Run a REPL if no arguments are given

README.md

@@ -16,7 +16,7 @@ together if the units are compatible:
     metrify 1 acre 15 square feet
 
 You can also invoke metrify without arguments, in which case it will give you a
-prompt to type the expression into.
+prompt to type the expression into. Press ^D to exit.
 
 Result display
 --------------

src/main.rs

@@ -9,31 +9,43 @@ fn main() {
 	let name = args[0].clone();
 	let args = args[1..].join(" ");
 
-	let mut input = args;
 
-	if input.len() == 0 {
-		print!("> ");
-		match io::stdout().flush() {
-			Ok(_) => {}
+	if args.len() == 0 {
+		loop {
+			print!("> ");
+			match io::stdout().flush() {
+				Ok(_) => {}
+				Err(err) => {
+					eprintln!("{name}: Error: {err}");
+					process::exit(1);
+				}
+			}
+			let mut input = String::new();
+			match io::stdin().read_line(&mut input) {
+				Ok(_) => {}
+				Err(err) => {
+					eprintln!("{name}: Error: {err}");
+					process::exit(1);
+				}
+			}
+			if input.len() == 0 {
+				println!(); // Add a newline if user pressed ^D
+				break;
+			}
+			match run(&input) {
+				Ok(str) => println!("{str}"),
+				Err(err) => {
+					eprintln!("Error: {err}");
+				}
+			}
+		}
+	} else {
+		match run(&args) {
+			Ok(str) => println!("{str}"),
 			Err(err) => {
 				eprintln!("{name}: Error: {err}");
 				process::exit(1);
 			}
 		}
-		match io::stdin().read_line(&mut input) {
-			Ok(_) => {}
-			Err(err) => {
-				eprintln!("{name}: Error: {err}");
-				process::exit(1);
-			}
-		}
-	}
-
-	match run(&input) {
-		Ok(str) => println!("{str}"),
-		Err(err) => {
-			eprintln!("{name}: Error: {err}");
-			process::exit(1);
-		}
 	}
 }