Syntax to declare variable without assign value

Jou programming language

Jou is an experimental toy programming language. It looks like this:

import "stdlib/io.jou"

def main() -> int:
    puts("Hello World")
    return 0

See the examples and tests directories for more example programs or read the Jou tutorial.

So far, Jou is usable for writing small programs that don't have a lot of dependencies. For example, I solved all problems of Advent of Code 2023 in Jou. See examples/aoc2023 for the code.

Goals:

Minimalistic feel of C + simple Python-style syntax
Possible target audiences:
- People who find C programming fun
- Python programmers who want to try programming at a lower level (maybe to eventually learn C or Rust)
Compatibility with C, not just as one more feature but as the recommended way to do many things
Self-hosted compiler
Eliminate some stupid things in C. For example:
- Many useful warnings being disabled by default
- UB for comparing pointers into different memory areas (as in array <= foo && foo < array+sizeof(array)/sizeof(array[0]))
- negative % positive is negative or zero, should IMO be positive or zero (unless that is a lot slower, of course)
- Strict aliasing
- int possibly being only 16 bits
- long possibly being only 32 bits
- char possibly being more than 8 bits
- char possibly being signed
- char being named char even though it's really a byte
Generics, so that you can implement a generic list (dynamically growing array) better than in C
Compiler errors for most common bugs in C (missing free(), double free(), use after free, etc.)
More keywords (def, decl, forwarddecl)
Enumerated unions = C union together with a C enum to tell which union member is active
Windows support that doesn't suck

Non-goals:

Yet another big language that doesn't feel at all like C (C++, Zig, Rust, ...)
Garbage collection (should feel lower level than that)
Wrapper functions for the C standard library
Wrapper libraries for existing C libraries (should just use the C library directly)
Trying to detect every possible memory bug at compile time (Rust already does it better than I can, and even then it can be painful to use)
Copying Python's gotchas (e.g. complicated import system with weird syntax and much more weird runtime behavior)

Setup

These instructions are for using Jou. The instructions for developing Jou are in CONTRIBUTING.md.

Linux

Install the dependencies:
```
$ sudo apt install git llvm-14-dev clang-14 make
```
Let me know if you use a distro that doesn't have apt, and you need help with this step.

Download and compile Jou.

$ git clone https://github.com/Akuli/jou
$ cd jou
$ make

Run the hello world program to make sure that Jou works:
```
$ ./jou examples/hello.jou
Hello World
```
You can now run other Jou programs in the same way.
(Optional) If you want to run Jou programs with simply jou filename instead of something like ./jou filename or /full/path/to/jou filename, you can add the jou directory to your PATH. To do so, edit ~/.bashrc (or whatever other file you have instead, e.g. ~/.zshrc):
```
$ nano ~/.bashrc
```
Add the following line to the end:
```
export PATH="$PATH:/home/yourname/jou/"
```
Replace /home/yourname/jou/ with the path to the folder (not the executable file) where you downloaded Jou. Note that the ~ character does not work here, so you need to use a full path (or $HOME) instead.

These LLVM/clang versions are supported:

LLVM 11 with clang 11
LLVM 13 with clang 13
LLVM 14 with clang 14

By default, the make command picks the latest available version. You can also specify the version manually by setting the LLVM_CONFIG variable:

$ sudo apt install llvm-11-dev clang-11
$ make clean    # Delete files that were compiled with previous LLVM version
$ LLVM_CONFIG=llvm-config-11 make

MacOS

MacOS support is new. Please create an issue if something doesn't work.

Install Git, make and LLVM 13. If you do software development on MacOS, you probably already have Git and make, because they come with Xcode Command Line Tools. You can use brew to install LLVM 13:
```
$ brew install llvm@13
```

Download and compile Jou.

