Handle break and return better.

examples/repl.rs

@@ -36,10 +36,18 @@ fn print_error(input: &str, err: EvalAltResult) {
             );
 
             println!("{}", lines[p.line().unwrap() - 1]);
+
+            let err_text = match err {
+                EvalAltResult::ErrorRuntime(err, _) if !err.is_empty() => {
+                    format!("Runtime error: {}", err)
+                }
+                _ => err.to_string(),
+            };
+
             println!(
                 "{}^ {}",
                 padding(" ", p.position().unwrap() - 1),
-                err.to_string().replace(&pos_text, "")
+                err_text.replace(&pos_text, "")
             );
         }
     }
@@ -86,7 +94,12 @@ fn main() {
             .map_err(EvalAltResult::ErrorParsing)
             .and_then(|r| {
                 ast = Some(r);
-                engine.consume_ast_with_scope(&mut scope, true, ast.as_ref().unwrap())
+                engine
+                    .consume_ast_with_scope(&mut scope, true, ast.as_ref().unwrap())
+                    .or_else(|err| match err {
+                        EvalAltResult::Return(_, _) => Ok(()),
+                        err => Err(err),
+                    })
             })
         {
             println!("");

examples/rhai_runner.rs

@@ -31,7 +31,13 @@ fn eprint_error(input: &str, err: EvalAltResult) {
             // EOF
             let line = lines.len() - 1;
             let pos = lines[line - 1].len();
-            eprint_line(&lines, line, pos, &err.to_string());
+            let err_text = match err {
+                EvalAltResult::ErrorRuntime(err, _) if !err.is_empty() => {
+                    format!("Runtime error: {}", err)
+                }
+                _ => err.to_string(),
+            };
+            eprint_line(&lines, line, pos, &err_text);
         }
         p if p.is_none() => {
             // No position

src/engine.rs

@@ -1068,7 +1068,9 @@ impl Engine<'_> {
                         if *guard_val {
                             match self.eval_stmt(scope, body) {
                                 Ok(_) => (),
-                                Err(EvalAltResult::LoopBreak) => return Ok(().into_dynamic()),
+                                Err(EvalAltResult::ErrorLoopBreak(_)) => {
+                                    return Ok(().into_dynamic())
+                                }
                                 Err(x) => return Err(x),
                             }
                         } else {
@@ -1083,7 +1085,7 @@ impl Engine<'_> {
             Stmt::Loop(body) => loop {
                 match self.eval_stmt(scope, body) {
                     Ok(_) => (),
-                    Err(EvalAltResult::LoopBreak) => return Ok(().into_dynamic()),
+                    Err(EvalAltResult::ErrorLoopBreak(_)) => return Ok(().into_dynamic()),
                     Err(x) => return Err(x),
                 }
             },
@@ -1102,7 +1104,7 @@ impl Engine<'_> {
 
                         match self.eval_stmt(scope, body) {
                             Ok(_) => (),
-                            Err(EvalAltResult::LoopBreak) => break,
+                            Err(EvalAltResult::ErrorLoopBreak(_)) => break,
                             Err(x) => return Err(x),
                         }
                     }
@@ -1114,7 +1116,7 @@ impl Engine<'_> {
             }
 
             // Break statement
-            Stmt::Break(_) => Err(EvalAltResult::LoopBreak),
+            Stmt::Break(pos) => Err(EvalAltResult::ErrorLoopBreak(*pos)),
 
             // Empty return
             Stmt::ReturnWithVal(None, ReturnType::Return, pos) => {

src/error.rs

@@ -82,12 +82,17 @@ pub enum ParseErrorType {
     /// A function definition is missing the parameters list. Wrapped value is the function name.
     #[cfg(not(feature = "no_function"))]
     FnMissingParams(String),
+    /// A function definition is missing the body. Wrapped value is the function name.
+    #[cfg(not(feature = "no_function"))]
+    FnMissingBody(String),
     /// Assignment to an inappropriate LHS (left-hand-side) expression.
     AssignmentToInvalidLHS,
     /// Assignment to a copy of a value.
     AssignmentToCopy,
     /// Assignment to an a constant variable.
     AssignmentToConstant(String),
+    /// Break statement not inside a loop.
+    LoopBreak,
 }
 
