From 38b8c1838f9e6485b9e3363152f8fd3247c99193 Mon Sep 17 00:00:00 2001
From: Marcell Vazquez-Chanlatte <mvc@linux.com>
Date: Mon, 27 Nov 2017 13:10:56 -0800
Subject: [PATCH] support discretizing top and bot

---
 stl/test_utils.py | 12 ++++++++++++
 stl/utils.py      |  2 +-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/stl/test_utils.py b/stl/test_utils.py
index a8a024c..b05e95c 100644
--- a/stl/test_utils.py
+++ b/stl/test_utils.py
@@ -94,6 +94,18 @@ def test_discretize():
     assert phi2 == stl.parse(
         '(~((X(A)) ∨ (X(X(A))))) ∧ (~((X(X(A))) ∨ (X(X(X(A))))))')
 
+    phi = stl.TOP
+    assert stl.utils.is_discretizable(phi, dt)
+    phi2 = stl.utils.discretize(phi, dt)
+    phi3 = stl.utils.discretize(phi2, dt)
+    assert phi2 == phi3
+
+    phi = stl.BOT
+    assert stl.utils.is_discretizable(phi, dt)
+    phi2 = stl.utils.discretize(phi, dt)
+    phi3 = stl.utils.discretize(phi2, dt)
+    assert phi2 == phi3
+
 
 def test_scope():
     dt = 0.3
diff --git a/stl/utils.py b/stl/utils.py
index 341fe56..32d933f 100644
--- a/stl/utils.py
+++ b/stl/utils.py
@@ -128,7 +128,7 @@ def discretize(phi, dt, distribute=False):
 
 
 def _discretize(phi, dt):
-    if isinstance(phi, (LinEq, AtomicPred)):
+    if isinstance(phi, (LinEq, AtomicPred, _Top, _Bot)):
         return phi
 
     children = tuple(_discretize(arg, dt) for arg in phi.children)