Tomo Library/Module Design

There are two ways to "import" code that is defined elsewhere: local files from the same project and shared library objects from another project. The first type of import (local files) is necessary for splitting large projects into smaller components for ease of understanding and compilation speed. The second type of import (shared libraries) is to allow you to install third party libraries or frameworks that can be used across many projects.

Local Imports

To see how local imports work, let's look at a simple file:

// File: foo.tm
my_variable := 123

When this file is compiled to a static object file by tomo -c foo.tm, it produces the following C header file and C source file:

// File: foo.tm.h
#pragma once
#include <tomo/tomo.h>

extern Int_t foo$my_variable;

// File: foo.tm.c
#include <tomo/tomo.h>
#include "foo.tm.h"

Int_t foo$my_variable = I64(123);

Notice that the symbols defined here (foo$my_variable) use a file-based prefix that includes a dollar sign. C compilers support an extension that allows dollar signs in identifiers, and this allows us to use guaranteed-unique prefixes so symbols from one file don't have naming collisions with symbols in another file.

The C file is compiled by invoking the C compiler with something like: cc <flags...> -c foo.tm.c -o foo.tm.o

Now, what happens if we want to use the compiled object file?

// File: baz.tm
foo := use ./foo

func say_stuff():
    say("I got {foo.my_variable} from foo")

func main():
    say_stuff()

If I want to run baz.tm with tomo baz.tm then this transpiles to:

// File: baz.tm.h
#pragma once
#include <tomo/tomo.h>
#include "./foo.tm.h"

void baz$say_stuff();
void baz$main();

// File: baz.tm.c
#include <tomo/tomo.h>
#include "baz.tm.h"

public void baz$say_stuff()
{
  say(CORD_all("I got ", Int$as_text(&foo$my_variable, no, &$Int), " from foo"));
}

public void baz$main()
{
    baz$say_stuff();
}

Then baz.tm.o is compiled to a static object with cc <flags...> -c baz.tm.c -o baz.tm.o.

Next, we need to create an actual executable file that will invoke baz$main() (with any command line arguments). To do that, we create a small wrapper program:

// File: /tmp/program.c
#include <tomo/tomo.h>
#include "baz.tm.h"
 
int main(int argc, char *argv[])
{
    tomo_init();
    if (argc > 1)
        errx(1, "This program doesn't take any arguments.");
    baz$main();
    return 0;
}

This program is compiled with the already-built object files to produce an executable binary called foo like this: cc <flags...> /tmp/program.c foo.tm.o baz.tm.o -o baz

Finally, the resulting binary can be executed to actually run the program!

Shared Library Imports

Now, what's the story with shared library imports? The equivalent process for C is to create a .so or .dll file. In order to build a shared library, you run the command tomo -s=qux.1.2.3 file1.tm file2.tm.... Each specified file will have its .o static object file compiled, along with its dependencies, and all of the resulting .o files will be linked together by tomo with a command like cc <flags...> -Wl,-soname=libqux.1.2.3.so -shared file1.tm.o file2.tm.o dep1.tm.o ... -o libqux.1.2.3.so. The specified files must not define the same public symbols as each other, since foo will now be treated as a single namespace that holds all the symbols from each of the given files.

Symbol Uniqueness

In the future, each of these symbols will be given an extra prefix to prevent namespace collisions and a standalone header file will be built that defines every public symbol in the library in a way that a C compiler can understand. In our example, running tomo -s=qux.1.2.3 foo.tm baz.tm would produce a header file like this:

#pragma once
#include <tomo.h>

extern Int_t qux$1$2$3$foo$my_variable;
extern void qux$1$2$3$baz$say_stuff();

Installing

Now, the components necessary to install this shared library on your computer are these:

The .so file, installed in a standard location. In our case, we will default to ~/.local/share/tomo/lib/libqux.so
The standalone .h file, installed in a standard location. We default to ~/.local/share/tomo/include/qux.h
All of the source .tm files (which store type information necessary for tomo to understand what's being imported. These will be installed to ~/.local/share/tomo/src/qux/

Using Shared Libraries

To use a shared library, write a statement like use qux with an unqualified name (i.e. not an absolute or relative path like /qux or ./qux). When a program uses a shared library, that shared library gets dynamically linked to the executable when compiling, and all of the necessary symbol information is read from the source files during compilation.

Library Versioning

In order to accommodate multiple versions of the same shared libraries on a system, users may specify a library version when compiling, for example: tomo -s qux.1.2.3 foo.tm baz.tm During installation, symlinks are created to map less specific version numbers to more specific version numbers. For example, when installing qux.1.2.3, links are created:

~/.local/share/lib/tomo/libqux.1.2.so -> ~/.local/share/lib/tomo/libqux.1.2.3.so
~/.local/share/lib/tomo/libqux.1.so -> ~/.local/share/lib/tomo/libqux.1.2.3.so
~/.local/share/lib/tomo/libqux.so -> ~/.local/share/lib/tomo/libqux.1.2.3.so
And so on for include/tomo/libqux.1.2.3.h and src/tomo/qux.1.2.3/

If there are multiple versions (e.g. 1.2.3 and 1.3.0), then links point at the highest-numbered version with the necessary prefix. In this case, qux -> qux.1.3.0, qux.1 -> qux.1.3.0, qux.1.3 -> qux.1.3.0, and qux.1.2 -> qux.1.2.3.

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