 /// Error when parsing a script.
@@ -133,10 +138,13 @@ impl ParseError {
             #[cfg(not(feature = "no_function"))]
             ParseErrorType::FnMissingParams(_) => "Expecting parameters in function declaration",
             #[cfg(not(feature = "no_function"))]
+            ParseErrorType::FnMissingBody(_) => "Expecting body statement block for function declaration",
+            #[cfg(not(feature = "no_function"))]
             ParseErrorType::WrongFnDefinition => "Function definitions must be at global level and cannot be inside a block or another function",
             ParseErrorType::AssignmentToInvalidLHS => "Cannot assign to this expression",
             ParseErrorType::AssignmentToCopy => "Cannot assign to this expression because it will only be changing a copy of the value",
-            ParseErrorType::AssignmentToConstant(_) => "Cannot assign to a constant variable."
+            ParseErrorType::AssignmentToConstant(_) => "Cannot assign to a constant variable.",
+            ParseErrorType::LoopBreak => "Break statement should only be used inside a loop"
         }
     }
 }
@@ -164,6 +172,11 @@ impl fmt::Display for ParseError {
                 write!(f, "Expecting parameters for function '{}'", s)?
             }
 
+            #[cfg(not(feature = "no_function"))]
+            ParseErrorType::FnMissingBody(ref s) => {
+                write!(f, "Expecting body statement block for function '{}'", s)?
+            }
+
             ParseErrorType::MissingRightParen(ref s) | ParseErrorType::MissingRightBrace(ref s) => {
                 write!(f, "{} for {}", self.desc(), s)?
             }

src/optimize.rs

@@ -4,7 +4,7 @@ use crate::any::{Any, Dynamic};
 use crate::engine::{
     Engine, FnCallArgs, KEYWORD_DEBUG, KEYWORD_DUMP_AST, KEYWORD_PRINT, KEYWORD_TYPE_OF,
 };
-use crate::parser::{map_dynamic_to_expr, Expr, FnDef, Stmt, AST};
+use crate::parser::{map_dynamic_to_expr, Expr, FnDef, ReturnType, Stmt, AST};
 use crate::scope::{Scope, ScopeEntry, VariableType};
 
 use crate::stdlib::{
@@ -121,18 +121,40 @@ fn optimize_stmt<'a>(stmt: Stmt, state: &mut State<'a>, preserve_result: bool) -
                 Stmt::Noop(pos)
             }
             Expr::True(_) => Stmt::Loop(Box::new(optimize_stmt(*stmt, state, false))),
-            expr => Stmt::While(
+            expr => match optimize_stmt(*stmt, state, false) {
-                Box::new(optimize_expr(expr, state)),
+                Stmt::Break(pos) => {
-                Box::new(optimize_stmt(*stmt, state, false)),
+                    // Only a single break statement - turn into running the guard expression once
-            ),
+                    state.set_dirty();
+                    let mut statements = vec![Stmt::Expr(Box::new(optimize_expr(expr, state)))];
+                    if preserve_result {
+                        statements.push(Stmt::Noop(pos))
+                    }
+                    Stmt::Block(statements, pos)
+                }
+                stmt => Stmt::While(Box::new(optimize_expr(expr, state)), Box::new(stmt)),
+            },
+        },
+        Stmt::Loop(stmt) => match optimize_stmt(*stmt, state, false) {
+            Stmt::Break(pos) => {
+                // Only a single break statement
+                state.set_dirty();
+                Stmt::Noop(pos)
+            }
+            stmt => Stmt::Loop(Box::new(stmt)),
         },
-
-        Stmt::Loop(stmt) => Stmt::Loop(Box::new(optimize_stmt(*stmt, state, false))),
         Stmt::For(id, expr, stmt) => Stmt::For(
             id,
             Box::new(optimize_expr(*expr, state)),
-            Box::new(optimize_stmt(*stmt, state, false)),
+            Box::new(match optimize_stmt(*stmt, state, false) {
+                Stmt::Break(pos) => {
+                    // Only a single break statement
+                    state.set_dirty();
+                    Stmt::Noop(pos)
+                }
+                stmt => stmt,
+            }),
         ),
+
         Stmt::Let(id, Some(expr), pos) => {
             Stmt::Let(id, Some(Box::new(optimize_expr(*expr, state))), pos)
         }
@@ -153,15 +175,12 @@ fn optimize_stmt<'a>(stmt: Stmt, state: &mut State<'a>, preserve_result: bool) -
                         optimize_stmt(stmt, state, preserve_result) // Optimize the statement
                     }
                 })
-                .enumerate()
-                .filter(|(i, stmt)| stmt.is_op() || (preserve_result && *i == orig_len - 1)) // Remove no-op's but leave the last one if we need the result
-                .map(|(_, stmt)| stmt)
                 .collect();
 
