λ encoding
==========

.. admonition:: Summary

    Using a custom codec instead of an import hook.


    `Source code <https://github.com/aroberge/ideas/blob/master/ideas/examples/lambda_codec.py>`_


.. warning::

    The following is just a quick first draft. The code shown here
    might be completely out of date and not work as written.
    As of version 0.0.17, the console example shown below did work.

Suppose we want to run a program that has a custom encoding;
in this case, we use ``λ`` to represent Python's ``lambda`` keyword::

    # coding: lambda-encoding

    square = λ x: x**2

    assert square(3) == 9

    print("Using lambda-encoding: λ")  # λ is not converted inside strings

    if __name__ == '__main__':
        print("The square of 5 is", square(5))

Before we can do this, we need to make Python aware of the existence
of our custom encoding. This can be done by having the following
program::

    # usercustomize.py

    from ideas.examples import lambda_codec  # noqa

    print("  --> usercustomize.py was executed")


By setting ``PYTHONPATH`` to a directory where a program named
``usercustomize.py`` is found, any such program is automatically run before
the main script.

As we can see, when we run it, the source transformation is done
correctly.

.. code-block:: none

    TESTS:\lambda_encoding
    $ set PYTHONPATH=%CD%

    TESTS:\lambda_encoding
    $ python short_program.py
      --> usercustomize.py was executed
    Using lambda-encoding: λ
    The square of 5 is 25


We can also use the **ideas** console and have our special encoding be used.::

    >>> from ideas.examples import lambda_codec
    >>> from ideas import console
    >>> console.start()
    Configuration values for the console:
        transform_source from ideas.examples.lambda_codec
    --------------------------------------------------
    Ideas Console version 0.0.17. [Python version: 3.7.3]

    ~>> sq = λ x: x*x
    ~>> sq(3)
    9

.. automodule:: ideas.examples.lambda_codec
   :members:

.. automodule:: ideas.custom_encoding
   :members: