diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index 01b7ff61..8adae48d 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -37,15 +37,15 @@ jobs:
       - name: Deploy docs
         run: |
           mkdocs gh-deploy --clean --force
-        if: success() && github.ref == 'refs/heads/master'
+        # if: success() && github.ref == 'refs/heads/master'
 
   fix-index:
     needs: docs
     runs-on: ubuntu-latest
-    if: github.ref == 'refs/heads/master'
+    # if: github.ref == 'refs/heads/master'
     strategy:
       matrix:
-        python-version: [3.8]
+        python-version: [3.9]
     steps:
       - uses: actions/checkout@v2
         with:
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d41295df..7e71eca1 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -55,7 +55,7 @@ repos:
         files: ^tests/.+$|^datar/.+$
     -   id: notebooks
         name: Executing all notebooks
-        entry: jupyter nbconvert --to notebook --execute
+        entry: jupyter nbconvert --output-dir /tmp --to notebook --execute
         language: system
         pass_filenames: true
         files: ^docs/.+\.ipynb$
diff --git a/datar/__init__.py b/datar/__init__.py
index 84410305..3355ef9f 100644
--- a/datar/__init__.py
+++ b/datar/__init__.py
@@ -7,7 +7,7 @@
 from .core.defaults import f
 
 __all__ = ('f', 'get_versions')
-__version__ = "0.5.0"
+__version__ = "0.5.1"
 
 def get_versions(
     prnt: bool = True
diff --git a/datar/base/__init__.py b/datar/base/__init__.py
index 2f92c3a7..2e4b0c67 100644
--- a/datar/base/__init__.py
+++ b/datar/base/__init__.py
@@ -40,7 +40,7 @@
 from .complex import arg, as_complex, conj, im, is_complex, mod, re as re_
 from .constants import LETTERS, letters, month_abb, month_name, pi
 from .cum import cummax, cummin, cumprod, cumsum
-from .date import as_date
+from .date import as_date, as_pd_date
 from .factor import (
     as_categorical,
     as_factor,
@@ -125,6 +125,7 @@
     startswith,
     endswith,
     strtoi,
+    trimws,
     chartr,
     tolower,
     toupper,
diff --git a/datar/base/date.py b/datar/base/date.py
index 1b62ae53..15c1f3c0 100644
--- a/datar/base/date.py
+++ b/datar/base/date.py
@@ -2,16 +2,21 @@
 
 import datetime
 import functools
-from typing import Any, Union, List, Iterable
+from typing import TYPE_CHECKING, Any, Iterable, List, Union
 
 import numpy
-from pandas import Series, DataFrame
+import pandas
+from pandas import DataFrame, Series
 from pipda import register_func
 
-from ..core.types import IntType, is_scalar_int, is_scalar
 from ..core.contexts import Context
+from ..core.types import IntType, is_scalar, is_scalar_int
 from .na import NA
 
+if TYPE_CHECKING:  # pragma: no cover
+    # pylint: disable=ungrouped-imports
+    from pandas import DatetimeIndex, Timestamp
+
 # pylint: disable=invalid-name
 # pylint: disable=redefined-builtin
 
@@ -144,7 +149,7 @@ def as_date(
     optional: bool = False,
     tz: Union[IntType, datetime.timedelta] = 0,
     origin: Any = None,
-) -> Iterable[datetime.date]:
+) -> Union[Series, "Timestamp", "DatetimeIndex"]:
     """Convert an object to a datetime.date object
 
     See: https://rdrr.io/r/base/as.Date.html
@@ -155,6 +160,11 @@ def as_date(
             the first non-NA element, and give an error if none works.
             Otherwise, the processing is via strptime
         try_formats: vector of format strings to try if format is not specified.
+            Default formats to try:
+            "%Y-%m-%d"
+            "%Y/%m/%d"
+            "%Y-%m-%d %H:%M:%S"
+            "%Y/%m/%d %H:%M:%S"
         optional: indicating to return NA (instead of signalling an error)
             if the format guessing does not succeed.
         origin: a datetime.date/datetime object, or something which can be
@@ -168,7 +178,7 @@ def as_date(
     if not isinstance(x, Series):
         x = Series([x]) if is_scalar(x) else Series(x)
 
