===================================
   Nimrod Compiler User Guide
===================================

:Author: Andreas Rumpf
:Version: |nimrodversion|

.. contents::

  "Look at you, hacker. A pathetic creature of meat and bone, panting and
  sweating as you run through my corridors. How can you challenge a perfect,
  immortal machine?"


Introduction
============

This document describes the usage of the *Nimrod compiler*
on the different supported platforms. It is not a definition of the Nimrod
programming language (therefore is the `manual <manual.html>`_).

Nimrod is free software; it is licensed under the
`GNU General Public License <gpl.html>`_.


Compiler Usage
==============

Command line switches
---------------------
Basic command line switches are:

.. include:: basicopt.txt

Advanced command line switches are:

.. include:: advopt.txt


Configuration files
-------------------

**Note:** The *project file name* is the name of the ``.nim`` file that is 
passed as a command line argument to the compiler.


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

1) ``$nimrod/config/nimrod.cfg``, ``/etc/nimrod.cfg`` (UNIX) or ``%NIMROD%/config/nimrod.cfg`` (Windows). This file can be skipped with the ``--skipCfg`` command line option.
2) ``/home/$user/.config/nimrod.cfg`` (UNIX) or  ``%APPDATA%/nimrod.cfg`` (Windows). This file can be skipped with the ``--skipUserCfg`` command line option.
3) ``$parentDir/nimrod.cfg`` where ``$parentDir`` stands for any parent  directory of the project file's path. These files can be skipped with the ``--skipParentCfg`` command line option.
4) ``$projectDir/nimrod.cfg`` where ``$projectDir`` stands for the project  file's path. This file can be skipped with the ``--skipProjCfg`` command line option.
5) A project can also have a project specific configuration file named ``$project.nimrod.cfg`` that resides in the same directory as ``$project.nim``. This file can be skipped with the ``--skipProjCfg`` command line option.


Command line settings have priority over configuration file settings.

The default build of a project is a `debug build`:idx:. To compile a 
`release build`:idx: define the ``release`` symbol::
  
  nimrod c -d:release myproject.nim


Generated C code directory
--------------------------
The generated files that Nimrod produces all go into a subdirectory called
``nimcache`` in your project directory. This makes it easy to delete all
generated files.

However, the generated C code is not platform independent. C code generated for
Linux does not compile on Windows, for instance. The comment on top of the
C file lists the OS, CPU and CC the file has been compiled for.


Compilation cache
=================

**Warning**: The compilation cache is still highly experimental!

The ``nimcache`` directory may also contain so called `rod`:idx: 
or `symbol files`:idx:. These files are pre-compiled modules that are used by
the compiler to perform `incremental compilation`:idx:. This means that only
modules that have changed since the last compilation (or the modules depending
on them etc.) are re-compiled. However, per default no symbol files are 
generated; use the ``--symbolFiles:on`` command line switch to activate them.

Unfortunately due to technical reasons the ``--symbolFiles:on`` needs 
to *aggregate* some generated C code. This means that the resulting executable
might contain some cruft even when dead code elimination is turned on. So
the final release build should be done with ``--symbolFiles:off``.

Due to the aggregation of C code it is also recommended that each project
resists in its own directory so that the generated ``nimcache`` directory
is not shared between different projects.


Cross compilation
=================

To `cross compile`:idx:, use for example::

  nimrod c --cpu:i386 --os:linux --compile_only --gen_script myproject.nim

Then move the C code and the compile script ``compile_myproject.sh`` to your 
Linux i386 machine and run the script.