             // Remove all raw expression statements that are pure except for the very last statement
             let last_stmt = if preserve_result { result.pop() } else { None };
 
-            result.retain(|stmt| !matches!(stmt, Stmt::Expr(expr) if expr.is_pure()));
+            result.retain(|stmt| !stmt.is_pure());
 
             if let Some(stmt) = last_stmt {
                 result.push(stmt);
@@ -197,6 +216,24 @@ fn optimize_stmt<'a>(stmt: Stmt, state: &mut State<'a>, preserve_result: bool) -
                     .collect();
             }
 
+            // Remove everything following the the first return/throw
+            let mut dead_code = false;
+
+            result.retain(|stmt| {
+                if dead_code {
+                    return false;
+                }
+
+                match stmt {
+                    Stmt::ReturnWithVal(_, _, _) | Stmt::Break(_) => {
+                        dead_code = true;
+                    }
+                    _ => (),
+                }
+
+                true
+            });
+
             if orig_len != result.len() {
                 state.set_dirty();
             }
@@ -504,7 +541,15 @@ pub fn optimize_ast(
                     OptimizationLevel::Simple | OptimizationLevel::Full => {
                         let pos = fn_def.body.position();
                         let mut body = optimize(vec![fn_def.body], None, &Scope::new());
-                        fn_def.body = body.pop().unwrap_or_else(|| Stmt::Noop(pos));
+                        fn_def.body = match body.pop().unwrap_or_else(|| Stmt::Noop(pos)) {
+                            Stmt::ReturnWithVal(Some(val), ReturnType::Return, _) => {
+                                Stmt::Expr(val)
+                            }
+                            Stmt::ReturnWithVal(None, ReturnType::Return, pos) => {
+                                Stmt::Expr(Box::new(Expr::Unit(pos)))
+                            }
+                            stmt => stmt,
+                        };
                     }
                 }
                 Arc::new(fn_def)

src/parser.rs

@@ -201,6 +201,19 @@ pub enum Stmt {
 }
 
 impl Stmt {
+    pub fn position(&self) -> Position {
+        match self {
+            Stmt::Noop(pos)
+            | Stmt::Let(_, _, pos)
+            | Stmt::Const(_, _, pos)
+            | Stmt::Block(_, pos)
+            | Stmt::Break(pos)
+            | Stmt::ReturnWithVal(_, _, pos) => *pos,
+            Stmt::IfElse(expr, _, _) | Stmt::Expr(expr) => expr.position(),
+            Stmt::While(_, stmt) | Stmt::Loop(stmt) | Stmt::For(_, _, stmt) => stmt.position(),
+        }
+    }
+
     pub fn is_noop(&self) -> bool {
         matches!(self, Stmt::Noop(_))
     }
@@ -230,16 +243,21 @@ impl Stmt {
         }
     }
 
