Enabled parsing for division expressions

However, true support is currently blocked on #19.

cozy/parse.py

@@ -61,6 +61,7 @@
     ("PLUS", "+"),
     ("MINUS", "-"),
     ("TIMES", "*"),
+    ("DIVIDE", "/"),
     ("QUESTION", "?"),
     ("COLON", ":"),
     ("SEMICOLON", ";"),
@@ -326,6 +327,7 @@ def p_exp(p):
                | exp OP_MINUS exp
                | OP_MINUS exp
                | exp OP_TIMES exp
+               | exp OP_DIVIDE exp
                | exp OP_QUESTION exp OP_COLON exp
                | exp OP_DOT NUM
                | exp OP_DOT WORD

cozy/typecheck.py

@@ -429,6 +429,15 @@ def visit_EBinOp(self, e):
             else:
                 e.type = DEFAULT_TYPE
                 self.report_err(e, "cannot multiply {} and {}".format(pprint(e.e1.type), pprint(e.e2.type)))
+        elif e.op == "/":
+            e.type = FLOAT
+            if not (e.e1.type is DEFAULT_TYPE or e.e1.type == FLOAT):
+                self.report_err(e, "division is only legal on floats; left-hand side {} has type {}".format(pprint(e.e1), pprint(e.e1.type)))
+            if not (e.e2.type is DEFAULT_TYPE or e.e2.type == FLOAT):
+                self.report_err(e, "division is only legal on floats; right-hand side {} has type {}".format(pprint(e.e2), pprint(e.e2.type)))
+            self.report_err(e,
+                "Division is currently unsupported since it is a partial function (x/0 is undefined)."
+                + "  See https://github.com/CozySynthesizer/cozy/issues/19 for more information.")
         else:
             raise NotImplementedError(e.op)