try subcommand

src/main.rs

@@ -8,7 +8,7 @@ use std::{
 };
 use term::{clear_terminal, press_enter_prompt};
 
-use self::{app_state::AppState, dev::DevCommands, info_file::InfoFile};
+use self::{app_state::AppState, dev::DevCommands, info_file::InfoFile, url_replacer::UrlReplacer};
 
 mod app_state;
 mod cargo_toml;
@@ -22,6 +22,7 @@ mod list;
 mod run;
 mod term;
 mod watch;
+mod url_replacer;
 
 const CURRENT_FORMAT_VERSION: u8 = 1;
 
@@ -100,6 +101,8 @@ fn main() -> Result<ExitCode> {
         info_file.final_message.unwrap_or_default(),
     )?;
 
+    let replacer = UrlReplacer::new(&args.base_url);
+
     // Show the welcome message if the state file doesn't exist yet.
     if let Some(welcome_message) = info_file.welcome_message {
         match state_file_status {
@@ -184,7 +187,9 @@ fn main() -> Result<ExitCode> {
             if let Some(name) = name {
                 app_state.set_current_exercise_by_name(&name)?;
             }
-            println!("{}", app_state.current_exercise().hint);
+            
+            let hint = app_state.current_exercise().hint;
+            println!("{}", replacer.replace(hint));
         }
         // Handled in an earlier match.
         Some(Subcommands::Init | Subcommands::Dev(_)) => (),

src/url_replacer.rs

@@ -0,0 +1,21 @@
+pub struct UrlReplacer <'a> {
+    base_url: &'a Option<String>
+}
+
+const EN_BASE_URL: &str = "https://doc.rust-lang.org/book";
+
+impl <'a> UrlReplacer <'a> {
+    pub fn new(base_url: &'a Option<String>) -> Self {
+        Self {
+            base_url
+        }
+    }
+
+    pub fn replace(&self, hint: &str) -> String {
+        if let Some(base_url) = self.base_url {
+            hint.replace(EN_BASE_URL, base_url)
+        } else {
+            hint.to_owned()
+        }
+    }
+}