Implement most of the spec reusing scribe & nefthera code

ocaml/lib/parsers/argument.ml

@@ -0,0 +1,23 @@
+let interpret (past: Schema.schema) (input: string list): Schema.schema =
+
+    let future = { past with output = { message = "" } } in
+
+    (* say is useful when the only change to future is the output message *)
+    let say (message: string) =
+        { future with output = { message = message } } in
+
+    (*
+       TODO: return a schema with orders, instead of calling side-effects
+       directly, making this more of a parser and less of a glorified switch
+    *)
+    match input with
+    | "pkg" :: tail -> System.Package.merge past tail
+    | "os" :: _ -> say (System.File.read "/etc/os-release")
+    | "host" :: _ -> say (System.Process.Reader.read [||] "hostname").output
+    | "echo" :: tail -> say (String.concat " " tail)
+    | ("version" | "-v" | "--version") :: _ ->
+        say (Schema.format_version future.meta.version)
+    | ("help" | "-h" | "--help") :: _ -> say future.meta.help.long
+    | head :: _ ->
+        say ("Unrecognized command: " ^ head ^ "\n" ^ future.meta.help.short)
+    | _ -> future