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_()
J('23 18 +')
41
J('45 30 gcd')
15
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 •