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The stand-alone command-line compiler

Author(s): Daniel Cabeza and the CLIP Group.

Version: 1.10#6 (2004/8/7, 21:46:39 CEST)

Version of last change: 1.9#98 (2003/8/27, 12:39:15 CEST)

ciaoc [CH00b] is the Ciao stand-alone command-line compiler. ciaoc can be used to create executables or to compile individual files to object code (to be later linked with other files). ciaoc is specially useful when working from the command line. Also, it can be called to compile Ciao programs from other tools such as, e.g., shell scripts, Makefiles, or project files. All the capabilities of ciaoc are also available from the interactive top-level shell, which uses the ciaoc modules as its components.

Introduction to building executables

An executable can be built from a single file or from a collection of inter-related files. In the case of only one file, this file must define the predicate main/0 or main/1. This predicate is the one which will be called when the executable is started. As an example, consider the following file, called hello.pl:

main :-
     write('Hello world'), 

To compile it from the command line using the ciaoc standalone compiler it suffices to type "ciaoc hello" (in Win32 you may have to put the complete path to the ciaoc folder of the Ciao distribution, where the installation process leaves a ciaoc.bat file):

[60]> ciaoc hello


This produces an executable called hello in Un*x-like systems and hello.cpx under Win32 systems. This executable can then be run in Win32 by double-clicking on it and on Un*x systems by simply typing its name (see for section Running executables from the command line for how to run executables from the command line in Win32):

[61]> hello
Hello world

If the application is composed of several files the process is identical. Assume hello.pl is now:

:- use_module(aux,[p/1]).

main :-

where the file aux.pl contains:

:- module(aux,[p/1]).

p('Hello world').

This can again be compiled using the ciaoc standalone compiler as before:

[60]> ciaoc hello

[61]> hello
Hello world

The invocation of ciaoc hello compiles the file hello.pl and all connected files that may need recompilation -- in this case the file aux.pl. Also, if any library files used had not been compiled previously they would be compiled at this point (See section Intermediate files in the compilation process). Also, if, say, hello.pl is changed and recompiled, the object code resulting from the previous compilation of aux.pl will be reused. This is all done without any need for Makefiles, and considerably accelerates the development process for large applications. This process can be observed by selecting the -v option when invoking ciaoc (which is equivalent to setting the verbose_compilation Prolog flag to on in the top-level interpreter).

If main/1 is defined instead of main/0 then when the executable is started the argument of main/1 will be instantiated to a list of atoms, each one of them corresponding to a command line option. Consider the file say.pl:

main(Argv) :-
     write_list(Argv), nl.

write_list([Arg|Args]) :- 
     write(' '),

Compiling this program and running it results in the following output:

[91]> ciaoc say

[91]> say hello dolly
hello dolly 

The name of the generated executable can be controlled with the -o option (See section Usage (ciaoc)).

Paths used by the compiler during compilation

The compiler will look for files mentioned in commands such as use_module/1 or ensure_loaded/1 in the current directory. Other paths can be added by including them in a file whose name is given to ciaoc using the -u option. This file should contain facts of the predicates file_search_path/2 and library_directory/1 (see the documentation for these predicates and also section Customizing library paths and path aliases for details).

Running executables from the command line

As mentioned before, what the ciaoc compiler generates and how it is started varies somewhat from OS to OS. In general, the product of compiling an application with ciaoc is a file that contains the bytecode (the product of the compilation) and invokes the Ciao engine on it.

Except for a couple of header lines, the contents of executables are almost identical under different OSs (except for self-contained ones). The bytecode they contain is architecture-independent. In fact, it is possible to create an executable under Un*x and run it on Windows or viceversa, by making only minor modifications (e.g., creating the .bat file and/or setting environment variables or editing the start of the file to point to the correct engine location).

Types of executables generated

While the default options used by ciaoc are sufficient for normal use, by selecting other options ciaoc can generate several different types of executables, which offer interesting tradeoffs among size of the generated executable, portability, and startup time [CH00b]:

