Replacing Functions in the Dictionary

For now, there is no way to define new functions from within the Joy language. All functions (and the interpreter) all accept and return a dictionary parameter (in addition to the stack and expression) so that we can implement e.g. a function that adds new functions to the dictionary. However, there’s no function that does that. Adding a new function to the dictionary is a meta-interpreter action, you have to do it in Python, not Joy.

from notebook_preamble import D, J, V

A long trace

V('[23 18] average')
                                  . [23 18] average
                          [23 18] . average
                          [23 18] . [sum 1.0 *] [size] cleave /
              [23 18] [sum 1.0 *] . [size] cleave /
       [23 18] [sum 1.0 *] [size] . cleave /
       [23 18] [sum 1.0 *] [size] . [i] app2 [popd] dip /
   [23 18] [sum 1.0 *] [size] [i] . app2 [popd] dip /
[23 18] [[sum 1.0 *] [23 18]] [i] . infra first [[size] [23 18]] [i] infra first [popd] dip /
              [23 18] [sum 1.0 *] . i [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                          [23 18] . sum 1.0 * [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                               41 . 1.0 * [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                           41 1.0 . * [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                             41.0 . [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                   41.0 [[23 18]] . swaack first [[size] [23 18]] [i] infra first [popd] dip /
                   [23 18] [41.0] . first [[size] [23 18]] [i] infra first [popd] dip /
                     [23 18] 41.0 . [[size] [23 18]] [i] infra first [popd] dip /
    [23 18] 41.0 [[size] [23 18]] . [i] infra first [popd] dip /
[23 18] 41.0 [[size] [23 18]] [i] . infra first [popd] dip /
                   [23 18] [size] . i [41.0 [23 18]] swaack first [popd] dip /
                          [23 18] . size [41.0 [23 18]] swaack first [popd] dip /
                          [23 18] . 0 swap [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                        [23 18] 0 . swap [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                        0 [23 18] . [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
               0 [23 18] [pop ++] . step [41.0 [23 18]] swaack first [popd] dip /
                    0 23 [pop ++] . i [18] [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                             0 23 . pop ++ [18] [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                                0 . ++ [18] [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                                1 . [18] [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                           1 [18] . [pop ++] step [41.0 [23 18]] swaack first [popd] dip /
                  1 [18] [pop ++] . step [41.0 [23 18]] swaack first [popd] dip /
                    1 18 [pop ++] . i [41.0 [23 18]] swaack first [popd] dip /
                             1 18 . pop ++ [41.0 [23 18]] swaack first [popd] dip /
                                1 . ++ [41.0 [23 18]] swaack first [popd] dip /
                                2 . [41.0 [23 18]] swaack first [popd] dip /
                 2 [41.0 [23 18]] . swaack first [popd] dip /
                 [23 18] 41.0 [2] . first [popd] dip /
                   [23 18] 41.0 2 . [popd] dip /
            [23 18] 41.0 2 [popd] . dip /
                     [23 18] 41.0 . popd 2 /
                             41.0 . 2 /
                           41.0 2 . /
                             20.5 .

Replacing size with a Python version

Both sum and size each convert a sequence to a single value.

 sum == 0 swap [+] step
size == 0 swap [pop ++] step

An efficient sum function is already in the library. But for size we can use a “compiled” version hand-written in Python to speed up evaluation and make the trace more readable.

from joy.library import SimpleFunctionWrapper
from joy.utils.stack import iter_stack


@SimpleFunctionWrapper
def size(stack):
    '''Return the size of the sequence on the stack.'''
    sequence, stack = stack
    n = 0
    for _ in iter_stack(sequence):
        n += 1
    return n, stack

Now we replace the old version in the dictionary with the new version, and re-evaluate the expression.

D['size'] = size

A shorter trace

You can see that size now executes in a single step.

V('[23 18] average')
                                  . [23 18] average
                          [23 18] . average
                          [23 18] . [sum 1.0 *] [size] cleave /
              [23 18] [sum 1.0 *] . [size] cleave /
       [23 18] [sum 1.0 *] [size] . cleave /
       [23 18] [sum 1.0 *] [size] . [i] app2 [popd] dip /
   [23 18] [sum 1.0 *] [size] [i] . app2 [popd] dip /
[23 18] [[sum 1.0 *] [23 18]] [i] . infra first [[size] [23 18]] [i] infra first [popd] dip /
              [23 18] [sum 1.0 *] . i [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                          [23 18] . sum 1.0 * [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                               41 . 1.0 * [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                           41 1.0 . * [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                             41.0 . [[23 18]] swaack first [[size] [23 18]] [i] infra first [popd] dip /
                   41.0 [[23 18]] . swaack first [[size] [23 18]] [i] infra first [popd] dip /
                   [23 18] [41.0] . first [[size] [23 18]] [i] infra first [popd] dip /
                     [23 18] 41.0 . [[size] [23 18]] [i] infra first [popd] dip /
    [23 18] 41.0 [[size] [23 18]] . [i] infra first [popd] dip /
[23 18] 41.0 [[size] [23 18]] [i] . infra first [popd] dip /
                   [23 18] [size] . i [41.0 [23 18]] swaack first [popd] dip /
                          [23 18] . size [41.0 [23 18]] swaack first [popd] dip /
                                2 . [41.0 [23 18]] swaack first [popd] dip /
                 2 [41.0 [23 18]] . swaack first [popd] dip /
                 [23 18] 41.0 [2] . first [popd] dip /
                   [23 18] 41.0 2 . [popd] dip /
            [23 18] 41.0 2 [popd] . dip /
                     [23 18] 41.0 . popd 2 /
                             41.0 . 2 /
                           41.0 2 . /
                             20.5 .