-    pub fn position(&self) -> Position {
+    pub fn is_pure(&self) -> bool {
         match self {
-            Stmt::Noop(pos)
+            Stmt::Noop(_) => true,
-            | Stmt::Let(_, _, pos)
+            Stmt::Expr(expr) => expr.is_pure(),
-            | Stmt::Const(_, _, pos)
+            Stmt::IfElse(guard, if_block, Some(else_block)) => {
-            | Stmt::Block(_, pos)
+                guard.is_pure() && if_block.is_pure() && else_block.is_pure()
-            | Stmt::Break(pos)
+            }
-            | Stmt::ReturnWithVal(_, _, pos) => *pos,
+            Stmt::IfElse(guard, block, None) | Stmt::While(guard, block) => {
-            Stmt::IfElse(expr, _, _) | Stmt::Expr(expr) => expr.position(),
+                guard.is_pure() && block.is_pure()
-            Stmt::While(_, stmt) | Stmt::Loop(stmt) | Stmt::For(_, _, stmt) => stmt.position(),
+            }
+            Stmt::Loop(block) => block.is_pure(),
+            Stmt::For(_, range, block) => range.is_pure() && block.is_pure(),
+            Stmt::Let(_, _, _) | Stmt::Const(_, _, _) => false,
+            Stmt::Block(statements, _) => statements.iter().all(Stmt::is_pure),
+            Stmt::Break(_) | Stmt::ReturnWithVal(_, _, _) => false,
         }
     }
 }
@@ -353,6 +371,8 @@ impl Expr {
 
             Expr::And(x, y) | Expr::Or(x, y) => x.is_pure() && y.is_pure(),
 
+            Expr::Stmt(stmt, _) => stmt.is_pure(),
+
             expr => expr.is_constant() || matches!(expr, Expr::Variable(_, _)),
         }
     }
@@ -1457,7 +1477,7 @@ fn parse_primary<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, Pa
     match input.peek() {
         Some((Token::LeftBrace, pos)) => {
             let pos = *pos;
-            return parse_block(input).map(|block| Expr::Stmt(Box::new(block), pos));
+            return parse_block(input, false).map(|block| Expr::Stmt(Box::new(block), pos));
         }
         _ => (),
     }
@@ -1467,8 +1487,9 @@ fn parse_primary<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, Pa
     let mut can_be_indexed = false;
 
     #[allow(unused_mut)]
-    let mut root_expr =
+    let mut root_expr = match token
-        match token.ok_or_else(|| ParseError::new(PERR::InputPastEndOfFile, Position::eof()))? {
+        .ok_or_else(|| ParseError::new(PERR::InputPastEndOfFile, Position::eof()))?
+    {
         #[cfg(not(feature = "no_float"))]
         (Token::FloatConstant(x), pos) => Ok(Expr::FloatConstant(x, pos)),
 
@@ -1493,7 +1514,7 @@ fn parse_primary<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, Pa
         }
         (Token::True, pos) => Ok(Expr::True(pos)),
         (Token::False, pos) => Ok(Expr::False(pos)),
-            (Token::LexError(le), pos) => Err(ParseError::new(PERR::BadInput(le.to_string()), pos)),
+        (Token::LexError(err), pos) => Err(ParseError::new(PERR::BadInput(err.to_string()), pos)),
         (token, pos) => Err(ParseError::new(
             PERR::BadInput(format!("Unexpected '{}'", token.syntax())),
             pos,
@@ -1814,19 +1835,22 @@ fn parse_expr<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, Parse
     parse_binary_op(input, 1, lhs)
 }
 
-fn parse_if<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {
+fn parse_if<'a>(
+    input: &mut Peekable<TokenIterator<'a>>,
+    breakable: bool,
+) -> Result<Stmt, ParseError> {
     input.next();
 
     let guard = parse_expr(input)?;
-    let if_body = parse_block(input)?;
+    let if_body = parse_block(input, breakable)?;
 
     let else_body = if matches!(input.peek(), Some((Token::Else, _))) {
         input.next();
 