Dynamic executables:
ciaoc produces by default dynamic executables. In this case the executable produced is a platform-independent file which includes in compiled form all the user defined files. On the other hand, any system libraries used by the application are loaded dynamically at startup. More precisely, any files that appear as library(...) in use_module/1 and ensure_loaded/1 declarations will not be included explicitly in the executable and will instead be loaded dynamically. Is is also possible to mark other path aliases (see the documentation for file_search_path/2) for dynamic loading by using the -d option. Files accessed through such aliases will also be loaded dynamically. Dynamic loading allows making smaller executables. Such executables may be used directly in the same machine in which they were compiled, since suitable paths to the location of the libraries will be included as default in the executable by ciaoc during compilation. The executable can also be used in another machine, even if the architecture and OS are different. The requirement is that the Ciao libraries (which will also include the appropriate Ciao engine for that architecture and OS) be installed in the target machine, and that the CIAOLIB and CIAOENGINE environment variables are set appropriately for the executable to be able to find them (see section Environment variables used by Ciao executables). How to do this differs slightly from OS to OS.
Static executables:
Selecting the -s option ciaoc produces a static executable. In this case the executable produced (again a platform-independent file) will include in it all the auxiliary files and any system libraries needed by the application. Thus, such an executable is almost complete, needing in order to run only the Ciao engine, which is platform-specific.(1) Again, if the executable is run in the same machine in which it was compiled then the engine is found automatically. If the executable is moved to another machine, the executable only needs access to a suitable engine (which can be done by setting the CIAOENGINE environment variable to point to this engine). This type of compilation produces larger executables, but has the advantage that these executables can be installed and run in a different machine, with different architecture and OS, even if Ciao is not installed on that machine. To install (or distribute) such an executable, one only needs to copy the executable file itself and the appropriate engine for the target platform (See section Installing Ciao from the source distribution or section Installing Ciao from a Win32 binary distribution and section Multiarchitecture support), and to set things so that the executable can find the engine. (2)
Dynamic executables, with lazy loading:
Selecting the -l option is very similar to the case of dynamic executables above, except that the code in the library modules is not loaded when the program is started but rather it is done during execution, the first time a predicate defined in that file is called. This is advantageous if a large application is composed of many parts but is such that typically only some of the parts are used in each invocation. The Ciao preprocessor, ciaopp, is a good example of this: it has many capabilitites but typically only some of them are used in a given session. An executable with lazy load has the advantage that it starts fast, loading a minimal functionality on startup, and then loads the different modules automatically as needed. Please beware that initialization directives appearing in a module which is lazily loaded currently are not executed until the module is effectively loaded. Since this happens when the module is first required at runtime, the compiler cannot guarantee the exact time and order in which these directives are executed.
Self-contained executables:
Self-contained executables are static executables (i.e., this option also implies static compilation) which include a Ciao engine along with the bytecode, so they do not depend on an external one for their execution. This is useful to create executables which run even if the machine where the program is to be executed does not have a Ciao engine installed and/or libraries. The disadvantage is that such execuatbles are platform-dependent (as well as larger than those that simply use an external library). This type of compilation is selected with the -S option. Cross-compilation is also possible with the -SS option, so you can specify the target OS and architecture (e.g. LINUXi86). To be able to use the latter option, it is necessary to have installed a ciaoengine for the target machine in the Ciao library (this requires compiling the engine in that OS/architecture and installing it, so that it is available in the library).
Compressed executables:
In compressed executables the bytecode is compressed. This allows producing smaller executables, at the cost of a slightly slower startup time. This is selected with the -z option. You can also produce compressed libraries if you use -zl along with the -c option. If you select -zl while generating an executable, any library which is compiled to accomplish this will be also compressed.
Active modules:
The compiler can also compile (via the -a option) a given file into an active module (see section Active modules (high-level distributed execution) for a description of this).

Environment variables used by Ciao executables

The executables generated by the Ciao compiler (including the ciao development tools themselves) locate automatically where the Ciao engine and libraries have been installed, since those paths are stored as defaults in the engine and compiler at installation time. Thus, there is no need for setting any environment variables in order to run Ciao executables (on a single architecture -- see section Multiarchitecture support for running on multiple architectures).

However, the default paths can be overridden by using the environment variables CIAOENGINE and CIAOLIB. The first one will tell the Ciao executables where to look for an engine, and the second will tell them where to look for the libraries. Thus, it is possible to actually use the Ciao system without installing it by setting these variables to the following values:

where $(CIAOARCH) is the string echoed by the command SRC/etc/ciao_get_arch (or BINROOT/ciao_get_arch, after installation).

This allows using alternate engines or libraries, which can be very useful for system development and experimentation.

Intermediate files in the compilation process

Compiling an individual source (i.e., .pl) file produces a .itf file and a .po file. The .itf file contains information of the modular interface of the file, such as information on exported and imported predicates and on the other modules used by this module. This information is used to know if a given file should be recompiled at a given point in time and also to be able to detect more errors statically including undefined predicates, mismatches on predicate charaterictics across modules, etc. The .po file contains the platform-independent object code for a file, ready for linking (statically or dynamically).

It is also possible to use ciaoc to explicitly generate the .po file for one or more .pl files by using the -c option.

Usage (ciaoc)

The following provides details on the different command line options available when invoking ciaoc:

ciaoc <MiscOpts> <ExecOpts> [-o <execname>] <file> ...

  Make an executable from the listed files.  If there is
  more than one file, they must be non-module, and the
  first one must include the main predicate.  The -o
  option allows generating an arbitrary executable name.

ciaoc <MiscOpts> <ExecOpts> -a <publishmod> <module>

  Make an active module executable from <module> with
  address publish module <publishmod>.

ciaoc <MiscOpts> -c  <file> ...

  Compile listed files (make .po objects).

<MiscOpts> can be: [-v] [-ri] [-u <file>]

-v  verbose mode

-ri generate human readable .itf files

-u  use <file> for compilation

<ExecOpts> can be: [-s|-S|-SS <target>|-z|-zl|-e|-l|(-ll <module>)*]
                   (-d <alias>)* [-x]

-s  make a static executable (otherwise dynamic files are not included)

-S  make standalone executable for the current OS and architecture

-SS make standalone executable for <target> OS and architecture
    valid <target> values may be: LINUXi86, SolarisSparc...

    (both -S and -SS imply -s)

-z  generate executables with compressed bytecode

-zl generate libraries with compressed bytecode - any library (re)compiled
    as consequence of normal executable compilation will also be affected

-e  make executable with eager load of dynamic files at startup (default)

-l  idem with lazy load of dynamic files (except insecure cases)

-ll force <module> to be loaded lazily,  implies -l

-d  files using this path alias are dynamic (default: library)

-x  Extended recompilation: only useful for Ciao standard library developers

default extension for files is '.pl'

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