feat(py): ComposablePass protocol and ComposedPass for hugr-py

hugr-py/src/hugr/hugr/__init__.py

@@ -1,6 +1,7 @@
 """The main HUGR structure."""
 
 from .base import Hugr, NodeData
+from .composable_pass import ComposablePass
 from .node_port import (
     Direction,
     InPort,
@@ -10,11 +11,12 @@
 )
 
 __all__ = [
-    "Hugr",
-    "NodeData",
+    "ComposablePass",
     "Direction",
+    "Hugr",
     "InPort",
-    "Wire",
-    "OutPort",
     "Node",
+    "NodeData",
+    "OutPort",
+    "Wire",
 ]

hugr-py/src/hugr/hugr/composable_pass.py

@@ -0,0 +1,24 @@
+"""A Protocol for a composable pass."""
+
+from typing import Protocol
+
+from typing_extensions import Self
+
+from hugr.hugr.base import Hugr
+from hugr.hugr.node_port import Node
+
+
+class ComposablePass(Protocol):
+    """A Protocol which represents a composable Hugr transformation."""
+
+    def __call__(self, hugr: Hugr) -> None: ...
+
+    def then(self, other: Self) -> Self: ...
+
+    def with_entrypoint(self, entrypoint: Node) -> Self: ...
+
+    @property
+    def is_global(self) -> bool: ...
+
+    @property
+    def is_recursive(self) -> bool: ...