eval.py

currentFont = None
typing = ""
items = []

def setup():
    global currentFont
    size(500, 500)
    currentFont = createFont("Courier", 16, True)

def draw():
    global typing
    background(255)
    textFont(currentFont)
    fill(0)
    text(typing, 50, 50)
    for item in items:
        if callable(item):
            try:
                item()
            except Exception as e:
                print e

def keyPressed():
    global typing
    if key == '\r':
        try:
            exec typing
        except Exception as e:
            print e
        typing = ""
    else:
        if isinstance(key, str) or isinstance(key, unicode):
            typing = typing + key