how to make an interpreter

here's how to make a really simple interpreter:

first, we define our language:

right,# - turn right with the following impulse
foward,# - go forward with the following impulse

then, we create a small program. this should make the object move in a circle.

list program = ["right,5", "forward,10"];

now we need a way to execute the program. we'll use a timer. we'll also set the program counter to 0 (start of program).

state_entry()
{
  program_counter = 0;
  program_length = llGetListLength(program);
  llSetTimerEvent(1);
}

in the timer event we'll process the instructions:

timer()
{
  string instruction = llList2String(program, program_counter);
  llMessageLinked(LINK_SET, 0, instruction, NULL_KEY);
  program_counter = (program_counter + 1) % program_length;
}

so at this point we are firing link messages containing the instruction, e.g. 'right,5'. all that's left is to make the object respond to the messages.

link_message(integer sender_num, integer num, string str, key id)
{
  string tokens = llParseString2List(str, [","], []);
  string token0 = llList2String(tokens, 0);
  if (token0 == "right")
  {
     integer impulse = llList2Integer(tokens, 1);
     llApplyImpulse(<impule, 0, 0>, TRUE);
  }
  else if (token0 == "forward")
  {
     integer impulse = llList2Integer(tokens, 1);
     llApplyImpulse(<0, impulse, 0>, TRUE);
  }
}