main.nf

#!/usr/bin/env nextflow
nextflow.enable.dsl=2
nextflow.preview.recursion=true

params.input = 'data/*.dat'

process ScannerLightly {
    input:
    path datfile_accumulator
    val meta_accumulator

    output:
    path "add_me_to_list.*.txt", emit: txts
    val new_sampleid,            emit: ids

    script:
    println "datfile_accumulator: ${datfile_accumulator}"
    println "meta_accumulator: ${meta_accumulator}"
    new_sampleid = meta_accumulator.first()
    "echo adding $new_sampleid > add_me_to_list.${new_sampleid}.txt"
}

workflow {
    Channel.fromPath(params.input)
    | toSortedList
    | flatten
    | multiMap {
        datfiles: it
        sampleid: it.simpleName
    }
    | set { two_input_channels }

    ScannerLightly.scan(two_input_channels)

    ScannerLightly.out.txts | view
}