OCaml: Implement configuration parser, bind lexer tokens with schema

ocaml/lib/system/process/command.ml

@@ -1,8 +1,11 @@
 open Utilities.Aliases
 
+type schema = Schema.schema
+
 type status = Exit of int | Unevaluated
 type command = { name : string; arguments : string list; status : status }
 
+
 let format (command : command) : string =
     command.name ^ " with arguments: "
     ^ String.concat " " command.arguments
@@ -14,3 +17,22 @@ let format (command : command) : string =
 
 let format_many (commands : command list) : string list =
     List.map format commands
+
+let check_su_command (schema: schema): schema =
+    let command = schema.input.configuration.main.su_command in
+    let path = Reader.read [||] ("which " ^ command) in
+    try Unix.access path.output [Unix.X_OK]; schema
+    with Unix.Unix_error _ -> elog "";
+        {
+            schema with
+            output =
+                {
+                    schema.output with
+                    main =
+                        "Super user command " ^ command ^
+                        " not executable at path '" ^ path.output ^
+                        "' (exit status " ^ path.status ^ ", stderr: '" ^
+                        path.error ^ "')\n"
+                };
+            meta = { schema.meta with status = 1 };
+        }