Nim/doc/nims.rst

================================
          NimScript
================================

Strictly speaking, ``NimScript`` is the subset of Nim that can be evaluated
by Nim's builtin virtual machine (VM). This VM is used for Nim's compiletime
function evaluation features.

The ``nim`` executable processes the ``.nims`` configuration files in
the following directories (in this order; later files overwrite
previous settings):

1) If environment variable ``XDG_CONFIG_HOME`` is defined,
   ``$XDG_CONFIG_HOME/nim/config.nims`` or
   ``~/.config/nim/config.nims`` (POSIX) or
   ``%APPDATA%/nim/config.nims`` (Windows). This file can be skipped
   with the ``--skipUserCfg`` command line option.
2) ``$parentDir/config.nims`` where ``$parentDir`` stands for any
   parent directory of the project file's path. These files can be
   skipped with the ``--skipParentCfg`` command line option.
3) ``$projectDir/config.nims`` where ``$projectDir`` stands for the
   project's path. This file can be skipped with the ``--skipProjCfg``
   command line option.
4) A project can also have a project specific configuration file named
   ``$project.nims`` that resides in the same directory as
   ``$project.nim``. This file can be skipped with the same
   ``--skipProjCfg`` command line option.

The VM cannot deal with ``importc`` because the FFI is not
available. So the stdlib modules using ``importc`` cannot be used with
Nim's VM. However, at least the following modules are available:

* `macros <macros.html>`_
* `os <os.html>`_
* `strutils <strutils.html>`_
* `math <math.html>`_
* `distros <distros.html>`_

In addition to the standard Nim syntax (`system <system.html>`_
module), NimScripts support the procs and templates defined in the
`nimscript <nimscript.html>`_ module too.


NimScript as a configuration file
=================================

A command-line switch ``--FOO`` is written as ``switch("FOO")`` in
NimScript. Similarly, command-line ``--FOO:VAL`` translates to
``switch("FOO", "VAL")``.

Here are few examples of using the ``switch`` proc:

.. code-block:: nim
  # command-line: --opt:size
  switch("opt", "size")
  # command-line: --define:foo or -d:foo
  switch("define", "foo")
  # command-line: --forceBuild
  switch("forceBuild")

NimScripts also support ``--`` templates for convenience, which look
like command-line switches written as-is in the NimScript file. So the
above example can be rewritten as:

.. code-block:: nim
  --opt:size
  --define:foo
  --forceBuild

**Note**: In general, the *define* switches can also be set in
NimScripts using ``switch`` or ``--``, as shown in above
examples. Only the ``release`` define (``-d:release``) cannot be set
in NimScripts.


NimScript as a build tool
=========================

The ``task`` template that the ``system`` module defines allows a NimScript
file to be used as a build tool. The following example defines a
task ``build`` that is an alias for the ``c`` command:

.. code-block:: nim
  task build, "builds an example":
    setCommand "c"


In fact, as a convention the following tasks should be available:

=========     ===================================================
Task          Description
=========     ===================================================
``help``      List all the available NimScript tasks along with their docstrings.
``build``     Build the project with the required
              backend (``c``, ``cpp`` or ``js``).
``tests``     Runs the tests belonging to the project.
``bench``     Runs benchmarks belonging to the project.
=========     ===================================================


If the task runs an external command via ``exec`` it should afterwards call
``setCommand "nop"`` to tell the Nim compiler that nothing else needs to be
done:

.. code-block:: nim

  task tests, "test regular expressions":
    exec "nim c -r tests"
    setCommand "nop"


Look at the module `distros <distros.html>`_ for some support of the
OS's native package managers.


Nimble integration
==================

See the `Nimble readme <https://github.com/nim-lang/nimble#readme>`_
for more information.




Standalone NimScript
====================

NimScript can also be used directly as a portable replacement for Bash and
Batch files. Use ``nim e myscript.nims`` to run ``myscript.nims``. For example,
installation of Nimble could be accomplished with this simple script:

.. code-block:: nim

  mode = ScriptMode.Verbose

  var id = 0
  while dirExists("nimble" & $id):
    inc id

  exec "git clone https://github.com/nim-lang/nimble.git nimble" & $id

  withDir "nimble" & $id & "/src":
    exec "nim c nimble"

  mvFile "nimble" & $id & "/src/nimble".toExe, "bin/nimble".toExe

You can also use the shebang ``#!/usr/bin/env nim``, as long as your filename
ends with ``.nims``:

.. code-block:: nim

  #!/usr/bin/env nim
  mode = ScriptMode.Silent

  echo "hello world"