Logo3D

Introduction

Logo3D is a modernized version of the programing language LOGO designed in 1967 by Wally Feurzeig, Seymour Papert, and Cynthia Solomon.

This is part of a project for the Programing Languages class at the Barcelona School of Informatics (FIB UPC) - Q2 2020-21

---

Contents

this language is programmed in python and ANTLR and is composed of various source files:

• logo3d.py is the language's interpreter

• logo3d.g is the language's grammar, defined in ANTLR

• visitior.py is the language's AST visitor, which navigates the Abstract Syntax Tree

• turtle3d.py contains the Turtle3D class, which implements LOGO's turtle

---

Installation

To use Logo3D you must first download the previously mentioned files and install the libraries from requirements.txt using the command:

python -m pip install -r requirements.txt

generate the parser and lexer files using:

antlr4 -Dlanguage=Python3 -no-listener logo3d.g

and finally generate the visitor parent class file using:

antlr4 -Dlanguage=Python3 -no-listener -visitor logo3d.g

Now you can run your own Logo3D programs following the usage below!

---

The Turtle3D class

The Turtle3D class implements a 3D version of the original logo's turtle. This class creates a scene using vpython and draws a red "turtle" (a sphere), that leaves a trail behind by default when moved.

The turtle has methods:

• left(deg), right(deg), up(deg) and down(deg) to change horizontal and vertical direction by deg degrees.
• forward(dist) and backward(dist) to move in said direction dist distance.
• show() and hide() to start or stop leaving a trail respectively.
• color(r, g, b) to define the turtle's trail color by its RGB values.
• home() to move the turtle back to its origin.

---

The Logo3D language

The Logo3D language is defined by the grammar in logo3d.g, the lexer (logo3dLexer.py) and parser (logo3dParser.py) generated by ANTLR-python and the visitor in visitior.py (wich inherits from logo3dVisitor.py, also generated by ANTLR-python).

It implements some very basic programming features, just like the original logo:

• variable assignment with :=

  perimetre  := 2 * 3.1416 * radi
  

• reading from stdin to a variable with >>

  >> radi
  

• writing to stdout from a variable or expression with <<

  << radi
  << 5 * 3 - 2
  

• conditionals with IF _ THEN _ END or IF _ THEN _ ELSE _ END

  IF x == y THEN z := 1 END
  IF x == y THEN z := 1 ELSE z := 2 END
  

• loops with WHILE _ DO _ END or FOR var FROM num TO num DO _ END

  WHILE a > 0 DO a := a / 2 END
  FOR i FROM 1 TO 5 DO i := i + 1 << i END
  

• procedure declaration with PROC name_proc(args) IS _ END

  PROC main(n) IS 
      << n
  END
  

• procedure invocation with name_proc(args)

  PROC write(n) IS
      << n
  END
  
  PROC main(n) IS 
      write(n)
  END
  

  Logo3D natuarlly implements all of Turtle3D's public procedures to control the turtle. These procedures can be called like any other Logo3D procedure:

  PROC main(mida) IS 
      FOR i FROM 1 TO 4 DO
          color(i/12, i/12, i/4)
          forward(mida)
          left(90)
      END
  END
  

a Logo3D program can be executed by using:

python3 logo3d.py program_source_code.l3d args

The main procedure will be executed by default if no other procedure and its arguments is passed by parameters