From b710b8bbc67c327f2c678325bf258785e5cc4ed2 Mon Sep 17 00:00:00 2001
From: Caleb Donovick <donovick@cs.stanford.edu>
Date: Fri, 2 Aug 2019 10:26:41 -0700
Subject: [PATCH 1/2] Add tag decorator

---
 peak/bitfield.py  | 16 ++++++++++++++++
 tests/test_tag.py | 31 +++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 tests/test_tag.py

diff --git a/peak/bitfield.py b/peak/bitfield.py
index 7f1ed2a3..9788c0cd 100644
--- a/peak/bitfield.py
+++ b/peak/bitfield.py
@@ -1,6 +1,22 @@
+import typing as tp
+
 from hwtypes.adt import Enum, Sum, Product
 from hwtypes import AbstractBitVector
 
+def tag(tags: tp.Mapping[type, int]):
+    def wrapper(sum: Sum):
+        if not isinstance(sum, Sum):
+            raise TypeError('tag can only be applied Sum')
+        if tags.keys() != sum.fields:
+            raise ValueError('tag must specificy an Option for each Sum option')
+        if not all(isinstance(t, int) for t in tags.values()):
+            raise TypeError('tags must be int')
+
+        setattr(sum, 'tags', tags)
+        return sum
+    return wrapper
+
+
 def bitfield(i):
     def wrap(klass):
         klass.bitfield = i
diff --git a/tests/test_tag.py b/tests/test_tag.py
new file mode 100644
index 00000000..dc4d1c22
--- /dev/null
+++ b/tests/test_tag.py
@@ -0,0 +1,31 @@
+import pytest
+from hwtypes.adt import Sum
+
+from peak.bitfield import tag
+
+def test_tag():
+    @tag({int : 0, str : 1})
+    class S(Sum[int ,str]): pass
+
+    assert S.tags[int] == 0
+    assert S.tags[str] == 1
+
+    with pytest.raises(TypeError):
+        @tag()
+        class S: pass
+
+    with pytest.raises(ValueError):
+        @tag({int : 0, str : 1, object : 2})
+        class S(Sum[int ,str]): pass
+
+    with pytest.raises(ValueError):
+        @tag({int : 0})
+        class S(Sum[int ,str]): pass
+
+    with pytest.raises(TypeError):
+        @tag({int : 'a', str : 1})
+        class S(Sum[int ,str]): pass
+
+
+
+

From a09d27f42cca0029b1b689004892e823a61a99f8 Mon Sep 17 00:00:00 2001
From: Caleb Donovick <donovick@cs.stanford.edu>
Date: Fri, 2 Aug 2019 10:29:09 -0700
Subject: [PATCH 2/2] mend

---
 peak/bitfield.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/peak/bitfield.py b/peak/bitfield.py
index 9788c0cd..c866ebaa 100644
--- a/peak/bitfield.py
+++ b/peak/bitfield.py
@@ -5,7 +5,7 @@
 
 def tag(tags: tp.Mapping[type, int]):
     def wrapper(sum: Sum):
-        if not isinstance(sum, Sum):
+        if not issubclass(sum, Sum):
             raise TypeError('tag can only be applied Sum')
         if tags.keys() != sum.fields:
             raise ValueError('tag must specificy an Option for each Sum option')