User-reported unhelpful error message

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Program: https://code.world/#PfRG9UTpw2IVmjnVtUdD2LQ

Message:

List index is too large.
When evaluating:
  error, called  in the standard library
  idxErrorTooLarge, called  in the standard library
  #, used at program.hs:103:65 in your code