Appendix F GNAT Ada

The Gnat (GNU Ada Translator) project has developed a fully fledged Ada compiler that will 
work with the GNU linker. This will allow the compiler to be ported to any target 
that the GNU compiler/linker system is currently available for. The compiler  is 
implementing the 1995 revision to the language, and so provides support for object 
oriented programming, enhanced concurrency support as well as numerous other 
features such as child and private child packages.


The Gnat Ada compiler does away with the traditional library implementation of 
most Ada systems and presents a more traditional environment. Source code is 
compiled into a .o and a .ali file. The .o  represents the translation of the 
instructions, the .ali file contains information about the relationship of the source to 
other components in the system.

Gnat Ada source code must be in a file that has the same name as the compilation 
unit name, with either a .ads (for specifications) or a .adb (for bodies).

Packages with child units (such as unix.file) should have the dot replaced with a '-', 
and the usual .ads or .adb suffix appended.

For example the following program must be placed into a file called demo.adb.

with simple_io;	use simple_io;
procedure demo is
begin
	for i in 1..10 loop
		put("hello world");
		new_line;
	end loop;
end;

To compile this you type in the following...

	gcc -c fred.adb

Typical questions now asked at this stage...

Do you mean that the C compiler actually compiles this program?
Does this mean that the code is compiled to C?

The answer to both of these questions is NO!

gcc is not a compiler, it is a program that inspects the file suffix (e.g. .c, .adb, .ads, 
.c++) and then invokes the appropriate compiler. The gnat (GNu Ada Translator) 
compiles the program into the standard GNU intermediate code representation, 
which is then taken by the code generator specific for the computer you are 
running, and produces a normal '.o' object file.
Now that that's out of the way...

To link you program...

gnatbl  demo.ali

It doesn't matter how many other procedures/packages you with, you don't need to 
specify them in the link option.
However if you want to link in some C routines, then you may have to do the 
following (this example is taken from an example using the C curses library)....

gnatbl demo.ali -lcurses


Sharing software

The Gnat compiler looks for the environment variables ADA_INCLUDE_PATH 
and ADA_OBJECT_PATH. Any directory in these path variables will be searched 
for source code and object code, respectively.
In this way a group can share some commonly developed routines.


Compiler source code (and source to all Ada standard packages)

Currently on Arcadia/Yallara the source for the compiler and all the Ada standard 
packages are in the directory

/opt/gnu/adainclude

Some of these names have been 'crunched' (i.e. reduces to 8.3 DOS filename 
conventions) so it is not always immediately obvious where a package spec. 
resides. For example the text_io package can be found in the file

a-textio.ads (ada.text_io package specification)

Other packages of interest are...

interfac.ads		package Interface
i-c.ads		package Interface.C
i-cpoint.ads		package Interface.C.Pointers
i-cstrin.ads		pacakge Interface.C.Strings

a-calend.ads		package Calendar
a-finali.ads		package Ada.Finalization (for destructors 
etc)

a-string.ads		package Ada.Strings
a-strbou.ads		package Ada.Strings.Bounded