Linking & FFI

Extern functions (calling native code)

@link("kernel32.dll");
extern fn GetTickCount() -> u32;
extern fn Sleep(ms: u32);

extern fn declares a function that lives in a native library. The compiler generates a calling convention trampoline automatically.

Custom symbol names

If the native symbol differs from the tape function name:

@link("user32.dll");
extern("MessageBoxA") fn message_box(hwnd: *u8, text: *u8, caption: *u8, flags: u32) -> i32;

The extern("symbol") form specifies the exact linker symbol to resolve.

@link directive

Declares which native library to link against:

@link("user32.dll");         // Windows DLL
@link("opengl32.dll");       // Windows DLL
@link("libSystem.B.dylib");  // macOS system library
@link("libc.so.6");          // Linux shared library

All extern fn declarations following a @link are resolved from that library. Multiple @link directives can appear in one file.

Exported functions (callable from native code)

@export
pub fn tape_init(config: *u8) -> i32 {
    return 0;
}

@export marks a function for inclusion in the output’s export table (DLL exports on Windows, .sto vtable on Uusi).

Custom export symbol:

@export("my_custom_name")
pub fn internal_name() -> i32 {
    return 42;
}

Link checking

The compiler verifies at build time that @link libraries exist and all extern symbols resolve (on the host platform). Skip with --skip-link-check for cross-compilation.

Cross-module linking

Tape modules link to each other automatically through the import system. The compiler:

1. Parses all imported modules recursively
2. Injects extern stubs for all pub declarations with qualified names (module.fn_name)
3. Resolves cross-module calls at link time

Internal symbol naming uses dot-separated qualified names (io.println, str.len) and double-underscore for methods (Button__paint, Vec2__op_add).

Output formats

DLL output

tape build lib.tape --dll -o mylib.dll

Only functions marked @export appear in the DLL’s export table.

Uusi shared object

tape build lib.tape --sto --target uusi -o mylib.sto

On Uusi, @link externs are resolved at runtime via syscall 23 (library load). The compiler emits thunks that:

1. Load the .sto library
2. Read the vtable pointer from the library handle
3. Jump to the function pointer at the correct vtable slot

Platform-specific linking

Last modified: 2026-05-27 20:22:46 UTC