add arithmetic.ISZERO term

Author: Deric-W

lambda_calculus/__init__.py

@@ -4,7 +4,7 @@
 
 from .terms import Variable, Abstraction, Application
 
-__version__ = "2.0.1"
+__version__ = "2.1.0"
 __author__  = "Eric Niklas Wolf"
 __email__   = "[email protected]"
 __all__ = (

lambda_calculus/terms/arithmetic.py

@@ -3,8 +3,10 @@
 """Implementations of natural numbers and arithmetic operators"""
 
 from . import Term, Variable, Abstraction, Application
+from .logic import TRUE, FALSE
 
 __all__ = (
+    "ISZERO",
     "SUCCESSOR",
     "PREDECESSOR",
     "ADD",
@@ -14,6 +16,8 @@
     "number"
 )
 
+ISZERO = Variable("n").apply_to(FALSE.abstract("x"), TRUE).abstract("n")
+
 SUCCESSOR = Abstraction.curried(
     ("n", "f", "x"),
     Application(

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "lambda_calculus"
-version = "2.0.1"
+version = "2.1.0"
 description = "Implementation of the Lambda calculus"
 requires-python = ">=3.10"
 keywords = []

tests/terms/test_arithmetic.py

@@ -4,7 +4,7 @@
 
 from unittest import TestCase
 from lambda_calculus.visitors.normalisation import BetaNormalisingVisitor
-from lambda_calculus.terms import Application, arithmetic
+from lambda_calculus.terms import Application, arithmetic, logic
 
 
 class OrderingTest(TestCase):
@@ -16,6 +16,21 @@ def setUp(self) -> None:
         """create a visitor"""
         self.visitor = BetaNormalisingVisitor()
 
+    def test_iszero(self) -> None:
+        """test iszero term"""
+        self.assertEqual(
+            self.visitor.skip_intermediate(
+                arithmetic.ISZERO.apply_to(arithmetic.number(0))
+            ),
+            logic.TRUE
+        )
+        self.assertEqual(
+            self.visitor.skip_intermediate(
+                arithmetic.ISZERO.apply_to(arithmetic.number(1))
+            ),
+            logic.FALSE
+        )
+
     def test_successor(self) -> None:
         """test successor term"""
         self.assertEqual(