Ruby fiber additional resume -

in example, fiber resumed once more create 1 more output unexpectedly. target print permutation of 1 array of numbers iterating through possibilities recursion , print out result in fiber.

class fiber   def self.wrap     if block_given?       f=fiber.new |*args|          yield *args       end       return lambda{|*args| f.resume(*args) if f.alive? }     end   end end class fiberiterator   def initialize     @fiber_wrap=fiber.wrap         yield     end   end   def each     while value=@fiber_wrap.call       yield value     end   end end def perm(a)   fiberiterator.new{ permgen(a,a.size) } end def permgen (a, n)     if n == 0        fiber.yield     else         n.times |i|            a[n-1], a[i] = a[i], a[n-1]            permgen(a, n - 1)            a[n-1], a[i] = a[i], a[n-1]        end     end end def printresult (a)     p end  it=perm([1,2,3,4]) in   printresult(a) end 

the result include additional 3 after print out permutations have been printed. this?

the reason n.times returns n:

 1.times { } # => 1 

and return value permgen being caught , evaluated part of it , printed out. tired atm go through , understand what's yielded or resumed , when try , explain how it's getting caught , printed if permutation, can fix code changing permgen to:

def permgen (a, n)   if n == 0     fiber.yield   else     n.times |i|       a[n-1], a[i] = a[i], a[n-1]       permgen(a, n - 1)       a[n-1], a[i] = a[i], a[n-1]     end      nil # << added   end end 

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as side note, when ran code printing 4 not 3 @ end, based answer on being typo or result of different array or playing around different sized permutations.