# COMP6991 Rust Logo Interpreter Assignment
**Logo Language Overview**
– Logo is a programming language derived from Lisp and others.
– Older programmers often had their first programming experience with Logo.
– Key feature is a “turtle” for drawing by picking up and putting down a pen and moving around.
**Assignment Goals**
– Practice designing and structuring a larger Rust program.
– Focus on modern programming skills and design patterns.
– Have fun creating an aesthetic and interesting application while connecting with programming history.
**Assignment Requirements**
– Build a Logo interpreter that writes to an.svg or.png image using the `unsvg` crate.
– Handle various Logo commands for turtle control, variables, queries, conditionals, and math operations.
– Implement design excellence features for full marks.
## 1. Introduction to the Logo Language
### Tokens
– A token can be a procedure (like a function), a variable (prefixed by `:`), or a value (prefixed by `”`).
– Procedures always take a fixed number of arguments.
– Values in Logo are always strings, but some like `”TRUE”` and `”FALSE”` are interpreted as booleans and some can be parsed as numbers.
### Program Structure
– A logo program consists of lines of text split into tokens by whitespace.
– Lines starting with `//` or empty lines are ignored as comments.
## 2. Introduction to Unsvg
– The assignment uses the `unsvg` crate to generate SVG or PNG images.
– `unsvg::Image` represents an image and has methods like `draw_simple_line`.
– `unsvg::get_end_coordinates` returns where a line drawn from a given point would end.
## 3. How Your Program Will Work
– Produce a program called `rslogo` that takes four arguments: a logo program file (.lg), the output SVG/PNG file path (.svg or.png), image height, and image width.
– Read the logo program, parse and execute it line by line.
– Exit with a non-zero return code and print an error message if there’s an issue.
– Write an SVG or PNG using the `unsvg` crate if there are no issues.
## 4. Design Excellence
– Options for design excellence include making beautiful errors, achieving 80% test coverage, using a parser combinator library, creating a facility for language extensions, building a zero-copy program, contributing to the `unsvg` library, or building a transpiler.
– Markers will consider a reasonable attempt at one of these tasks as sufficient.
## 5. The Tasks To Complete
### Part 1: Turtle Control (20%)
– Control the “turtle” which is like an invisible pen that can draw on the image.
– Turtle starts “up” (not drawing) in the center of the screen facing straight up.
– Commands include `PENUP`, `PENDOWN`, `FORWARD`, `BACK`, `LEFT`, `RIGHT`, `SETPENCOLOR`, `TURN`, `SETHEADING`, `SETX`, `SETY`.
– Turtle can go off the image without causing an error.
### Part 2: Variables and Queries (20%)
– Implement the `MAKE` command to create and assign variables.
– Implement the `ADDASSIGN` command for variable increment.
– Support “queries” like `XCOR`, `YCOR`, `HEADING`, `COLOR`.
### Part 3: IFs, WHILE, [ ] (20%)
– Implement `IF EQ` and `WHILE EQ` commands for conditional execution and looping.
### Part 4: Implementing Maths and Comparisons using a Stack (20%)
– Implement operations in Polish Notation like `EQ`, `NE`, `GT`, `LT`, `AND`, `OR`, `+`, `-`, `*`, `/`.
– Implement stack operations for `IF` and `WHILE`.
### Part 5: Logo Defined Procedures (20%)
– Implement procedures analogous to functions in other languages.
– Procedures are defined with a line starting with `TO`, followed by the procedure name and arguments, and ending with `END`.
## 6. Common Questions
### Design Approaches
– Line-by-line approach: Execute each line in turn while storing more data and state.
– Parse then execute approach: Convert the text into an Abstract Syntax Tree and read from it.
### Planning
– A happy middle is suggested: think about the approach and read through the assignment without spending more than 30 minutes planning.
### Using AI
– Permitted uses of AI include seeking help with concepts, pattern matching, generating skeletons, and writing tests.
## 7. Other Information
### Submission
– See instructions at the bottom of the page.
### Using Other Crates
– Can use crates from crates.io under certain conditions.
### Marking Scheme
– Marked on Mechanical Style (10%), Functional Correctness (40%), and Idiomatic Design (50%).
## 8. Formal Stuff
– Assignment is individual.
– No joint work or sharing of code allowed.
– Use of code-synthesis tools is permitted but with caution.
– Submit work by running `6991 give-crate` by Week 7 Wednesday 17:00:00.