remove types 'positive', 'negative', and 'zero'

  - These fine value-dependent distinctions should be made at runtime, not
    during type checking.
  - Fix a small bug in the algorithm to find a converter given two types.

1 files changed, 13 insertions, 30 deletions

diff --git a/TurtleArt/tatype.py b/TurtleArt/tatype.py
index 3fa7a83..14f1c9e 100644
--- a/TurtleArt/tatype.py
+++ b/TurtleArt/tatype.py
@@ -57,12 +57,10 @@ TYPE_CHAR = Type('char', 1)
 TYPE_COLOR = Type('color', 2)
 TYPE_FLOAT = Type('float', 3)
 TYPE_INT = Type('int', 4)
-TYPE_NEGATIVE = Type('negative', 5)
-TYPE_NUMBER = Type('number', 6)
+TYPE_NUMBER = Type('number', 6)  # shortcut to avoid a TypeDisjunction between
+# TYPE_FLOAT and TYPE_INT
 TYPE_NUMERIC_STRING = Type('numeric string', 7)
-TYPE_POSITIVE = Type('positive', 8)
 TYPE_STRING = Type('string', 9)
-TYPE_ZERO = Type('zero', 10)
 # TODO add list types
 
 
@@ -71,13 +69,10 @@ def get_type(x):
     and a boolean indicating whether x is an AST. If the type cannot be
     determined, return TYPE_OBJECT as the type. """
     # non-AST types
-    if isinstance(x, (float, int, long)):
-        if x > 0:
-            return (TYPE_POSITIVE, False)
-        elif x == 0:
-            return (TYPE_ZERO, False)
-        else:
-            return (TYPE_NEGATIVE, False)
+    if isinstance(x, (int, long)):
+        return (TYPE_INT, False)
+    elif isinstance(x, float):
+        return (TYPE_FLOAT, False)
     elif isinstance(x, basestring):
         if len(x) == 1:
             return (TYPE_CHAR, False)
@@ -107,8 +102,10 @@ def get_type(x):
             return (get_type(value)[0], True)
     elif isinstance(x, ast.Call):
         if isinstance(x.func, ast.Name):
-            if x.func.id in ('float', 'int'):
-                return (x.func.__name__, True)
+            if x.func.id == 'float':
+                return (TYPE_FLOAT, True)
+            if x.func.id == 'int':
+                return (TYPE_INT, True)
             elif x.func.id in ('repr', 'str', 'unicode'):
                 return (TYPE_STRING, True)
 
@@ -140,7 +137,6 @@ TYPE_CONVERTERS = {
     # converting A -> C must yield the same result as converting A -> B -> C.
     # TYPE_OBJECT is the supertype of everything.
     TYPE_CHAR: {
-        TYPE_POSITIVE: ord,  # ignore the zero byte, chr(0)
         TYPE_STRING: identity},
     TYPE_COLOR: {
         TYPE_FLOAT: float,
@@ -155,26 +151,13 @@ TYPE_CONVERTERS = {
         TYPE_FLOAT: float,
         TYPE_NUMBER: identity,
         TYPE_STRING: str},
-    TYPE_NEGATIVE: {
-        TYPE_FLOAT: float,
-        TYPE_INT: int,
-        TYPE_NUMBER: identity,
-        TYPE_STRING: str},
     TYPE_NUMBER: {
-        TYPE_STRING: str},
-    TYPE_NUMERIC_STRING: {
-        TYPE_FLOAT: float,
-        TYPE_STRING: identity},
-    TYPE_POSITIVE: {
         TYPE_FLOAT: float,
         TYPE_INT: int,
-        TYPE_NUMBER: identity,
         TYPE_STRING: str},
-    TYPE_ZERO: {
+    TYPE_NUMERIC_STRING: {
         TYPE_FLOAT: float,
-        TYPE_INT: int,
-        TYPE_NUMBER: identity,
-        TYPE_STRING: str}
+        TYPE_STRING: identity}
 }
 
 
@@ -251,7 +234,7 @@ def get_converter(old_type, new_type):
         # form the transitive closure of all types that old_type can be
         # converted to, and look for new_type there
         backtrace = converters_from_old.copy()
-        new_backtrace = backtrace
+        new_backtrace = backtrace.copy()
         break_all = False
         while True:
             newest_backtrace = {}