$ git clone https://github.com/Akuli/jou
$ cd jou
$ make

Run the hello world program to make sure that Jou works:
```
$ ./jou examples/hello.jou
Hello World
```
You can now run other Jou programs in the same way.
(Optional) If you want to run Jou programs with simply jou filename instead of something like ./jou filename or /full/path/to/jou filename, you can add the jou directory to your PATH. To do so, edit ~/.bashrc (or whatever other file you have instead, e.g. ~/.zshrc):
```
$ nano ~/.bashrc
```
Add the following line to the end:
```
export PATH="$PATH:/Users/yourname/jou/"
```
Replace /Users/yourname/jou/ with the path to the folder (not the executable file) where you downloaded Jou. Note that the ~ character does not work here, so you need to use a full path (or $HOME) instead.

NetBSD

Support for NetBSD is still experimental. Please report bugs and shortcomings.

Install the dependencies:
```
# pkgin install bash clang git gmake libLLVM
```
Optionally diffutils can be installed for coloured diff outputs.

Download and compile Jou.

$ git clone https://github.com/Akuli/jou
$ cd jou
$ gmake

Run the hello world program to make sure that Jou works:
```
$ ./jou examples/hello.jou
Hello World
```
You can now run other Jou programs in the same way.
(Optional) If you want to run Jou programs with simply jou filename instead of something like ./jou filename or /full/path/to/jou filename, you can add the jou directory to your PATH. Refer to the manual page of your login shell for exact syntax.

NB: Using Clang and LLVM libraries built as a part of the base system is not currently supported.

64-bit Windows

Go to releases on GitHub. It's in the sidebar at right.
Choose a release (latest is probably good) and download a .zip file whose name starts with jou_windows_64bit_.
Extract the zip file somewhere on your computer.
You should now have a folder that contains jou.exe, lots of .dll files, and subfolders named stdlib and mingw64. Add this folder to PATH. If you don't know how to add a folder to PATH, you can e.g. search "windows add to path" on youtube.
Write Jou code into a file and run jou filename.jou on a command prompt. Try the hello world program, for example.

Updating to the latest version of Jou

Run jou --update. On old versions of Jou that don't have --update, you need to instead delete the folder where you installed Jou and go through the setup instructions above again.

Editor support

Tell your editor to syntax-highlight .jou files as if they were Python files. You may want to copy some other Python settings too, such as how to handle indentations and comments.

If your editor uses a langserver for Python, make sure it doesn't use the same langserver for Jou. For example, vscode uses the Pylance language server, and you need to disable it for .jou files; otherwise you get lots of warnings whenever you edit Jou code that would be invalid as Python code.

For example, I use the following configuration with the Porcupine editor:

[Jou]
filename_patterns = ["*.jou"]
pygments_lexer = "pygments.lexers.Python3Lexer"
syntax_highlighter = "pygments"
comment_prefix = '#'
autoindent_regexes = {dedent = 'return( .+)?|break|pass|continue', indent = '.*:'}

To apply this configuration, copy/paste it to end of Porcupine's filetypes.toml (menubar at top --> Settings --> Config Files --> Edit filetypes.toml).

How does the compiler work?

See CONTRIBUTING.md.

	/*
	After parsing, the AST contains types only where the types were specified
	by the user, e.g. in function declarations. A separate "typing pass" fills
	in the types of all expressions.

	This is a bit weird, but I don't want to duplicate the AST into "typed AST"
	and "untyped AST". I have done that previously in other projects.
	*/

	static LLVMValueRef make_a_string_constant(const struct State st, const char s)
	{
	// https://stackoverflow.com/a/37906139
	LLVMValueRef array = LLVMConstString(s, strlen(s), false);
	LLVMValueRef stack_space_ptr = LLVMBuildAlloca(st->builder, LLVMTypeOf(array), "string_data");
	LLVMBuildStore(st->builder, array, stack_space_ptr);
	LLVMTypeRef string_type = LLVMPointerType(LLVMInt8Type(), 0);
	return LLVMBuildBitCast(st->builder, stack_space_ptr, string_type, "string_ptr");
	}

	# fib40.jou (Jou program)
	declare printf(format: byte*, ...) -> int

	const struct CfVariable *target = build_address_of_expression(st, targetexpr);
	assert(target->type.kind == TYPE_POINTER);

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Jou programming language

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