Added Result or_else methods (#226)

expression/core/result.py

@@ -180,6 +180,14 @@ def swap(self) -> Result[_TError, _TSource]:
             case Result(error=error):
                 return Result(ok=error)
 
+    def or_else(self, other: Result[_TSource, _TError]) -> Result[_TSource, _TError]:
+        """Return the result if it is Ok, otherwise return the other result."""
+        return self if self.is_ok() else other
+
+    def or_else_with(self, other: Callable[[_TError], Result[_TSource, _TError]]) -> Result[_TSource, _TError]:
+        """Return the result if it is Ok, otherwise return the result of the other function."""
+        return self if self.is_ok() else other(self.error)
+
     def to_option(self) -> Option[_TSource]:
         """Convert result to an option."""
         match self:

tests/test_result.py

@@ -523,3 +523,50 @@ def test_result_swap_with_error():
     error: Result[str, int] = Error(1)
     xs = result.swap(error)
     assert xs == Ok(1)
+
+def test_ok_or_else_ok():
+    xs: Result[int, str] = Ok(42)
+    ys = xs.or_else(Ok(0))
+    assert ys == Ok(42)
+
+
+def test_ok_or_else_error():
+    xs: Result[int, str] = Ok(42)
+    ys = xs.or_else(Error("new error"))
+    assert ys == Ok(42)
+
+
+def test_error_or_else_ok():
+    xs: Result[int, str] = Error("original error")
+    ys = xs.or_else(Ok(0))
+    assert ys == Ok(0)
+
+
+def test_error_or_else_error():
+    xs: Result[int, str] = Error("original error")
+    ys = xs.or_else(Error("new error"))
+    assert ys == Error("new error")
+
+
+def test_ok_or_else_with_ok():
+    xs: Result[str, str] = Ok("good")
+    ys = xs.or_else_with(lambda error: Ok(f"new error from {error}"))
+    assert ys == Ok("good")
+
+
+def test_ok_or_else_with_error():
+    xs: Result[str, str] = Ok("good")
+    ys = xs.or_else_with(lambda error: Ok(f"new error from {error}"))
+    assert ys == Ok("good")
+
+
+def test_error_or_else_with_ok():
+    xs: Result[str, str] = Error("original error")
+    ys = xs.or_else_with(lambda error: Ok(f"fixed {error}"))
+    assert ys == Ok("fixed original error")
+
+
+def test_error_or_else_with_error():
+    xs: Result[str, str] = Error("original error")
+    ys = xs.or_else_with(lambda error: Error(f"new error from {error}"))
+    assert ys == Error("new error from original error")