higher is currently supported.
+At least Python 3.6 is required.
 
 # Serialization
 
diff --git a/nnf/__init__.py b/nnf/__init__.py
index 78b16d5..e42c669 100644
--- a/nnf/__init__.py
+++ b/nnf/__init__.py
@@ -12,8 +12,6 @@
 # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 # OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
-from __future__ import annotations
-
 import functools
 import itertools
 import typing as t
@@ -57,15 +55,15 @@ def all_models(names: t.Collection[Name]) -> t.Iterator[Model]:
 class NNF:
     """Base class for all NNF sentences."""
 
-    def __and__(self, other: NNF) -> NNF:
+    def __and__(self, other: 'NNF') -> 'NNF':
         """And({self, other})"""
         return And({self, other})
 
-    def __or__(self, other: NNF) -> NNF:
+    def __or__(self, other: 'NNF') -> 'NNF':
         """Or({self, other})"""
         return Or({self, other})
 
-    def walk(self) -> t.Iterator[NNF]:
+    def walk(self) -> t.Iterator['NNF']:
         """Yield all nodes in the sentence, depth-first.
 
         Nodes that appear multiple times are yielded only once.
@@ -256,7 +254,7 @@ def models(self, decomposable: _Tristate = None) -> t.Iterator[Model]:
                 if self.satisfied_by(model):
                     yield model
 
-    def contradicts(self, other: NNF) -> bool:
+    def contradicts(self, other: 'NNF') -> bool:
         """There is no set of values that satisfies both sentences."""
         if self.vars() != other.vars():
             raise ValueError("Sentences mention different variables")
@@ -267,7 +265,7 @@ def contradicts(self, other: NNF) -> bool:
                 return False
         return True
 
-    def to_MODS(self) -> NNF:
+    def to_MODS(self) -> 'NNF':
         """Convert the sentence to a MODS sentence."""
         return Or(And(Var(name, val)
                       for name, val in model.items())
@@ -295,7 +293,7 @@ def to_model(self) -> Model:
 
         return model
 
-    def condition(self, model: Model) -> NNF:
+    def condition(self, model: Model) -> 'NNF':
         """Fill in all the values in the dictionary."""
         @memoize
         def cond(node: NNF) -> NNF:
@@ -315,7 +313,7 @@ def cond(node: NNF) -> NNF:
 
         return cond(self)
 
-    def simplify(self) -> NNF:
+    def simplify(self) -> 'NNF':
         """Apply the following transformations to make the sentence simpler:
 
         - If an And node has `false` as a child, replace it by `false`
@@ -367,7 +365,7 @@ def simple(node: NNF) -> NNF:
 
         return simple(self)
 
-    def deduplicate(self) -> NNF:
+    def deduplicate(self) -> 'NNF':
         """Return a copy of the sentence without any duplicate objects.
 
         If a node has multiple parents, it's possible for it to be
@@ -464,7 +462,7 @@ def name(node: NNF) -> int:
 
     def transform(
             self,
-            func: t.Callable[[t.Callable[[NNF], T], NNF], T]
+            func: t.Callable[[t.Callable[['NNF'], T], 'NNF'], T]
     ) -> T:
         """A helper function to apply a transformation with memoization.
 
@@ -625,7 +623,7 @@ def __repr__(self) -> str:
             base = f"{self.__class__.__name__}({self.name!r})"
             return base if self.true else f"~{base}"
 
-    def __invert__(self) -> Var:
+    def __invert__(self) -> 'Var':
         return Var(self.name, not self.true)
 
 
diff --git a/setup.py b/setup.py
index f635ae0..ffd0804 100644
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,7 @@
 
 setuptools.setup(
     name="nnf",
-    version="0.0.2",
+    version="0.0.3",
     author="Jan Verbeek",
     author_email="jan.verbeek@posteo.nl",
     description="Manipulate NNF (Negation Normal Form) logical sentences",
@@ -21,6 +21,7 @@
         "Development Status :: 2 - Pre-Alpha",
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3 :: Only",
         "License :: OSI Approved :: ISC License (ISCL)",
diff --git a/tox.ini b/tox.ini
index b035ed1..809706c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py37
+envlist = py36, py37
 
 [testenv]
 deps =