allow user to modify std path

example.ox

@@ -1,2 +1 @@
 print("examp");
-print(to_string(100));

src/lib.rs

@@ -1,3 +1,5 @@
+use crate::helpers::destructive_loop;
+
 pub mod tokenizer;
 pub mod parser;
 pub mod interpreter;
@@ -12,18 +14,35 @@ pub mod errors;
 pub mod helpers;
 
 pub struct Config {
-    pub source_file: String
+    pub source_file: String,
+    pub std_file: Option<String>
 }
 
 impl Config {
     pub fn new(args: &mut impl Iterator<Item = String>) -> Config {
         args.next();
 
-        let source_file = args.next()
-            .expect("source_file not specified");
+        let mut std_file = None;
+
+        loop {
+            match args.next() {
+                Some(arg) => {
+
+                    match &arg[..] {
+                        "--std" => {
+                            std_file = Some(args.next().expect("std file not specified"))
+                        },
+                        _ => {
+                            return Config {
+                                source_file: arg,
+                                std_file
+                            }
+                        }
+                    }
 
-        Config {
-            source_file
+                },
+                None => panic!("source file not specified")
+            }
         }
     }
 }

src/main.rs

@@ -34,7 +34,9 @@ fn main() -> ExitCode {
     let mut memory = Memory::new();
     BuiltinFn::populate_memory(&mut memory);
 
-    execute_file("std.ox", &mut sim_memory, &mut memory);
+    let std_file = config.std_file
+        .unwrap_or(String::from("std.ox"));
+    execute_file(&std_file[..], &mut sim_memory, &mut memory);
     execute_file(&config.source_file[..], &mut sim_memory, &mut memory);
 
     0.into()