better handling for TATypeErrors coming from the type system

1 files changed, 28 insertions, 15 deletions

diff --git a/TurtleArt/tatype.py b/TurtleArt/tatype.py
index d4fec2b..6b0acd6 100644
--- a/TurtleArt/tatype.py
+++ b/TurtleArt/tatype.py
@@ -195,22 +195,34 @@ def get_call_ast(func_name, args=None, keywords=None):
 class TATypeError(BaseException):
     """ TypeError with the types from the hierarchy, not with Python types """
 
-    def __init__(self, message, type1=None, type2=None):
-        """ message -- the error message (type1 and type2 are inserted
-            automatically iff message contains '%s' for them) """
+    def __init__(self, bad_value, bad_type=None, req_type=None, message=''):
+        """ bad_value -- the mis-typed value that caused the error
+        bad_type -- the type of the bad_value
+        req_type -- the type that the value was expected to have
+        message -- short statement about the cause of the error. It is
+            not shown to the user, but may appear in debugging output. """
+        self.bad_value = bad_value
+        self.bad_type = bad_type
+        self.req_type = req_type
         self.message = message
-        self.type1 = type1
-        self.type2 = type2
 
     def __str__(self):
-        num = self.message.count('%s')
-        if num == 2:
-            msg = self.message % (self.type1, self.type2)
-        elif num == 1:
-            msg = self.message % (self.type1)
-        else:
-            msg = self.message
-        return "TA TypeError: " + msg
+        msg = []
+        if self.message:
+            msg.append(self.message)
+            msg.append(" (")
+        msg.append("bad value: ")
+        msg.append(repr(self.bad_value))
+        if self.bad_type is not None:
+            msg.append(", bad type: ")
+            msg.append(repr(self.bad_type))
+        if self.req_type is not None:
+            msg.append(", req type: ")
+            msg.append(repr(self.req_type))
+        if self.message:
+            msg.append(")")
+        return "".join(msg)
+    __repr__ = __str__
 
 
 def get_converter(old_type, new_type):
@@ -285,8 +297,9 @@ def convert(x, new_type, old_type=None, converter=None):
         converter = get_converter(old_type, new_type)
         if converter is None:
             # no converter available
-            raise TATypeError("type %s cannot be converted to type %s"
-                                  % (repr(old_type), repr(new_type)))
+            raise TATypeError(bad_value=x, bad_type=old_type,
+                              req_type=new_type, message=("found no converter"
+                                  " for this type combination"))
 
     def _apply_converter(converter, y):
         if is_an_ast: