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. .. code:: ipython2 from notebook_preamble import D, J, V A long trace ------------ .. code:: ipython2 V('[23 18] average') .. parsed-literal:: . [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. .. code:: ipython2 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. .. code:: ipython2 D['size'] = size A shorter trace --------------- You can see that ``size`` now executes in a single step. .. code:: ipython2 V('[23 18] average') .. parsed-literal:: . [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 .