NextFlow results per item in set

per_item.nf

#!/usr/bin/env nextflow

//the problem is 1, then the channel gets file(*) => UnixPath; > 1, then channel gets ArrayList<UnixPath>

starts=Channel.from(1,2,3,4)

process first {
  input:
    val start from starts
  output:
    set val(start), file("result.*.txt") into (firstOutA,firstOutB)

  shell:
   '''
     for i in {1..!{start}}
     do
        echo !{start} > result.${i}.txt
     done
   '''
}

perStart = firstOutB.flatMap{ f ->
   s = f[0]
   files = f[1]
   if(files instanceof List){
      files.collect{ r ->
        tuple(s, r)
      }
   }else{
        tuple(s, files)
   }
}

process eachA {
   input:
    set val(start), file(result) from firstOutA
   output:
    stdout resultA

   """
      echo $result $start
   """
}


process eachB {
   input:
    set val(start), file(result) from perStart
   output:
    stdout resultB

   """
      echo $result $start
   """
}

resultA.subscribe {
   println "A:"+it
}

resultB.subscribe{
  println "B:"+it
}