Simple Scripts
==============

Simplest script in haskell looks like this:
[simple.hs](./simple.hs):

.. include:: simple.hs
   :code: haskell

Just mark this file as executable (via ``chmod +x
./simple_stdin_stdout.hs``) and launch as usual::

    $ ./simple_stdin_stdout.hs
    hello, scripting!

You can **compile your script** to get an executable like this::

    $ stack ghc --resolver=lts-12.7 ./simple_stdin_stdout.hs
    Linking simple_stdin_stdout ...
    $ ./simple_stdin_stdout
    hello, scripting!

With a ``stack script`` shown above, you can use whatever packages are
present in `a snapshot <https://www.stackage.org/lts-12.7>`_ without
listing them out. For example:
`simple_with_dep.hs <simple_with_dep.hs>`_:

.. include:: simple_with_dep.hs
   :code: haskell

If you want to use a non-snapshot dependency, you can use a ``stack runghc`` (or ``stack ghc``) command with dependency packages being listed in a ``--package`` argument: `simple_stdin_stdout_nonsnapshot_dep.hs <simple_stdin_stdout_nonsnapshot_dep.hs>`_:

.. include:: simple_stdin_stdout_nonsnapshot_dep.hs
   :code: haskell

Notes/Caveats:

- TODO compiling with Wall/Werror and other flags
- buffering (per-line? per-byte? need to set buffering mode)
- best practice: upon reading/writing to stdin/stdout, usage of
  `String` is bad, better use `Text`, best -- bytestrings (TODO: citation on
  encoding problems needed)