The Sunder Programming Language
Fix incorrect identifier used in `assert` statement
Replace unnecessary uses of `string_*_fmt` with `string_*_cstr`
Fix incorrect C code generation for ellipsis array list elements and zero-sized function arguments


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#The Sunder Programming Language

Sunder is a modest systems programming language for Unix-like platforms.


Sunder tooling should build and run on any supported machine satisfying the following dependencies:

Supported platforms include:

  • x86-64 Linux
  • ARM64 Linux
  • ARM64 macOS
  • WebAssembly (via Emscripten)

The top-level Dockerfile defines a Debian image with dependencies for native x86-64 Linux development pre-installed. You can build and run the Docker image with:

$ docker buildx build --platform=linux/amd64 --tag sunder .             # Build the image (do this once)
$ docker run --rm --interactive --tty --volume "$(pwd)":/sunder sunder  # Run the image (do this every time)


#Quick Version

To build the compiler, run make.

To execute the test suite and compile the example programs under the examples directory, run make check examples.

#Long Version

The top-level Makefile contains the following important targets:

  • build → Build the compiler (default make target).
  • check → Run the test suite for the language and standard library.
  • examples → Compile the example programs under the examples directory.
  • format → Run clang-format over the compiler sources.
  • clean → Remove build artifacts.

Targets will execute with CC=c99 using release mode CFLAGS by default.

Specific CC/CFLAGS combinations include:

$ make <targets> CFLAGS='$(C99_DBG)'  # POSIX c99 (debug)
$ make <targets> CFLAGS='$(C99_REL)'  # POSIX c99 (release)

$ # Use CC=clang for Clang or CC=gcc for GCC
$ make <targets> CC=clang CFLAGS='$(GNU_DBG)'  # clang/gcc (debug)
$ make <targets> CC=clang CFLAGS='$(GNU_REL)'  # clang/gcc (release)


The install target will install the Sunder toolchain into the directory specified by SUNDER_HOME (default $HOME/.sunder). Run make install with SUNDER_HOME specified as the directory of your choice:

$ make install                          # Install to the default $HOME/.sunder
$ make install SUNDER_HOME=/opt/sunder  # Install to /opt/sunder

Then, add the following snippet to your .profile, replacing $HOME/.sunder with your chosen SUNDER_HOME directory if installing to a non-default SUNDER_HOME location:

export SUNDER_HOME="$HOME/.sunder"
if [ -e "$SUNDER_HOME/env" ]; then
    . "$SUNDER_HOME/env"

Verify that the compiler has been successfully installed by running sunder-compile -h. You may need to source your .profile in new shells until the start of your next login session.

#Using the Sunder Compiler

Sunder programs are compiled with sunder-compile.

import "std";

func main() void {
    std::print_line(std::out(), "Hello, world!");
$ sunder-compile -o hello examples/hello.sunder
$ ./hello
Hello, world!

The -o OUT option may be used to specify the name of the output file. If this option is not provided, the output file will default to the name a.out.

Intermediate files of the form OUT.tmp.* for output program OUT are generated during compilation and subsequently removed after the output file has been created. The -k flag will instruct the compiler not to remove these files.

$ sunder-compile -k -o hello examples/hello.sunder
$ ls hello*
hello  hello.tmp.c

$ SUNDER_CC=emcc SUNDER_ARCH=wasm32 SUNDER_HOST=emscripten sunder-compile -k -o hello.html examples/hello.sunder
$ ls hello*
hello.html  hello.html.tmp.c  hello.js  hello.wasm

The -g flag will instruct the compiler to generate debug information. The use of -g in combination with -k facilitates debugging with GDB and LLDB.

