iterating over files with multiple ISAs about stupidedi HOT 3 CLOSED

# ....
machine, = parser.read(Stupidedi::Reader.build(edi_content))

# After parsing, state machine is positioned at the end of input (last segment), so let's rewind
isa = machine.first

# We can't use isa.iterate(:ISA) here because #iterate always starts searching
# _after_ the cursor position, and would skip the first ISA!
#
# Note: if there was a way to rewind to right before the first segment, iterate
# would work just fine here. Or alternatively, #iterate could be made to search
# right at the current segment. Unfortunately this might break legacy code!
while isa.defined?
  # Unwrap Either<StateMachine> to just a StateMachine. This is safe because we just checked isa.defined?
  isa = isa.fetch

  # Note: this returns an Either<Zipper<Segment>>
  # seg = isa.segment

  # We can use #iterate here because GS occurs somewhere after an ISA, rather than in the same location as the ISA.
  isa.iterate(:GS) do |gs|
    puts extract(gs, 6)
  end

  # Find the next ISA segment, returns Either<StateMachine>
  isa = isa.find(:ISA)
end

puts "no more ISAs found. quitting."
sleep 1