Another way is to make Nimrod invoke a cross compiler toolchain::
  
  nimrod c --cpu:arm --os:linux myproject.nim
  
For cross compilation, the compiler invokes a C compiler named 
like ``$cpu.$os.$cc`` (for example arm.linux.gcc) and the configuration 
system is used to provide meaningful defaults. For example for ``ARM`` your
configuration file should contain something like::

  arm.linux.gcc.path = "/usr/bin"
  arm.linux.gcc.exe = "arm-linux-gcc"
  arm.linux.gcc.linkerexe = "arm-linux-gcc"


DLL generation
==============

Nimrod supports the generation of DLLs. However, there must be only one 
instance of the GC per process/address space. This instance is contained in
``nimrtl.dll``. This means that every generated Nimrod `DLL`:idx: depends
on ``nimrtl.dll``. To generate the "nimrtl.dll" file, use the command::
  
  nimrod c -d:release lib/nimrtl.nim

To link against ``nimrtl.dll`` use the command::

  nimrod c -d:useNimRtl myprog.nim

**Note**: Currently the creation of ``nimrtl.dll`` with thread support has 
never been tested and is unlikely to work!


Additional compilation switches
===============================

The standard library supports a growing number of ``useX`` conditional defines
affecting how some features are implemented. This section tries to give a
complete list.

==================   =========================================================
Define               Effect
==================   =========================================================
``release``          Turns off runtime checks and turns on the optimizer.
``useWinAnsi``       Modules like ``os`` and ``osproc`` use the Ansi versions
                     of the Windows API. The default build uses the Unicode
                     version.s
``useFork``          Makes ``osproc`` use ``fork`` instead of ``posix_spawn``.
``useNimRtl``        Compile and link against ``nimrtl.dll``.
``useMalloc``        Makes Nimrod use C's `malloc`:idx: instead of Nimrod's 
                     own memory manager. This only works with ``gc:none``.
``useRealtimeGC``    Enables support of Nimrod's GC for *soft* realtime 
                     systems. See the documentation of the `gc <gc.html>`_ 
                     for further information.
``nodejs``           The EcmaScript target is actually ``node.js``.
==================   =========================================================



Additional Features
===================

This section describes Nimrod's additional features that are not listed in the
Nimrod manual. Some of the features here only make sense for the C code
generator and are subject to change.


NoDecl pragma
-------------
The `noDecl`:idx: pragma can be applied to almost any symbol (variable, proc,
type, etc.) and is sometimes useful for interoperability with C:
It tells Nimrod that it should not generate a declaration for the symbol in
the C code. For example:

.. code-block:: Nimrod
  var
    EACCES {.importc, noDecl.}: cint # pretend EACCES was a variable, as
                                     # Nimrod does not know its value

However, the ``header`` pragma is often the better alternative.

**Note**: This will not work for the LLVM backend.


Header pragma
-------------
The `header`:idx: pragma is very similar to the ``noDecl`` pragma: It can be
applied to almost any symbol and specifies that it should not be declared
and instead the generated code should contain an ``#include``:

.. code-block:: Nimrod
  type
    PFile {.importc: "FILE*", header: "<stdio.h>".} = distinct pointer
      # import C's FILE* type; Nimrod will treat it as a new pointer type

The ``header`` pragma always expects a string constant. The string contant
contains the header file: As usual for C, a system header file is enclosed
in angle brackets: ``<>``. If no angle brackets are given, Nimrod
encloses the header file in ``""`` in the generated C code.

**Note**: This will not work for the LLVM backend.


IncompleteStruct pragma
-----------------------
The `incompleteStruct`:idx: pragma tells the compiler to not use the 
underlying C ``struct`` in a ``sizeof`` expression:

.. code-block:: Nimrod
  type
    TDIR* {.importc: "DIR", header: "<dirent.h>", 
            final, pure, incompleteStruct.} = object


Compile pragma
--------------
The `compile`:idx: pragma can be used to compile and link a C/C++ source file 
with the project: 

.. code-block:: Nimrod
  {.compile: "myfile.cpp".}

**Note**: Nimrod computes a CRC checksum and only recompiles the file if it 
has changed. You can use the ``-f`` command line option to force recompilation
of the file.


Link pragma
-----------
The `link`:idx: pragma can be used to link an additional file with the project: 

.. code-block:: Nimrod
  {.link: "myfile.o".}


Emit pragma
-----------
The `emit`:idx: pragma can be used to directly affect the output of the 
compiler's code generator. So it makes your code unportable to other code
generators/backends. Its usage is highly discouraged! However, it can be
extremely useful for interfacing with `C++`:idx: or `Objective C`:idx: code.

