turtle

A toy logo implementation for CS 355 at Washington State University

Introduction

The turtle interpreter is designed to direct a 'turtle' to draw a picture. Commands are read from stdin, and an image is drawn and output to stdout in pgm format.

Files included in this archive

Makefile        Makefile to build project
README.md       This file

interpreter.c   Code to perform ll(1) parse of code

scanner.c       Code to scan for next token, provided by Dr
scanner.h       Wayne Cochran

symtab.code     Symbol table provided by Dr Wayne Cochran
symtab.h

turtle.c        Code to control the turtle for drawing,
turtle.h        provided by Dr Wayne Cochran

code/	          Sample .turtle files containing turtle code

Compiling and Executing

Make is required to compile the project.

In the root directory, type:

make

This will build an executable named turtle that can be used to interpret turtle commands (code) and create images.

Turtle will take commands from stdin and output a pgm image to stdout

Turtle will accept commands directly, and output to file using the following command:

turtle > image.pgm

This will take commands from stdin to draw with the turtle, ctrl-D stops the interpretter and dumps a pgm to image.pgm

Source files can be piped into the interpretter on stdin.

turtle < source.turtle > image.pgm

The above command will generate an image image.pgm specified by the commands in source.turtle

The Turtle Language

The Turtle

The turtle can be commanded to do different things, the commands are listed below:

HOME -- moves the turtle to the origin, facing east

PENUP -- tells the turtle to put it's 'pen' down, drawing where it moves

PENDOWN -- tells turtle to stop drawing

FORWARD expr -- move forward a distance specified by expr

LEFT expr -- rotate expr degrees left

RIGHT expr -- rotate expr degrees right

PUSHSTATE -- record the turtles current state, and save it on the stack

POPSTATE -- recall the top state on the stack

Variables

All variables are floats, initialized to 0.0 the first time they show up in code. They must begin with a letter and can contain letters and numbers, but none of the reserved words.

:= Assignment operator

FOO := 5 assigns a value of 5 to FOO

Expressions

All expressions are infix. The +, -, /, and * symbols are all valid operators that behave as expected. Parentheses may be used to specify precedence. All expressions deal with Variables and literal values.

Examples:

6 + 7
FOO * 5
(5 + 8) * BAR

Boolean expressions

Boolean expressions are a boolean operator with an Expression on either side. Operators are: =, NE, < , LE, >, GE and the Unary operator NOT.

Examples:

5 > FOO
4 NE 1
NOT (5 > 4)

If statements:

IF <bool>
THEN <stmt list>
{ ELSIF <bool> THEN <stmt list> }
[ ELSE <stmt list> ]
FI

For example:

IF <condition> THEN
...
FI

This is the simplest if statement, and performs ... if condition is true.

An ELSE can be added:

IF <condition> THEN
...
ELSE
...
FI

ELSE-IF chains:

IF <condition> THEN
ELSIF <condition> THEN ...
ELSIF <condition> THEN ...

While statements:

WHILE <bool> DO <stmt list> OD

As long as the bool expression is true, this will repeatedly execute the code between DO and OD.

Version Information

Turtle Language Interpretter Version 1.0, released 2/10/11

Matthew Zinke zinkem@gmail.com

Project for CS 355 at Washington State University Taught by Dr Wayne Cochran

zinkem/turtle