TADS 3 is designed for easy portability to a wide variety of platforms. The source code is written in ANSI C++, and is very conservative in its use of C++ languages features; the code does not use templates, exceptions, or run-time type information, and limits itself to the standard C run-time library.
Different operating systems have a tendency to disagree on the most trivial details. One of these pointless variations that causes a lot of trouble is "newline" conventions: each OS has its own way of signaling the end of a line of text in files such as C source and header files. In almost every case, the end of a line of text is indicated by some combination of the special characters with ASCII values 10 and 13, known respectively as "line feed" or "LF", and "carriage return" or "CR". MS-DOS uses the sequence CR-LF; Unix uses just LF; Macintosh uses just CR; and some system somewhere probably uses LF-CR.
In many cases, systems are tolerant of "foreign" conventions, but sometimes the wrong conventions will confuse compilers and other tools. If you run into any mysterious compiler errors, or your text editor or other tools have problems reading or displaying the TADS source files, you might want to try converting the files to your system's newline conventions. One of the easiest ways to do this is usually to use your UNZIP tool's "auto-convert text files" option when you unpack the TADS source archive - on command-line systems, this is usually the "unzip -a" option.
The TADS 3 source code uses the same technique to separate code into portable and OS layers that TADS 2 used. All of the code in the TADS 3 source distribution is portable, except for the files in system-specific subdirectories (such as "win32"). You should be able to use all of the portable code without making any changes to it. Any required changes in the portable code are porting exceptions; you should report them back to me so that I can find a way to merge the changes to correct the problem. There should be no platform-specific #if's or #ifdef's in the portable code - the source in the portable files should be 100% common to all platforms.
TADS 3 uses the identical OS interface layer that TADS 2 used. So, the first thing you need to do to port TADS 3 to a new platform is to obtain the TADS 2 OS interface implementation for that platform. TADS 2 has been widely ported, so there is a good chance that you can use an existing OS layer implementation for your platform. If you're porting to a platform that doesn't have a TADS 2 port, you must create your own TADS 2 OS interface implementation for the platform. Please obtain a copy of the TADS 2 source distribution for full details on how to go about this.
TADS 3 is designed to share the same object files from the TADS 2 OS layer, so you will not need to create a new copy of the OS files. You should instead simply set up your new TADS 3 makefile so that it includes headers from your TADS 2 OS include directory, and links in the "osxxx" object files from your TADS 2 object file directory.
Refer to win32/makefile.vc5 in the source distribution for an example makefile. This makefile is set up for Microsoft Visual C++ on Windows (it'll work on VC++ versions 5 and 6, at least). This is not any kind of scary project file or other machine-generated monstronsity; it's simply a makefile, similar to Unix-style makefiles. The "vc5" extension, by the way, is just my own naming convention to indicate that it's the Visual C++ version of the makefile.
The Windows makefile defines the groups of object files that make up the various executables. In most cases, you will want to configure your own executables in roughly the same way; the only differences should be that you must substitute your OS layer implementation files for the Windows versions - these are the files whose names start with "os".
Makefiles are pretty nasty to read, so I'll provide some pointers on what to look for. The first piece of information you want from the makefile is simply the group of object files that make up each executable. This much is pretty easy to read - look for names of executables followed immediately by a colon - search for "t3make.exe:", for example, to find the compiler executable's build rule. Following this is a long list of object files. These are the object files that make up the executable. All of the object files prefixed with "$(OBJDIR)" are portable executables. The ones prefixed by "$(TADS2OBJDIR)" are the TADS 2 OS layer object files - these are not part of the TADS 3 source distribution because you can get them from the TADS 2 distribution. The object file list ends at the line that starts with "$(LD) $(LDFLAGS)" - this line starts the command specification for the "link" command that builds the executable.
Many of the executables listed in the makefile are for testing purposes only. You don't need to build these (but you certainly can if you want to run some more in-depth testing on your port).
The source file dependencies are mostly straightforward - these follow the executable rules. However, a few source files have special compilation rules - look at the end of the source-to-object dependency rules for the rules that have explicit "$(CC)" command lines listed under the dependencies. For example, the object module "vmrun_d.obj" is compiled from "vmrun.cpp" with a special compile command (the command sets the #define symbol VM_DEBUGGER).