Example:

.. code-block:: Nimrod
  {.emit: """
  static int cvariable = 420;
  """.}

  proc embedsC() {.noStackFrame.} = 
    var nimrodVar = 89
    # use backticks to access Nimrod symbols within an emit section:
    {.emit: """fprintf(stdout, "%d\n", cvariable + (int)`nimrodVar`);""".}

  embedsC()


ImportCpp pragma
----------------
The `importcpp`:idx: pragma can be used to import `C++`:idx: methods. The
generated code then uses the C++ method calling syntax: ``obj->method(arg)``.
In addition with the ``header`` and ``emit`` pragmas this allows *sloppy*
interfacing with libraries written in C++:

.. code-block:: Nimrod
  # Horrible example of how to interface with a C++ engine ... ;-)

  {.link: "/usr/lib/libIrrlicht.so".}

  {.emit: """
  using namespace irr;
  using namespace core;
  using namespace scene;
  using namespace video;
  using namespace io;
  using namespace gui;
  """.}

  const
    irr = "<irrlicht/irrlicht.h>"

  type
    TIrrlichtDevice {.final, header: irr, importc: "IrrlichtDevice".} = object
    PIrrlichtDevice = ptr TIrrlichtDevice

  proc createDevice(): PIrrlichtDevice {.
    header: irr, importc: "createDevice".}
  proc run(device: PIrrlichtDevice): bool {.
    header: irr, importcpp: "run".}
  
The compiler needs to be told to generate C++ (command ``cpp``) for 
this to work. The conditional symbol ``cpp`` is defined when the compiler
emits C++ code.


ImportObjC pragma
-----------------
The `importobjc`:idx: pragma can be used to import `Objective C`:idx: methods. 
The generated code then uses the Objective C method calling 
syntax: ``[obj method param1: arg]``.
In addition with the ``header`` and ``emit`` pragmas this allows *sloppy*
interfacing with libraries written in Objective C:

.. code-block:: Nimrod
  # horrible example of how to interface with GNUStep ...

  {.passL: "-lobjc".}
  {.emit: """
  #include <objc/Object.h>
  @interface Greeter:Object
  {
  }

  - (void)greet:(long)x y:(long)dummy;
  @end

  #include <stdio.h>
  @implementation Greeter

  - (void)greet:(long)x y:(long)dummy
  {
	  printf("Hello, World!\n");
  }
  @end

  #include <stdlib.h>
  """.}

  type
    TId {.importc: "id", header: "<objc/Object.h>", final.} = distinct int

  proc newGreeter: TId {.importobjc: "Greeter new", nodecl.}
  proc greet(self: TId, x, y: int) {.importobjc: "greet", nodecl.}
  proc free(self: TId) {.importobjc: "free", nodecl.}

  var g = newGreeter()
  g.greet(12, 34)
  g.free()

The compiler needs to be told to generate Objective C (command ``objc``) for 
this to work. The conditional symbol ``objc`` is defined when the compiler
emits Objective C code.


LineDir option
--------------
The `lineDir`:idx: option can be turned on or off. If turned on the
generated C code contains ``#line`` directives. This may be helpful for
debugging with GDB.


StackTrace option
-----------------
If the `stackTrace`:idx: option is turned on, the generated C contains code to
ensure that proper stack traces are given if the program crashes or an
uncaught exception is raised.


LineTrace option
----------------
The `lineTrace`:idx: option implies the ``stackTrace`` option. If turned on,
the generated C contains code to ensure that proper stack traces with line
number information are given if the program crashes or an uncaught exception
is raised.

Debugger option
---------------
The `debugger`:idx: option enables or disables the *Embedded Nimrod Debugger*.
See the documentation of endb_ for further information.


Breakpoint pragma
-----------------
The *breakpoint* pragma was specially added for the sake of debugging with
ENDB. See the documentation of `endb <endb.html>`_ for further information.


Volatile pragma
---------------
The `volatile`:idx: pragma is for variables only. It declares the variable as
``volatile``, whatever that means in C/C++ (its semantics are not well defined
in C/C++).

