Fix Expression._binary, avoid creating unnecessary nodes

1 files changed, 7 insertions, 13 deletions

diff --git a/polymatrix/expression/expression.py b/polymatrix/expression/expression.py
index edb0830..3c52297 100644
--- a/polymatrix/expression/expression.py
+++ b/polymatrix/expression/expression.py
@@ -117,31 +117,25 @@ class Expression(ExpressionBaseMixin, ABC):
     def _binary(op, left, right):
         stack = get_stack_lines()
 
-        if isinstance(left, Expression):
-            right = polymatrix.expression.init.init_from_expr_or_none(right)
+        if isinstance(left, Expression) and isinstance(right, Expression):
+            return left.copy(underlying=op(left.underlying, right.underlying, stack))
 
-            # delegate to upper level
+        elif isinstance(left, Expression):
+            right = polymatrix.expression.init.init_from_expr_or_none(right)
 
-            # NP: what is upper level? Class inherits from ABC and base class,
-            # NP: neither has binary operators, also NotImplemented IIRC is only for __lt__
-            # NP: and other comparison methods and not for overloadings like __add__
             if right is None:
                 return NotImplemented
 
-            return left.copy(
-                underlying=op(left, right, stack),
-            )
+            return left.copy(underlying=op(left.underlying, right, stack))
 
+        # else right is an Expression
         else:
             left = polymatrix.expression.init.init_from_expr_or_none(left)
 
-            # delegate to upper level
             if left is None:
                 return NotImplemented
 
-            return right.copy(
-                underlying=op(left, right, stack),
-            )
+            return right.copy( underlying=op(left, right.underlying, stack))
 
     def cache(self) -> "Expression":
         return self.copy(