         Some(Box::new(if matches!(input.peek(), Some((Token::If, _))) {
-            parse_if(input)?
+            parse_if(input, breakable)?
         } else {
-            parse_block(input)?
+            parse_block(input, breakable)?
         }))
     } else {
         None
@@ -1839,7 +1863,7 @@ fn parse_while<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Pars
     input.next();
 
     let guard = parse_expr(input)?;
-    let body = parse_block(input)?;
+    let body = parse_block(input, true)?;
 
     Ok(Stmt::While(Box::new(guard), Box::new(body)))
 }
@@ -1847,7 +1871,7 @@ fn parse_while<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Pars
 fn parse_loop<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {
     input.next();
 
-    let body = parse_block(input)?;
+    let body = parse_block(input, true)?;
 
     Ok(Stmt::Loop(Box::new(body)))
 }
@@ -1860,8 +1884,8 @@ fn parse_for<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseE
         .ok_or_else(|| ParseError::new(PERR::VariableExpected, Position::eof()))?
     {
         (Token::Identifier(s), _) => s,
-        (Token::LexError(s), pos) => {
+        (Token::LexError(err), pos) => {
-            return Err(ParseError::new(PERR::BadInput(s.to_string()), pos))
+            return Err(ParseError::new(PERR::BadInput(err.to_string()), pos))
         }
         (_, pos) => return Err(ParseError::new(PERR::VariableExpected, pos)),
     };
@@ -1875,7 +1899,7 @@ fn parse_for<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseE
     }
 
     let expr = parse_expr(input)?;
-    let body = parse_block(input)?;
+    let body = parse_block(input, true)?;
 
     Ok(Stmt::For(name, Box::new(expr), Box::new(body)))
 }
@@ -1894,8 +1918,8 @@ fn parse_var<'a>(
         .ok_or_else(|| ParseError::new(PERR::VariableExpected, Position::eof()))?
     {
         (Token::Identifier(s), _) => s,
-        (Token::LexError(s), pos) => {
+        (Token::LexError(err), pos) => {
-            return Err(ParseError::new(PERR::BadInput(s.to_string()), pos))
+            return Err(ParseError::new(PERR::BadInput(err.to_string()), pos))
         }
         (_, pos) => return Err(ParseError::new(PERR::VariableExpected, pos)),
     };
@@ -1921,7 +1945,10 @@ fn parse_var<'a>(
     }
 }
 
-fn parse_block<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {
+fn parse_block<'a>(
+    input: &mut Peekable<TokenIterator<'a>>,
+    breakable: bool,
+) -> Result<Stmt, ParseError> {
     let pos = match input
         .next()
         .ok_or_else(|| ParseError::new(PERR::MissingLeftBrace, Position::eof()))?
@@ -1932,30 +1959,20 @@ fn parse_block<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Pars
 
     let mut statements = Vec::new();
 
-    match input.peek().ok_or_else(|| {
+    while !matches!(input.peek(), Some((Token::RightBrace, _))) {
-        ParseError::new(
-            PERR::MissingRightBrace("end of block".into()),
-            Position::eof(),
-        )
-    })? {
-        (Token::RightBrace, _) => (), // empty block
-
-        _ => {
-            while input.peek().is_some() {
         // Parse statements inside the block
-                let stmt = parse_stmt(input)?;
+        let stmt = parse_stmt(input, breakable)?;
 
         // See if it needs a terminating semicolon
         let need_semicolon = !stmt.is_self_terminated();
 
         statements.push(stmt);
 
