ICE-9 is a simple stack-based virtual machine, containing the following instructions.

c/n -- push constant at index n to the stack

e -- pop and echo the top item on the stack

+ -- pop the top two elements on the stack, and push their sum

r -- return, or exit if at bottom of the call stack (REQUIRED AT END OF PROGRAM)

= -- push 1 if the top two elements are equal, 0 otherwise

j/n -- set PC to n if top of stack (popped) equals 1

g/n -- goto n

x/n -- call subroutine at n, pushing a new stack frame

s/n -- set variable n to the value at the top of the stack

v/n -- push the value of variable n

* -- multiple the top two elements, pushing their product

- -- subtract the top two elements, pushing their difference

> -- greater than (2nd greater than first)

< -- less than (2nd less than first)

| -- or

& -- and

! -- not

% -- modulo

Hydro is the primary implementation of the ICE-9 virtual machine, written in the Liquid templating language.

Freon is an implementation of the ICE-9 virtual machine written in Rust for easier debuging.

Any difference in behaviour between Hydro and Freon is an implementation error.

Plasma is a langage that compiles to ICE-9 assembly, which can then be interpreted by liquid.

Here is some sample code. Note that the syntax is highly unstable. This code has been tested and runs successfully when compiled / interpreted.

candidate = 2;

while candidate < 1000 {
  prime? = 1;
  divisor = 2;

  while divisor < candidate {
    if (candidate % divisor) == 0 {
      prime? = 0;
    }
    divisor = divisor + 1;
  }

  if prime? {
    echo candidate;
  }

  candidate = candidate + 1;
}