Initial Commit

tail_recurse/__init__.py

@@ -0,0 +1,40 @@
+"""
+Python Decorator that enables tail call
+optimization through Exception Trampolines.
+"""
+from dataclasses import dataclass, field
+from typing import Any, Dict, List
+import functools
+import inspect
+
+@dataclass
+class TailRecurseException(Exception):
+    """Exception to enable tail call recursion."""
+    args: List[Any] = field(default_factory=list)
+    kwargs: Dict[Any, Any] = field(default_factory=dict)
+
+def tail_call(func):
+    """
+    Decorator that performs tail call optimization.
+
+    Notes
+    =====
+    Works by throwing an exception to exit the stack
+    when the function sees itself as its grandparent in
+    the stack trace. It then calls itself with its new
+    arguments.
+    """
+    @functools.wraps(func)
+    def recurse(*args, **kwargs):
+        frame = inspect.currentframe()
+        if frame.f_back is not None \
+           and frame.f_back.f_back is not None \
+           and frame.f_back.f_back.f_code == frame.f_code:
+            raise TailRecurseException(args, kwargs)
+        while True:
+            try:
+                return func(*args, **kwargs)
+            except TailRecurseException as exception:
+                args = exception.args
+                kwargs = exception.kwargs
+    return recurse