pulling out a specific member of an array

[mr-c]

cwlVersion: v1.0
class: Workflow

inputs: []

steps: 
  generates_an_array:
     run: array_of_files.cwl
     in: {}
     out: [ an_array_of_files ]
  single_file_processor:
    run: only_one_file_input_tool.cwl
    in:
      raw_file:  # this is type: File
        source: generates_an_array/an_array_of_files
        valueFrom: $(self[0])
    out: [ result ]

outputs:
  result:
    type: File
    outputSource: single_file_processor/result