CompSci 308 : Spring 2025

Cell Society: Darwin Simulator

This language was invented by Nick Parlante at Stanford University where it used to be the final assignment for CS106B (their version of CompSci 101).

Create an interactive simulator for a world populated by a number of creatures, showing each creature's current species, location, and orientation, to see how they interact together (and perhaps which species dominates!).

A creature's species is determined by the program it executes on each step of the simulation (so all creatures of the species behave the same way by running the same program although they may each be at a different instruction of their program). A step of the simulation is completed when all non-infected creatures have run one step of their program (i.e., if a creature is infected during a step, then it does not get a chance to run its new program).

During a simulation step, a creature may look in front of itself to see what’s there and then take one action. Thus a program may evaluate any number of IF or GO instructions in a single step. The step ends when the program executes an action instruction (one of MOVE, LEFT, RIGHT, or INFECT). The program starts the subsequent simulation step at the next instruction after the last one executed or starts the program over from the first instruction.

There is one parameter for this model:

nearbyAhead: sets the size of the "neighborhood", the number of cells ahead a creature can see

Example

This is an example of a typical program:

Program Notes Reference
# Flytrap species
ifenemy 4
left 90
go 1
infect 12
go 1
If a creature is ahead nearby, go to instruction 4
Turn left 90 degrees
Go back to instruction 1
Infect the other creature for 5 simulation steps
Go back to instruction 1

Instruction 1
Instruction 2
Instruction 3
Instruction 4
Instruction 5

Program	Notes	Reference
# Flytrap species ifenemy 4 left 90 go 1 infect 12 go 1	If a creature is ahead nearby, go to instruction 4 Turn left 90 degrees Go back to instruction 1 Infect the other creature for 5 simulation steps Go back to instruction 1	Instruction 1 Instruction 2 Instruction 3 Instruction 4 Instruction 5

More examples are given here. You are expected to make your own example files as well (including ones with syntactically incorrect programs).

Commands

Name Description

MOVE pixels
MV pixels Move creature forward by the given pixels in the direction it is facing.
If moving forward would put the creature outside the world's boundaries (if any) or cause it to land on another creature, then this instruction does nothing.

LEFT degrees
LT degrees Turn creature in place left by the given degrees

RIGHT degrees
RT degrees Turn creature in place right by the given degrees

INFECT steps
INF steps Change a creature of any different species (an enemy) into your species if it is in the space nearby ahead for the given number of simulation steps
When a creature is infected, it changes its internal program to the same as the infecting creature (i.e., it becomes one of them) and resets its steps count
When the number of simulation steps is reached, the creature reverts back to its most recent previous species and retains that program until it is infected again
If there is no creature in the space nearby ahead, then this instruction does nothing

IFEMPTY instruction
EMP? instruction Perform the given instruction next only if the space nearby ahead of the creature is empty and inside the world's boundary;
otherwise, go on with the next instruction

IFWALL instruction
WL? instruction Perform the given instruction next only if the space nearby ahead of the creature is the world's boundary;
otherwise, go on with the next instruction

IFSAME instruction
SM? instruction Perform the given instruction next only if the space nearby ahead of the creature is occupied by a creature of the same species;
otherwise, go on with the next instruction

IFENEMY instruction
EMY? instruction Perform the given instruction next only if the space nearby ahead of the creature is occupied by a creature of any different species;
otherwise, go on with the next instruction

IFRANDOM instruction
RND? instruction Perform the given instruction next half of the time (otherwise continue with the next instruction half of the time)
This allows some creatures to exercise what might be called the rudiments of “free will”

GO instruction Perform the given instruction next, rather than the following instruction (if present)

Name	Description
MOVE pixels MV pixels	Move creature forward by the given pixels in the direction it is facing. If moving forward would put the creature outside the world's boundaries (if any) or cause it to land on another creature, then this instruction does nothing.
LEFT degrees LT degrees	Turn creature in place left by the given degrees
RIGHT degrees RT degrees	Turn creature in place right by the given degrees
INFECT steps INF steps	Change a creature of any different species (an enemy) into your species if it is in the space nearby ahead for the given number of simulation steps When a creature is infected, it changes its internal program to the same as the infecting creature (i.e., it becomes one of them) and resets its steps count When the number of simulation steps is reached, the creature reverts back to its most recent previous species and retains that program until it is infected again If there is no creature in the space nearby ahead, then this instruction does nothing
IFEMPTY instruction EMP? instruction	Perform the given instruction next only if the space nearby ahead of the creature is empty and inside the world's boundary; otherwise, go on with the next instruction
IFWALL instruction WL? instruction	Perform the given instruction next only if the space nearby ahead of the creature is the world's boundary; otherwise, go on with the next instruction
IFSAME instruction SM? instruction	Perform the given instruction next only if the space nearby ahead of the creature is occupied by a creature of the same species; otherwise, go on with the next instruction
IFENEMY instruction EMY? instruction	Perform the given instruction next only if the space nearby ahead of the creature is occupied by a creature of any different species; otherwise, go on with the next instruction
IFRANDOM instruction RND? instruction	Perform the given instruction next half of the time (otherwise continue with the next instruction half of the time) This allows some creatures to exercise what might be called the rudiments of “free will”
GO instruction	Perform the given instruction next, rather than the following instruction (if present)

Notes about a program's syntax:

Commands can be separated by any whitespace (one or more spaces, tabs, or newlines)
Command names are not case sensitive (even though they are shown above only in all capital letters)
Command names can be recognized by either their full or abbreviated name (use the full name when referring to the command in documentation or comments)
Command names can be given in any language supported by the program (even though they are shown above only in English) — like the popular language Scratch and the new language Hedy
Ignore any lines that are empty, i.e., only zero or more spaces, or begin with comment character, "#"
Programs start with instruction 1, comments and blank lines do not count as instructions, there is only one instruction per line

Resources

Regular Expressions, a powerful way to match a variety of strings that share a common, well-defined, pattern
Examples given as property files are here
The original assignment specification
Note, the requirements are slightly different than this project and the implementation notes given do not necessarily agree with modern OO design principles, so they should not be copied without justification.