$ sunder-compile -g -k -o hello examples/hello.sunder
$ lldb hello
(lldb) target create "hello"
Current executable set to '/Users/ashn/sources/sunder/hello' (arm64).
(lldb) b std_print_line
Breakpoint 1: where = hello`std_print_line + 32 at hello.tmp.c:25216:9, address = 0x000000010000d24c
(lldb) run
Process 80648 launched: '/Users/ashn/sources/sunder/hello' (arm64)
Process 80648 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x000000010000d24c hello`std_print_line(__sunder_argument_0_writer=__sunder_std_writer @ 0x000000016fdff0c0, __sunder_argument_1_str=(start = "Hello, world!", count = 13)) at hello.tmp.c:25216:9
   25213	__sunder_std_print_line(__sunder_std_writer __sunder_argument_0_writer, __sunder_slice_of_byte __sunder_argument_1_str)
   25214	{
   25215	   // var return: void
-> 25216	   int __sunder_return = /* zero-sized local */0;
   25217	   // var result: std::result[[void, *std::error_info]]
   25218	   __sunder_std_result__void___std_error_info__ __sunder_local_0_result = {/* uninit */0};
   25219	   /// [std/std.sunder:1592] STATEMENT STMT_ASSIGN
Target 0: (hello) stopped.

The following environment variables affect compiler behavior:

SUNDER_CC selects the C compiler to be used when compiling generated C. Currently, SUNDER_CC=clang, SUNDER_CC=gcc, and SUNDER_CC=emcc are supported. If SUNDER_CC is not set, then the default C compiler is used.

SUNDER_CFLAGS is a space-separated list of additional flags passed to the C compiler.

SUNDER_SEARCH_PATH is a colon-separated list of directories specifying the module search path for import and embed statements.

SUNDER_ARCH specifies the target architecture to build for. Currently, SUNDER_ARCH=amd64, SUNDER_ARCH=arm64, and SUNDER_ARCH=wasm32 are supported. If SUNDER_ARCH is not set, then the default architecture specified by sunder-platform arch is used.

SUNDER_HOST specifies the target operating system to build for. Currently, SUNDER_HOST=emscripten, SUNDER_HOST=linux, and SUNDER_HOST=macos are supported. If SUNDER_HOST is not set, then the default host specified by sunder-platform host is used.

#Compiling to WebAssembly

Sunder supports compiling to WebAssembly via Emscripten. When compiling to WebAssembly, specify emcc, wasm32, and emscripten as the C compiler, target architecture, and target host, respectively.

$ SUNDER_CC=emcc \
    SUNDER_CFLAGS="-sSINGLE_FILE --shell-file ${SUNDER_HOME}/lib/sys/sys.wasm32-emscripten.html" \
    SUNDER_ARCH=wasm32 \
    SUNDER_HOST=emscripten \
    sunder-compile -o hello.html examples/hello.sunder
$ firefox --new-window "file://$(realpath hello.html)"

#Using Sunder as a Scripting Language

Sunder can be used for scripting by adding #!/usr/bin/env sunder-run as the first line of a Sunder source file.

#!/usr/bin/env sunder-run
import "std";

func main() void {
    std::print(std::out(), "What is your name?\n> ");

    var result = std::read_line(std::input());
    if result.is_error() {
        std::print_line(std::err(), result.error().*.data);

    var optional = result.value();
    if optional.is_empty() or countof(optional.value()) == 0 {
        std::print_line(std::err(), "unexpected empty input");

    var line = optional.value();
    defer std::slice[[byte]]::delete(line);

    var name = std::ascii::view_trimmed(optional.value());
    std::print_format_line(std::out(), "Nice to meet you {}!", (:[]std::formatter)[std::formatter::init[[typeof(name)]](&name)]);
$ ./examples/greet.sunder
What is your name?
> Alice
Nice to meet you Alice!

#Using Sunder Without Installing

Executing the following commands will create an environment sufficient for Sunder development and experimentation without requiring the Sunder toolchain to be installed.

$ cd /your/path/to/sunder
$ make
$ SUNDER_HOME="$(pwd)"
$ . ./env
$ sunder-run examples/hello.sunder
Hello, world!


Sunder is distributed under the terms of the Apache License (Version 2.0).

See LICENSE for more information.