from textx import metamodel_from_str, get_children_of_type
grammar = """
Model: commands*=DrawCommand;
DrawCommand: MoveCommand | ShapeCommand;
ShapeCommand: LineTo | Circle;
MoveCommand: MoveTo | MoveBy;
MoveTo: 'move' 'to' position=Point;
MoveBy: 'move' 'by' vector=Point;
Circle: 'circle' radius=INT;
LineTo: 'line' 'to' point=Point;
Point: x=INT ',' y=INT;
"""
# We will provide our class for Point.
# Classes for other rules will be dynamically generated.
class Point:
    def __init__(self, parent, x, y):
        self.parent = parent
        self.x = x
        self.y = y
    def __str__(self):
        return "{},{}".format(self.x, self.y)
    def __add__(self, other):
        return Point(self.parent, self.x + other.x, self.y + other.y)
# Create meta-model from the grammar. Provide `Point` class to be used for
# the rule `Point` from the grammar.
mm = metamodel_from_str(grammar, classes=[Point])
model_str = """
    move to 5, 10
    line to 10, 10
    line to 20, 20
    move by 5, -7
    circle 10
    line to 10, 10
"""
# Meta-model knows how to parse and instantiate models.
model = mm.model_from_str(model_str)
# At this point model is a plain Python object graph with instances of
# dynamically created classes and attributes following the grammar.
def cname(o):
    return o.__class__.__name__
# Let's interpret the model
position = Point(None, 0, 0)
for command in model.commands:
    if cname(command) == 'MoveTo':
        print('Moving to position', command.position)
        position = command.position
    elif cname(command) == 'MoveBy':
        position = position + command.vector
        print('Moving by', command.vector, 'to a new position', position)
    elif cname(command) == 'Circle':
        print('Drawing circle at', position, 'with radius', command.radius)
    else:
        print('Drawing line from', position, 'to', command.point)
        position = command.point
print('End position is', position)
# Output:
# Moving to position 5,10
# Drawing line from 5,10 to 10,10
# Drawing line from 10,10 to 20,20
# Moving by 5,-7 to a new position 25,13
# Drawing circle at 25,13 with radius 10
# Drawing line from 25,13 to 10,10
# Collect all points starting from the root of the model
points = get_children_of_type("Point", model)
for point in points:
    print('Point: {}'.format(point))
# Output:
# Point: 5,10
# Point: 10,10
# Point: 20,20
# Point: 5,-7
# Point: 10,10