Fix/minor bugs

src/danom/_result.py

@@ -264,7 +264,9 @@ def map[**P](self, func: Mappable, *args: P.args, **kwargs: P.kwargs) -> Self:
         return self
 
     def map_err[**P](self, func: Mappable, *args: P.args, **kwargs: P.kwargs) -> Err[E_co]:
-        return Err(func(self.error, *args, **kwargs))
+        return Err(
+            func(self.error, *args, **kwargs), input_args=self.input_args, traceback=self.traceback
+        )
 
     def and_then[**P](self, func: Bindable, *args: P.args, **kwargs: P.kwargs) -> Self:  # noqa: ARG002
         return self

src/danom/_stream.py

@@ -89,7 +89,7 @@ def __bool__(self) -> bool:
 
 @attrs.define(frozen=True)
 class Stream[T](_BaseStream):
-    """An immutable lazy iterator with functional operations.
+    """A lazy iterator with functional operations.
 
     Why bother?
     -----------
@@ -472,6 +472,8 @@ def par_collect(self, workers: int = 4, *, use_threads: bool = False) -> tuple[U
         if workers == -1:
             workers = (os.cpu_count() or 5) - 1
 
+        workers = max(workers, 1)
+
         executor_cls = ThreadPoolExecutor if use_threads else ProcessPoolExecutor
 
         batches = [

tests/test_stream.py

@@ -34,6 +34,9 @@ def _get_attr_collect(stream: Stream, collect_fn: str, kwargs: dict) -> tuple:
         pytest.param("collect", {}, id="simple `collect`"),
         pytest.param("par_collect", {"workers": 4}, id="`par_collect` with workers passed in"),
         pytest.param("par_collect", {"workers": -1}, id="`par_collect` with n-1 workers"),
+        pytest.param(
+            "par_collect", {"workers": 0}, id="`par_collect` with 0 workers falls back to 1 worker"
+        ),
         pytest.param("par_collect", {"use_threads": True}, id="`par_collect` with threads True"),
     ],
 )