From Newsgroup: comp.lang.postscript

GXScript <https://bitbucket.org/ldo17/gxscript> offers Python-style
generator functions, e.g. the following generates all permutations of
items in the array that is passed to it as its argument:

/permute
# list permute raA iterator
# given an array of objects, returns an iterator which will
# return another permutation of those objects each time it
# is nextrCOed.
{
/the_list exch ldef
{
the_list length 0 eq
{ # ifelse
[] yield
}
{ # ifelse
0 1 the_list length 1 sub
{ # for
/i exch ldef
/sublist the_list length 1 sub array ldef
sublist 0 the_list 0 i getinterval putinterval
sublist i the_list i 1 add the_list length 1 sub i sub getinterval putinterval
sublist permute
{ # forall
/subresult exch ldef
/result the_list length array ldef
result 0 the_list i get put
result 1 subresult putinterval
result yield
}
forall
}
for
}
ifelse
}
iter
}
ddef # permute

The rCLforallrCY function accepts the result of a generator call as an iterable, so

[1 2 3] permute {=} forall

produces output

[1 2 3]
[1 3 2]
[2 1 3]
[2 3 1]
[3 1 2]
[3 2 1]
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