Chelodina

Chelodina is a transpiler that converts LOGO:

TO triangle :length
  REPEAT 3 [ FORWARD :length RIGHT 120 ]
END

TO flower :length :count
  REPEAT 150 [
    triangle :length
    RIGHT 360 / :count
  ]
END

TO web
  REPEAT 6 [ flower 150 18 ]
END

web

Into Python:

import turtle


def triangle(p_length):
    for _ in range(3):
        turtle.forward(p_length)
        turtle.right(120.0)


def flower(p_length, p_count):
    for _ in range(150):
        triangle(p_length)
        turtle.right(360.0 / p_count)


def web():
    for _ in range(6):
        flower(150.0, 18.0)


web()
turtle.done()

Installation

pip install chelodina

Usage

usage: chelodina [-h] --input INPUT [--run]

arguments:
  -h, --help     show this help message and exit
  --input INPUT  Logo source file
  --run          Run the transpiled code

There's some ready examples to try if you clone the repository:

chelodina --input examples/example1.logo

You can also trigger the program to run in a GUI:

chelodina --input examples/example1.logo --run

Status

• Implemented:
  • Motion functions: FORWARD, BACK, LEFT, RIGHT, SETPOS, SETX, SETY, SETHEADING, SETH, HOME
  • Screen functions: DONE, CLEARSCREEN
  • Control structures: REPEAT
  • Function calls and definitions with optional parameters
  • Binary operations

This is still on an early stage, I focused on making some examples work. Functions with similar structure are trivial to implement, but I want to focus on improving the tests first.

For grammar reference look at grammar.bnf.

Known quirks

• Validations for a valid AST (e.g. to make sure a function parameter exists before trying to use it on a statement) are not user friendly yet. I suggest double-checking your programs elsewhere first.
• Only tested on Python 3.6+ so far.

Development

Use pipenv to install dependencies:

pipenv install --dev

Running tests

Run tests with:

pipenv run tests

Automatically run tests after detecting changes with:

pipenv run tests-watch

Debug

• The easy way is to write tests to debug your code. Feel free to use assert False where necessary.
• If you need to run tests along anything that sends to or needs the standard output (a debugger like pdb or pudb), you'll need to run pytest directly: pytest --capture=no.
• There's a library to pretty-print your AST in the utils package. Usage example:

from chelodina import compiler
from chelodina.utils.debug import parseprint

logo_code = """
to myfunction
  forward 51.0
  left 91
end
"""

parsed_ast = compiler.get_ast(logo_code)
parseprint(parsed)

And you'll see the resulting AST:

Module(body=[
    Import(names=[
        alias(name='turtle', asname=None),
      ]),
    FunctionDef(name='myfunction', args=arguments(args=[], vararg=None, kwonlyargs=[], kw_defaults=[], kwarg=None, defaults=[]), body=[
        Expr(value=Call(func=Attribute(value=Name(id='turtle', ctx=Load()), attr='forward', ctx=Load()), args=[
            Num(n=51.0),
          ], keywords=[])),
        Expr(value=Call(func=Attribute(value=Name(id='turtle', ctx=Load()), attr='left', ctx=Load()), args=[
            Num(n=91.0),
          ], keywords=[])),
      ], decorator_list=[], returns=None),
    Expr(value=Call(func=Attribute(value=Name(id='turtle', ctx=Load()), attr='done', ctx=Load()), args=[], keywords=[])),
  ])

Code style

I use black for code formatting, please install the pre-commit hook before doing a PR. This will be enforced with a linter check in the future.

You can run the command manually too:

black .

Not required, but if you install EditorConfig in your editor of choice it will make your life easier.