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 •