The Smol Programming Language and Documentation

A full description of Smol can be found here.

I have been designing Smol since Spring of 2017. My mission is to create a programming language that rigidly enforces the conventions that I have found to be helpful in designing maintainable software. These conventions include

• Statically checked functional correctness
• Explicitness
• Immutability
• Totally defined behavior

The Smol Compiler, smolc

smolc is a highly-portable compiler for the toy programming language I call Smol that emits standard-conforming ISO C99. Smol is a pure, statically-typed, procedural programming language that includes classes, interfaces, tagged unions, and generics.

Smol also includes a verification framework that allows assertions to be checked statically with zero runtime cost. This analysis is mostly sound; programs written in Smol do not reach error states.

Hello world!

// Every Smol file begins with a "package" declaration, which is a namespace.
package hello;

// You must explicitly import types defined in other files.
import core;

// This class called `HelloWorld` defines a static function called `main`,
// which is the entry point of this hello world program.
class HelloWorld {
	static main!() Unit {
		// Invoke a static action on the core:Out type.
		// The `!` indicates that the function is not pure.
		do core:Out.println!("Hello world!");

		// Statically checked assertions can be embedded in your code
		assert (1 + 2) == 3;
	}
}

Installing the Smol compiler

These instructions explain what you need to run smolc and the compiler tests.

First, install Lua 5.1, Lua 5.2, or Lua 5.3. Lua may already be installed on your machine! $ lua -v will print the installed version.

Next, clone this repository.

$ git clone https://github.com/CurtisFenner/smol-builder.git
$ cd smol-builder

The compiler does not need to be built or prepared in any way and it does not have any dependencies other than Lua 5.1/5.2/5.3.

Using the Smol compiler

You can invoke the compiler directly by listing all .smol files that should be compiled and indicating the main class:

$ lua src/compiler.lua --sources tests-positive/runtime/hello-world/test.smol --main test:Test

This produces a C99 output.c file in the current directory that you can compile with your favorite C compiler:

$ gcc -std=c99 -pedantic output.c -o smol-hello-world
$ ./smol-hello-world
Hello world!
Hello
	world!
こんにちは世界
$

Running the Smol compiler tests

The tests have a few extra dependencies:

• You need to have ls available in your path (Cygwin/MinGW will work on Windows)
• Your installation of Lua 5.1/5.2/5.3 must support io.popen (most installations of Lua support io.popen by default)
• You need a version of gcc installed in your path that supports pedantic C99

To run all the tests, run the following from the smol-builder directory:

$ lua test.lua

To only run certain tests, include a filter substring as the first argument to the test script:

$ lua test.lua hello

NOTE: This produces C code and then compiles and executes that C code. Compiler bugs are inevitable, exercise caution!

VSCode Plugin

The VSCode extension can be found here: https://marketplace.visualstudio.com/items?itemName=curtisfenner.smolcomp.

This extension provides syntax highlighting and red-underlining of errors. Configure it by pointing it to the src/compiler.lua file in the cloned folder.

Author

Curtis Fenner, undergraduate at University of Michigan, 2014 - 2018.