Thun/docs/1. Basic Use of Joy in a Notebook.md

Preamble

First, import what we need.

from joy.joy import run
from joy.library import initialize
from joy.utils.stack import stack_to_string
from joy.utils.pretty_print import TracePrinter

Define a dictionary, an initial stack, and two helper functions to run Joy code and print results for us.

D = initialize()
S = ()


def J(text):
    print stack_to_string(run(text, S, D)[0])


def V(text):
    tp = TracePrinter()
    run(text, S, D, tp.viewer)
    tp.print_()

Run some simple programs

J('23 18 +')

41

J('45 30 gcd')

15

With Viewer

A viewer records each step of the evaluation of a Joy program. The TracePrinter has a facility for printing out a trace of the evaluation, one line per step. Each step is aligned to the current interpreter position, signified by a period separating the stack on the left from the pending expression ("continuation") on the right. I find these traces beautiful, like a kind of art.

V('23 18 +')

      . 23 18 +
   23 . 18 +
23 18 . +
   41 . 

V('45 30 gcd')

                                  . 45 30 gcd
                               45 . 30 gcd
                            45 30 . gcd
                            45 30 . 1 [tuck modulus dup 0 >] loop pop
                          45 30 1 . [tuck modulus dup 0 >] loop pop
   45 30 1 [tuck modulus dup 0 >] . loop pop
                            45 30 . tuck modulus dup 0 > [tuck modulus dup 0 >] loop pop
                         30 45 30 . modulus dup 0 > [tuck modulus dup 0 >] loop pop
                            30 15 . dup 0 > [tuck modulus dup 0 >] loop pop
                         30 15 15 . 0 > [tuck modulus dup 0 >] loop pop
                       30 15 15 0 . > [tuck modulus dup 0 >] loop pop
                       30 15 True . [tuck modulus dup 0 >] loop pop
30 15 True [tuck modulus dup 0 >] . loop pop
                            30 15 . tuck modulus dup 0 > [tuck modulus dup 0 >] loop pop
                         15 30 15 . modulus dup 0 > [tuck modulus dup 0 >] loop pop
                             15 0 . dup 0 > [tuck modulus dup 0 >] loop pop
                           15 0 0 . 0 > [tuck modulus dup 0 >] loop pop
                         15 0 0 0 . > [tuck modulus dup 0 >] loop pop
                       15 0 False . [tuck modulus dup 0 >] loop pop
15 0 False [tuck modulus dup 0 >] . loop pop
                             15 0 . pop
                               15 . 

Here's a longer trace.

V('96 27 gcd')

                                  . 96 27 gcd
                               96 . 27 gcd
                            96 27 . gcd
                            96 27 . 1 [tuck modulus dup 0 >] loop pop
                          96 27 1 . [tuck modulus dup 0 >] loop pop
   96 27 1 [tuck modulus dup 0 >] . loop pop
                            96 27 . tuck modulus dup 0 > [tuck modulus dup 0 >] loop pop
                         27 96 27 . modulus dup 0 > [tuck modulus dup 0 >] loop pop
                            27 15 . dup 0 > [tuck modulus dup 0 >] loop pop
                         27 15 15 . 0 > [tuck modulus dup 0 >] loop pop
                       27 15 15 0 . > [tuck modulus dup 0 >] loop pop
                       27 15 True . [tuck modulus dup 0 >] loop pop
27 15 True [tuck modulus dup 0 >] . loop pop
                            27 15 . tuck modulus dup 0 > [tuck modulus dup 0 >] loop pop
                         15 27 15 . modulus dup 0 > [tuck modulus dup 0 >] loop pop
                            15 12 . dup 0 > [tuck modulus dup 0 >] loop pop
                         15 12 12 . 0 > [tuck modulus dup 0 >] loop pop
                       15 12 12 0 . > [tuck modulus dup 0 >] loop pop
                       15 12 True . [tuck modulus dup 0 >] loop pop
15 12 True [tuck modulus dup 0 >] . loop pop
                            15 12 . tuck modulus dup 0 > [tuck modulus dup 0 >] loop pop
                         12 15 12 . modulus dup 0 > [tuck modulus dup 0 >] loop pop
                             12 3 . dup 0 > [tuck modulus dup 0 >] loop pop
                           12 3 3 . 0 > [tuck modulus dup 0 >] loop pop
                         12 3 3 0 . > [tuck modulus dup 0 >] loop pop
                        12 3 True . [tuck modulus dup 0 >] loop pop
 12 3 True [tuck modulus dup 0 >] . loop pop
                             12 3 . tuck modulus dup 0 > [tuck modulus dup 0 >] loop pop
                           3 12 3 . modulus dup 0 > [tuck modulus dup 0 >] loop pop
                              3 0 . dup 0 > [tuck modulus dup 0 >] loop pop
                            3 0 0 . 0 > [tuck modulus dup 0 >] loop pop
                          3 0 0 0 . > [tuck modulus dup 0 >] loop pop
                        3 0 False . [tuck modulus dup 0 >] loop pop
 3 0 False [tuck modulus dup 0 >] . loop pop
                              3 0 . pop
                                3 .