aoc: refactor main() function

aoc/src/lib.rs

@@ -1,6 +1,32 @@
+use std::env;
+
 pub type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
 
 #[macro_export]
 macro_rules! err {
     ($($string:expr),+) => (Box::<dyn std::error::Error>::from(format!($($string),+)))
 }
+
+type DayFunc = fn() -> Result<()>;
+
+pub fn run(days: &[DayFunc]) -> Result<()> {
+    let mut args = env::args();
+    args.next();
+
+    match args.next() {
+        Some(arg) => {
+            let day: usize = arg.parse().expect("Please provide a day number");
+            days[day - 1]().unwrap_or_else(|e| eprintln!("error running day specified: {}", e));
+        }
+        None => {
+            for (i, day) in days.iter().enumerate() {
+                let i = i + 1;
+                println!("day{}: ", i);
+                day().unwrap_or_else(|e| eprintln!("error running day {}: {}", i, e));
+                println!();
+            }
+        }
+    }
+
+    Ok(())
+}