-                // End block with right brace
-                if let Some((Token::RightBrace, _)) = input.peek() {
-                    break;
-                }
-
         match input.peek() {
+            None => break,
+
+            Some((Token::RightBrace, _)) => break,
+
             Some((Token::SemiColon, _)) => {
                 input.next();
             }
@@ -1968,15 +1985,6 @@ fn parse_block<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Pars
                     *pos,
                 ));
             }
-
-                    None => {
-                        return Err(ParseError::new(
-                            PERR::MissingRightBrace("end of block".into()),
-                            Position::eof(),
-                        ))
-                    }
-                }
-            }
         }
     }
 
@@ -2001,7 +2009,10 @@ fn parse_expr_stmt<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt,
     Ok(Stmt::Expr(Box::new(parse_expr(input)?)))
 }
 
-fn parse_stmt<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {
+fn parse_stmt<'a>(
+    input: &mut Peekable<TokenIterator<'a>>,
+    breakable: bool,
+) -> Result<Stmt, ParseError> {
     match input
         .peek()
         .ok_or_else(|| ParseError::new(PERR::InputPastEndOfFile, Position::eof()))?
@@ -2009,15 +2020,16 @@ fn parse_stmt<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Parse
         #[cfg(not(feature = "no_function"))]
         (Token::Fn, pos) => return Err(ParseError::new(PERR::WrongFnDefinition, *pos)),
 
-        (Token::If, _) => parse_if(input),
+        (Token::If, _) => parse_if(input, breakable),
         (Token::While, _) => parse_while(input),
         (Token::Loop, _) => parse_loop(input),
         (Token::For, _) => parse_for(input),
-        (Token::Break, pos) => {
+        (Token::Break, pos) if breakable => {
             let pos = *pos;
             input.next();
             Ok(Stmt::Break(pos))
         }
+        (Token::Break, pos) => return Err(ParseError::new(PERR::LoopBreak, *pos)),
         (token @ Token::Return, _) | (token @ Token::Throw, _) => {
             let return_type = match token {
                 Token::Return => ReturnType::Return,
@@ -2038,12 +2050,15 @@ fn parse_stmt<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Parse
                 // return or throw with expression
                 Some((_, pos)) => {
                     let pos = *pos;
-                    let ret = parse_expr(input)?;
+                    Ok(Stmt::ReturnWithVal(
-                    Ok(Stmt::ReturnWithVal(Some(Box::new(ret)), return_type, pos))
+                        Some(Box::new(parse_expr(input)?)),
+                        return_type,
+                        pos,
+                    ))
                 }
             }
         }
-        (Token::LeftBrace, _) => parse_block(input),
+        (Token::LeftBrace, _) => parse_block(input, breakable),
         (Token::Let, _) => parse_var(input, VariableType::Normal),
         (Token::Const, _) => parse_var(input, VariableType::Constant),
         _ => parse_expr_stmt(input),
@@ -2137,7 +2152,11 @@ fn parse_fn<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<FnDef, ParseE
         }
     }
 
-    let body = parse_block(input)?;
+    let body = match input.peek() {
+        Some((Token::LeftBrace, _)) => parse_block(input, false)?,
+        Some((_, pos)) => return Err(ParseError::new(PERR::FnMissingBody(name), *pos)),
+        None => return Err(ParseError::new(PERR::FnMissingBody(name), Position::eof())),
+    };
 
     Ok(FnDef {
         name,
@@ -2169,7 +2188,7 @@ fn parse_global_level<'a, 'e>(
             }
         }
 
-        let stmt = parse_stmt(input)?;
+        let stmt = parse_stmt(input, false)?;
 
         let need_semicolon = !stmt.is_self_terminated();
 