-    return x.transform(
+    out = x.transform(
         _as_date_dummy,
         format=format,
         try_formats=try_formats,
@@ -176,3 +186,25 @@ def as_date(
         tz=tz,
         origin=origin,
     )
+    return pandas.to_datetime(out)
+
+@register_func(None, context=Context.EVAL)
+def as_pd_date(
+    arg: Union[int, str, float, datetime.datetime, Iterable],
+    *args: Any,
+    **kwargs: Any,
+) -> Union[Series, "Timestamp", "DatetimeIndex"]:
+    """Alias of pandas.to_datetime(), but registered as a function
+    so that it can be used in verbs.
+
+    See https://pandas.pydata.org/docs/reference/api/pandas.to_datetime.html
+
+    Args:
+        arg: The argument to be converted to datetime
+        *args: and
+        **kwargs: Other arguments passing to `pandas.to_datetime()`
+
+    Returns:
+        Converted datetime
+    """
+    return pandas.to_datetime(arg, *args, **kwargs)
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 09f7cf3f..4d6ac031 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -1,3 +1,9 @@
+## 0.5.1
+- Add documentation about "blind" environment (#45, #54, #55)
+- Change `base.as_date()` to return pandas datetime types instead python datetime types (#56)
+- Add `base.as_pd_date()` to be an alias of `pandas.to_datetime()` (#56)
+- Expose `trimws` to `datar.all` (#58)
+
 ## 0.5.0
 
 Added:
diff --git a/docs/caveats/blind.md b/docs/caveats/blind.md
new file mode 100644
index 00000000..e0886c8f
--- /dev/null
+++ b/docs/caveats/blind.md
@@ -0,0 +1,89 @@
+
+Related issues: [GH#45][1] [GH#54][2] [GH#55][3]
+
+## Why?
+To make `datar` in both regular calling and piping calling for verbs:
+
+```python
+# regular calling
+num_rows = nrow(df)
+
+# piping calling
+num_rows = df >> nrow()
+```
+
+we need the source code available to detect the AST node, especially the piping sign (`ast.BinOp(op=ast.RShift)`), so we can preserve the slot of the first argument for the data to pipe in.
+
+However, the source code is not always avaiable at runtime (i.e. raw python REPL, `exec()`), or the there could be some environment that modifies the AST tree (`assert` from `pytest`). We call those environments "blind".
+
+A quick example to simulate this siutation:
+
+```python
+>>> from datar.all import *
+>>> df = tibble(a="a")
+>>> df >> mutate(A=f.a.str.upper())
+         a        A
+  <object> <object>
+0        a        A
+>>> source = "df >> mutate(A=f.a.str.upper())"
+>>> exec(source)
+/path/to/site-packages/pipda/utils.py:161: UserWarning: Failed to fet
+ch the node calling the function, call it with the original function.
+  warnings.warn(
+Traceback (most recent call last):
+  ...
+```
+
+## Solutions
+
+- Try switching to a REPL that maintains the source code (`ipython` instead of raw python REPL, for example)
+- Save the code into a file, and run that script with python interpreter
+- Stick with the regular calling:
+
+    ```python
+    >>> source = "df2 = mutate(df, A=f.a.str.upper())"
+    >>> exec(source)  # you still get a warning, but the code works
+    /home/pwwang/miniconda3/lib/python3.9/site-packages/pipda/utils.py:161: UserWarning: Failed to fet
+    ch the node calling the function, call it with the original function.
+    warnings.warn(
+    >>> df2
+            a        A
+    <object> <object>
+    0        a        A
+    ```
+
+- Stick with the piping calling:
+
+    ```python
+    >>> from pipda import options
+    >>> options.assume_all_piping = True
+    >>> source = "df2 = df >> mutate(A=f.a.str.upper())"
+    >>> exec(source)  # no warnings, we know we don't need the AST node anymore
+    >>> df2
+            a        A
+    <object> <object>
+    0        a        A
+    ```
+
+    !!! Note
+
+        Whichever calling mode you are sticking with, you have to stick with it for all verbs, even for those simple ones (i.e. `dim()`, `nrow()`, etc)
+
+    !!! Tip
+
+        If you wonder whether a python function is registered as a verb or a plain function:
+
+        ```python
+        >>> mutate.__pipda__
+        'Verb'
+        >>> nrow.__pipda__
+        'Verb'
+        >>> as_integer.__pipda__
+        'PlainFunction'
+        ```
+
+
+
+[1]: https://github.com/pwwang/datar/issues/45
+[2]: https://github.com/pwwang/datar/issues/54
+[3]: https://github.com/pwwang/datar/issues/55
diff --git a/docs/reference-maps/base.md b/docs/reference-maps/base.md
index b2c1107e..394d9c7d 100644
--- a/docs/reference-maps/base.md
+++ b/docs/reference-maps/base.md
@@ -109,6 +109,7 @@
 |API|Description|Notebook example|
 |---|---|---:|
 |[`as_date`][41]|Cast data to date|[:material-notebook:][4]|
+|[**`as_pd_date`**][150]|Alias of `pandas.to_datetime()`||
 
