add multi dispatch for various binary funcs

autoray/autoray.py

@@ -403,7 +403,8 @@ def import_lib_fn(backend, fn):
             full_location = ".".join([full_location] + split_fn[:-1])
             only_fn = split_fn[-1]
 
-            # try aliases for global (not function specific) modules and submodules
+            # try aliases for global (not function specific) modules and
+            # submodules:
             #     e.g. 'decimal' -> 'math'
             #     e.g. 'cupy.scipy' -> 'cupyx.scipy'
             # we don't do this if the function location has been explicitly
@@ -1325,14 +1326,22 @@ def einsum_dispatcher(*args, **_):
 register_dispatch("einsum", einsum_dispatcher)
 
 
-def tensordot_dispatcher(*args, **_):
-    """There are cases when we want to take into account both backends."""
+def binary_dispatcher(*args, **_):
+    """There are cases when we want to take into account both backends of two
+    arguments, e.g. a lazy variable and a constant array.
+    """
     return infer_backend_multi(*args[:2])
 
 
-register_dispatch("tensordot", tensordot_dispatcher)
+register_dispatch("tensordot", binary_dispatcher)
+register_dispatch("matmul", binary_dispatcher)
+register_dispatch("multiply", binary_dispatcher)
+register_dispatch("divide", binary_dispatcher)
+register_dispatch("true_divide", binary_dispatcher)
+register_dispatch("add", binary_dispatcher)
+register_dispatch("subtract", binary_dispatcher)
 
-# TODO: register other binary functions such as add, matmul etc?
+# TODO: register other binary functions?
 
 # --------------- object to act as drop-in replace for numpy ---------------- #