Changed assiociativity for derivatives/integrals to left.

TODO

@@ -111,3 +111,5 @@ Division of 0 by 1 reduces to 0.
  - MESSAGES needs to be expanded.
 
  - Use pretty-print for expressions in hint messages.
+
+ - Parser: add unit tests for operator associativity (derivatives/integrals).

src/parser.py

@@ -86,7 +86,7 @@ class Parser(BisonParser):
     # ------------------------------
     precedences = (
         ('left', ('COMMA', )),
-        ('right', ('INTEGRAL', 'DERIVATIVE')),
+        ('left', ('INTEGRAL', 'DERIVATIVE')),
         ('left', ('OR', )),
         ('left', ('AND', )),
         ('left', ('EQ', )),