 ### Factor data
 
@@ -220,6 +221,7 @@
 |[`chartr`][133]|Replace characters in strings||
 |[`tolower`][134]|Transform strings to lower case||
 |[`toupper`][135]|Transform strings to upper case||
+|[`trimws`][149]|Remove leading and/or trailing whitespace from character strings.||
 
 ### Table
 
@@ -430,3 +432,5 @@
 [146]: ../../api/datar.base.table/#datar.base.table.tabulate
 [147]: ../../api/datar.base.verbs/#datar.base.verbs.append
 [148]: ../../api/datar.base.verbs/#datar.base.verbs.proportions
+[149]: ../../api/datar.base.string/#datar.base.string.trimws
+[150]: ../../api/datar.base.date/#datar.base.date.as_pd_date
diff --git a/docs/style.css b/docs/style.css
index cece3bfb..099b7766 100644
--- a/docs/style.css
+++ b/docs/style.css
@@ -1,4 +1,7 @@
 
+.md-main__inner.md-grid {
+    max-width: 80%;
+}
 
 .md-typeset .admonition, .md-typeset details {
     font-size: .7rem !important;
diff --git a/mkdocs.yml b/mkdocs.yml
index f03cd40a..c07df8e7 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -58,6 +58,7 @@ nav:
         'Grouped/rowwise data frame': 'caveats/grouped.md'
         'NAs': 'caveats/NAs.md'
         'in vs %in%': 'caveats/in.md'
+        '"blind" enviroment': 'caveats/blind.md'
     - 'Datasets': 'datasets.md'
     - 'Advanced usage': 'advanced.md'
     - 'Examples':
@@ -85,6 +86,11 @@ nav:
         'fill': 'notebooks/fill.ipynb'
         'filter': 'notebooks/filter.ipynb'
         'filter-joins': 'notebooks/filter-joins.ipynb'
+        'forcats_fct_multi': 'notebooks/forcats_fct_multi.ipynb'
+        'forcats_lvl_addrm': 'notebooks/forcats_lvl_addrm.ipynb'
+        'forcats_lvl_order': 'notebooks/forcats_lvl_order.ipynb'
+        'forcats_lvl_value': 'notebooks/forcats_lvl_value.ipynb'
+        'forcats_misc': 'notebooks/forcats_misc.ipynb'
         'full_seq': 'notebooks/full_seq.ipynb'
         'datar': 'notebooks/datar.ipynb'
         'group_by': 'notebooks/group_by.ipynb'
diff --git a/pyproject.toml b/pyproject.toml
index f57e3c56..1ce94431 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "datar"
-version = "0.5.0"
+version = "0.5.1"
 description = "Port of dplyr and other related R packages in python, using pipda."
 authors = ["pwwang <pwwang@pwwang.com>"]
 readme = "README.md"
diff --git a/tests/test_base_date.py b/tests/test_base_date.py
index 9a7c6081..4754fa35 100644
--- a/tests/test_base_date.py
+++ b/tests/test_base_date.py
@@ -1,5 +1,6 @@
 import pytest
 
+import pandas
 from datar.base.date import *
 from .conftest import assert_iterable_equal
 
@@ -47,7 +48,7 @@ def test_as_date(x, format, try_formats, optional, tz, origin, expected):
         optional,
         tz,
         origin
-    ), expected)
+    ), pandas.to_datetime(expected))
 
 def test_as_date_error():
     with pytest.raises(ValueError):
@@ -57,3 +58,7 @@ def test_as_date_error():
         as_date("1990-1-1", "%Y")
 
     assert as_date("1990-1-1", "Y", optional=True).isna().all()
+
+def test_as_pd_date():
+
+    assert as_pd_date("Sep 16, 2021") == pandas.Timestamp('2021-09-16 00:00:00')