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Generators In GXScript

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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 → iterator
      # given an array of objects, returns an iterator which will
      # return another permutation of those objects each time it
      # is next’ed.
      {
        /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 “forall” 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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Generators In GXScript Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-09-27 03:34 +0000

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