Add TODO & Warning for bug in Expr.replace

2 files changed, 11 insertions, 0 deletions

diff --git a/mdpoly/abc.py b/mdpoly/abc.py
index 1ceac87..618d3cd 100644
--- a/mdpoly/abc.py
+++ b/mdpoly/abc.py
@@ -73,6 +73,16 @@ class Expr(Protocol):
         It can also be used for more advanced replacements since ``old`` and
         ``new`` are free to be any expression.
         """
+        # FIXME: this doesn't work if old is something like y ** 2,
+        # TODO: Define equality on expr object
+        if not isinstance(old, Leaf):
+            import warnings
+            warnings.warn(
+                "FIXME: You are trying to replace an expression with another "
+                "expression, but this does not work yet. Currently it is only "
+                "possible to replace leaves (Variable, Constant, Parameter) with "
+                "leaves / expressions.")
+
         def replace_all(node):
             if node == old:
                 return new 
diff --git a/mdpoly/representations.py b/mdpoly/representations.py
index 802167b..da038bd 100644
--- a/mdpoly/representations.py
+++ b/mdpoly/representations.py
@@ -20,6 +20,7 @@ class HasRepr(Protocol):
         See also :py:class:`mdpoly.state.State`.
         """
 
+
 class SparseRepr(Repr):
     """ Sparse representation of polynomial. """