correct README statement about recursive terms

BetaNormalisingVisitor can not produce cycles
because it does not modify terms, preventing them
from referencing terms available after their construction.

Author: Deric-W

README.md

@@ -15,13 +15,9 @@ use predefined ones from the `terms` subpackage.
 
 This package is intended to be used for educational purposes and is not optimized for speed.
 
-Furthermore, it expects all terms to be finite, which means the absense of cycles.
+Furthermore, it expects all terms to be finite, which means the absence of cycles.
 
-This results in the Visitor for term normalisation included in this package (`BetaNormalisingVisitor`)
-having problems when handling terms which are passed a reference to themselves during evaluation,
-which is the case for all recursive functions.
-
-`RecursionError` may be raised if the visitors get passed an infinite term.
+`RecursionError` may be raised if the visitors get passed an infinite term or the evaluation is too complex.
 
 ## Requirements
 

lambda_calculus/__init__.py

@@ -4,7 +4,7 @@
 
 from .terms import Variable, Abstraction, Application
 
-__version__ = "2.2.0"
+__version__ = "2.2.1"
 __author__  = "Eric Niklas Wolf"
 __email__   = "[email protected]"
 __all__ = (

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "lambda_calculus"
-version = "2.2.0"
+version = "2.2.1"
 description = "Implementation of the Lambda calculus"
 requires-python = ">=3.10"
 keywords = []

tests/visitors/test_normalisation.py

@@ -145,3 +145,14 @@ def test_skip_intermediate(self) -> None:
             ),
             Variable("z")
         )
+
+    def test_self_argument(self) -> None:
+        """test behavior when applying a term to itself"""
+        term = Variable("a").apply_to(Variable("b")).abstract("a")
+        term_copy = Variable("a").apply_to(Variable("b")).abstract("a")
+        self.assertEqual(
+            self.visitor.skip_intermediate(term.apply_to(term)),
+            Variable("b").apply_to(Variable("b"))
+        )
+        # prevent original for being modified
+        self.assertEqual(term, term_copy)