Simple Argument Parsing🔗

For many tools, you just need to check for specific flags or a single input file. Pattern matching on the list of strings is the most idiomatic way to do this.

def parseArgs (args : List String) : IO Unit := do
  match args with
  | [] | ["--help"] | ["-h"] =>
    IO.println "Usage: mytool [OPTIONS] [FILE]\n"
    IO.println "Options:"
    IO.println "  -h, --help     Show this help"
    IO.println "  -v, --version  Show version"

  | ["--version"] | ["-v"] =>
    IO.println "mytool version 1.0.0"
  | [filename] =>
    IO.println s!"Processing file: {filename}"
  | _ =>
    IO.eprintln "Error: Unknown or too many arguments.
      Use --help for usage."
    IO.Process.exit 1