Improve error reports; Add example

dust-lang/src/error.rs

@@ -46,7 +46,7 @@ impl Error {
 
                 (
                     Report::build(
-                        ReportKind::Custom("Parsing Error", Color::White),
+                        ReportKind::Custom("Parsing Error", Color::Yellow),
                         "input",
                         span.1,
                     )
@@ -73,7 +73,7 @@ impl Error {
 
                 (
                     Report::build(
-                        ReportKind::Custom("Lexing Error", Color::White),
+                        ReportKind::Custom("Lexing Error", Color::Yellow),
                         "input",
                         span.1,
                     )
@@ -89,9 +89,16 @@ impl Error {
             }
             Error::Runtime { error, position } => (
                 Report::build(
-                    ReportKind::Custom("Runtime Error", Color::White),
+                    ReportKind::Custom("Runtime Error", Color::Red),
                     "input",
                     position.1,
+                )
+                .with_message("An error occured that forced the program to exit.")
+                .with_note(
+                    "There may be unexpected side-effects because the program could not finish.",
+                )
+                .with_help(
+                    "This is the interpreter's fault. Please submit a bug with this error message.",
                 ),
                 if let RuntimeError::ValidationFailure(validation_error) = error {
                     Some(validation_error)
@@ -102,10 +109,11 @@ impl Error {
             ),
             Error::Validation { error, position } => (
                 Report::build(
-                    ReportKind::Custom("Validation Error", Color::White),
+                    ReportKind::Custom("Validation Error", Color::Magenta),
                     "input",
                     position.1,
                 )
+                .with_message("The syntax is valid but this code is not sound.")
                 .with_note("This error was detected by the interpreter before running the code."),
                 Some(error),
                 position,

examples/guessing_game.ds

@@ -0,0 +1,19 @@
+io.write_line("Guess the number.")
+
+secret_number = int.random_range(0..100)
+
+loop {
+	io.write_line("Input your guess.")
+
+	input = io.read_line() ? "Failed to read input."
+	guess = int.parse(input) ? "Failed to parse input."
+
+	if guess < secret_number {
+		io.write_line("Too low!")
+	} else if guess > secret_number {
+		io.write_line("Too high!")
+	} else {
+		io.write_line("You win!")
+		break
+	}
+}

examples/hello_world.ds

@@ -0,0 +1 @@
+io.write_line("Hello, world!")