src/result.rs

@@ -62,8 +62,8 @@ pub enum EvalAltResult {
     ErrorArithmetic(String, Position),
     /// Run-time error encountered. Wrapped value is the error message.
     ErrorRuntime(String, Position),
-    /// Internal use: Breaking out of loops.
+    /// Breaking out of loops - not an error if within a loop.
-    LoopBreak,
+    ErrorLoopBreak(Position),
     /// Not an error: Value returned from a script via the `return` keyword.
     /// Wrapped value is the result value.
     Return(Dynamic, Position),
@@ -106,7 +106,7 @@ impl EvalAltResult {
             Self::ErrorDotExpr(_, _) => "Malformed dot expression",
             Self::ErrorArithmetic(_, _) => "Arithmetic error",
             Self::ErrorRuntime(_, _) => "Runtime error",
-            Self::LoopBreak => "[Not Error] Breaks out of loop",
+            Self::ErrorLoopBreak(_) => "Break statement not inside a loop",
             Self::Return(_, _) => "[Not Error] Function returns value",
         }
     }
@@ -134,7 +134,7 @@ impl fmt::Display for EvalAltResult {
             Self::ErrorRuntime(s, pos) => {
                 write!(f, "{} ({})", if s.is_empty() { desc } else { s }, pos)
             }
-            Self::LoopBreak => write!(f, "{}", desc),
+            Self::ErrorLoopBreak(pos) => write!(f, "{} ({})", desc, pos),
             Self::Return(_, pos) => write!(f, "{} ({})", desc, pos),
             #[cfg(not(feature = "no_stdlib"))]
             Self::ErrorReadingScriptFile(path, err) => {
@@ -211,7 +211,6 @@ impl EvalAltResult {
         match self {
             #[cfg(not(feature = "no_stdlib"))]
             Self::ErrorReadingScriptFile(_, _) => Position::none(),
-            Self::LoopBreak => Position::none(),
 
             Self::ErrorParsing(err) => err.position(),
 
@@ -232,6 +231,7 @@ impl EvalAltResult {
             | Self::ErrorDotExpr(_, pos)
             | Self::ErrorArithmetic(_, pos)
             | Self::ErrorRuntime(_, pos)
+            | Self::ErrorLoopBreak(pos)
             | Self::Return(_, pos) => *pos,
         }
     }
@@ -240,7 +240,6 @@ impl EvalAltResult {
         match self {
             #[cfg(not(feature = "no_stdlib"))]
             Self::ErrorReadingScriptFile(_, _) => (),
-            Self::LoopBreak => (),
 
             Self::ErrorParsing(ParseError(_, ref mut pos))
             | Self::ErrorFunctionNotFound(_, ref mut pos)
@@ -260,6 +259,7 @@ impl EvalAltResult {
             | Self::ErrorDotExpr(_, ref mut pos)
             | Self::ErrorArithmetic(_, ref mut pos)
             | Self::ErrorRuntime(_, ref mut pos)
+            | Self::ErrorLoopBreak(ref mut pos)
             | Self::Return(_, ref mut pos) => *pos = new_position,
         }
     }

tests/looping.rs

@@ -1,10 +1,11 @@
-use rhai::{Engine, EvalAltResult};
+use rhai::{Engine, EvalAltResult, INT};
 
 #[test]
 fn test_loop() -> Result<(), EvalAltResult> {
     let mut engine = Engine::new();
 
-    assert!(engine.eval::<bool>(
+    assert_eq!(
+        engine.eval::<INT>(
             r"
 				let x = 0;
 				let i = 0;
@@ -13,15 +14,16 @@ fn test_loop() -> Result<(), EvalAltResult> {
 					if i < 10 {
 						x = x + i;
 						i = i + 1;
-				}
+					} else {
-				else {
 						break;
 					}
 				}
 
-			x == 45
+				return x;
 		"
-    )?);
+        )?,
+        45
+    );
 
     Ok(())
 }

tests/throw.rs

@@ -9,6 +9,6 @@ fn test_throw() {
         EvalAltResult::ErrorRuntime(s, _) if s == "hello"));
 
     assert!(matches!(
-        engine.eval::<()>(r#"throw;"#).expect_err("expects error"),
+        engine.eval::<()>(r#"throw"#).expect_err("expects error"),
         EvalAltResult::ErrorRuntime(s, _) if s == ""));
 }