cmaes / logoturtle

An implementation of the Logo (turtle graphics) language in ocaml

A Logo Interperter in Ocaml (and Javascript)

Try the interperter in your browser

Visit http://cmaes.github.io/logoturtle/

See this page for sample programs and their graphical output.

Installation

The following directions describe how to install the dependencies for running the code locally.

Install OCAML

Use the Real World OCAML installation instructions https://github.com/realworldocaml/book/wiki/Installation-Instructions

On Linux

$ sudo add-apt-repository ppa:avsm/ppa
$ sudo apt-get update
$ sudo apt-get install curl build-essential m4 ocaml opam

Then do

opam init
eval `opam config env`

On Mac

Install Homebrew http://brew.sh.

brew install ocaml
brew install opam

Then do

opam init
eval `opam config env`

Install ocamlfind

opam install ocamlfind

Install the Cairo Ocaml bindings

https://github.com/Chris00/ocaml-cairo

opam install cairo2

Install Dependencies

opam install core
opam install menhir
opam install lwt

Install js_of_ocaml

opam install js_of_ocaml
opam install js_of_ocaml-camlp4

Building the Logo Interperter

There are two different builds of the interperter:

• A interpreter that runs from the command-line and uses Cairo as backend to output .png files from Logo programs

• A interpreter that runs from Javascript and uses a Canvas backend to output graphics from Logo programs in the browser

Building the Command-line Interpreter

Issuing the following command to build both.

make

will build and run a program called logo.native. It creates a file named tree.png that should contain a tree.

To clean up do

make clean

Building the Javascript Interpreter

Issuing the following command

make logoweb.js

will build a Javascript library containing the interpreter. The file index.html shows how this library may be used from Javascript via the interpetLOGO command.

Logo Grammar

I made my own up. But there is one here

logoturtle's Issues

Syntax and runtime errors should be reported in the repl

Write now they just create an exception in the JS console.

Logo grammar has one shift/reduce conflict

This is related to unary minus

Warning: one state has shift/reduce conflicts.
Warning: one shift/reduce conflict was arbitrarily resolved.

Here is parser.conflict

** Conflict (shift/reduce) in state 61.
** Token involved: MINUS
** This state is reached from prog after reading:

ID rev_args_list expr 

** The derivations that appear below have the following common factor:
** (The question mark symbol (?) represents the spot where the derivations begin to differ.)

prog 
command_list EOF 
rev_command_list 
command 
ID args_list 
   rev_args_list 
   (?)

** In state 61, looking ahead at MINUS, shifting is permitted
** because of the following sub-derivation:

rev_args_list expr 
              arith 
              expr . MINUS expr 

** In state 61, looking ahead at MINUS, reducing production
** rev_args_list -> rev_args_list expr 
** is permitted because of the following sub-derivation:

rev_args_list expr // lookahead token appears because expr can begin with MINUS
rev_args_list expr . 

Pattern matching for expression evaluator is not exhaustive

OCaml gives the following error:

File "logoturtle.ml", line 226, characters 22-121:
Warning 8: this pattern-matching is not exhaustive.
Here is an example of a value that is not matched:
(Plus (_, _)|Minus (_, _)|Times (_, _)|Divide (_, _)|Negate _|Or (_, _)|
And (_, _)|Not _|Less (_, _)|Greater (_, _)|Equal (_, _)|NEqual (_, _)|
LessEq (_, _)|GreaterEq (_, _))

But it looks to me like it is covering all the cases.