A (currently) unnamed programming language

This is a programming language prototype that I intend to use for experimentation with some language features I have not seen anywhere else.

Interesting features

Step-by-step execution

If a language is implemented as a virtual machine, and such a virtual machine is implemented in a way that allows having more than one instance at a runtime (meaning, no global variables are used), it should be possible to allow programs to spawn child VMs and drive their execution. In order to instantiate a child VM to evaluate, prefix it with spawn keyword, that will evaluate to a VM handle. The following functions can be applied to such a handle:

• step makes an execution step, returning a boolean flag indicating whether the execution has finished.
• extract returns the result value if VM has finished its execution, halting an interpreter otherwise.
• stack returns a copy of argument's stack.

For example, we can use this feature to trace stack's contents the VM evaluates an expression:

fun main(): int {
    stepwise(spawn 2 * (3 + 4));
    return 0;
}

fun stepwise(v: vm<int>): int {
    val stopped = step(v);
    debug stack(v);
    if (stopped) {
        return extract(v);
    } else {
        return stepwise(v);
    }
}

Output:

[2]
  v => vm<addr=0>
  stack(v) => [2]
[2, 3]
  v => vm<addr=0>
  stack(v) => [2, 3]
[2, 3, 4]
  v => vm<addr=0>
  stack(v) => [2, 3, 4]
[2, 7]
  v => vm<addr=0>
  stack(v) => [2, 7]
[14]
  v => vm<addr=0>
  stack(v) => [14]

Debug expressions

Debug output is probably the most frequent tool used to understand a program's behaviour. Debug expressions in this prototype is super-powered print function, the superpower being that its evaluation will print out every single intermediate result as well.

For example, consider you have a function like this:

fun factorial(x: int): int {
    if (x == 0 || x == 1) {
        return 1;
    }
    return debug x * factorial(x - 1);
}

The debug expression here would produce the following output:

2
  x => 2
  x - 1 => 1
  factorial(x - 1) => 1
  x * factorial(x - 1) => 2
6
  x => 3
  x - 1 => 2
  factorial(x - 1) => 2
  x * factorial(x - 1) => 6
24
  x => 4
  x - 1 => 3
  factorial(x - 1) => 6
  x * factorial(x - 1) => 24
120
  x => 5
  x - 1 => 4
  factorial(x - 1) => 24
  x * factorial(x - 1) => 120

Boring features

• Assignments
• If-statements
• Arithmetic and boolean expressions
• Local variables
• Recursive functions
• Lists

License

Apache 2