#' Retrieve Unique Speakers from Interview Transcript
#'
#' This function identifies and returns a vector of unique speaker 
#' identifiers present in an interview transcript. It first structures
#' the transcript using `structure_interview` to extract speaker names.
#'
#' @param interview A character vector representing the interview 
#'   transcript (as returned by `read_interview`). The lines should
#'   be tagged with speaker names within square brackets 
#'   (e.g., "\[Speaker1\] This is a line").
#'
#' @return A character vector containing the unique speaker identifiers
#'   found in the interview transcript.
#'
#' @examples
#' # Example usage:
#' speakers = retrieve_speaker(intrw)
#' 
#' @family process interview
#'
#' @export

retrieve_speaker = function(interview){
    structure = structure_interview(interview)
    speaker = unique(structure[["values"]])
    return(speaker)
}