**Note**: This pragma will not exist for the LLVM backend.


Nimrod interactive mode
=======================

The Nimrod compiler supports an `interactive mode`:idx:. This is also known as
a `REPL`:idx: (*read eval print loop*). If Nimrod has been built with the 
``-d:useGnuReadline`` switch, it uses the GNU readline library for terminal
input management. To start Nimrod in interactive mode use the command 
``nimrod i``. To quit use the ``quit()`` command. To determine whether an input
line is an incomplete statement to be continued these rules are used:

1. The line ends with ``[-+*/\\<>!\?\|%&$@~,;:=#^]\s*$`` (operator symbol followed by optional whitespace).
2. The line starts with a space (indentation).
3. The line is within a triple quoted string literal. However, the detection 
   does not work if the line contains more than one ``"""``.


Nimrod for embedded systems
===========================

The standard library can be avoided to a point where C code generation 
for a 16bit micro controllers is feasible. Use the `standalone`:idx: target
(``--os:standalone``) for a bare bones standard library that lacks any
OS features.

To make the compiler output code for a 16bit target use the ``--cpu:avr`` 
target.

So to generate code for an `AVR`:idx: processor use this command::
  
  nimrod c --cpu:avr --os:standalone --gc:none -d:useMalloc --genScript x.nim


Nimrod for realtime systems
===========================

See the documentation of Nimrod's soft realtime `GC <gc.html>`_ for further 
information.


Debugging with Nimrod
=====================

Nimrod comes with its own *Embedded Nimrod Debugger*. See
the documentation of endb_ for further information.


Optimizing for Nimrod
=====================

Nimrod has no separate optimizer, but the C code that is produced is very
efficient. Most C compilers have excellent optimizers, so usually it is
not needed to optimize one's code. Nimrod has been designed to encourage
efficient code: The most readable code in Nimrod is often the most efficient
too.

However, sometimes one has to optimize. Do it in the following order:

1. switch off the embedded debugger (it is **slow**!)
2. turn on the optimizer and turn off runtime checks
3. profile your code to find where the bottlenecks are
4. try to find a better algorithm
5. do low-level optimizations

This section can only help you with the last item.


Optimizing string handling
--------------------------

String assignments are sometimes expensive in Nimrod: They are required to
copy the whole string. However, the compiler is often smart enough to not copy
strings. Due to the argument passing semantics, strings are never copied when
passed to subroutines. The compiler does not copy strings that are a result from
a procedure call, because the callee returns a new string anyway.
Thus it is efficient to do:

.. code-block:: Nimrod
  var s = procA() # assignment will not copy the string; procA allocates a new
                  # string already

However it is not efficient to do:

.. code-block:: Nimrod
  var s = varA    # assignment has to copy the whole string into a new buffer!

For ``let`` symbols a copy is not always necessary:

.. code-block:: Nimrod
  let s = varA    # may only copy a pointer if it safe to do so


If you know what you're doing, you can also mark single string (or sequence)
objects as `shallow`:idx:\:

.. code-block:: Nimrod
  var s = "abc"
  shallow(s) # mark 's' as shallow string
  var x = s  # now might does not copy the string!
  
Usage of ``shallow`` is always safe once you know the string won't be modified
anymore, similar to Ruby's `freeze`:idx:.


The compiler optimizes string case statements: A hashing scheme is used for them
if several different string constants are used. So code like this is reasonably
efficient:

.. code-block:: Nimrod
  case normalize(k.key)
  of "name": c.name = v
  of "displayname": c.displayName = v
  of "version": c.version = v
  of "os": c.oses = split(v, {';'})
  of "cpu": c.cpus = split(v, {';'})
  of "authors": c.authors = split(v, {';'})
  of "description": c.description = v
  of "app":
    case normalize(v)
    of "console": c.app = appConsole
    of "gui": c.app = appGUI
    else: quit(errorStr(p, "expected: console or gui"))
  of "license": c.license = UnixToNativePath(k.value)
  else: quit(errorStr(p, "unknown variable: " & k.key))