Merge pull request #41 from luciusmagn/master

Loops, comments, refactor, docs, unary operators

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "rhai"
-version = "0.5.1"
+version = "0.6.2"
 authors = ["Jonathan Turner", "Lukáš Hozda"]
 description = "Embedded scripting for Rust"
 homepage = "https://github.com/jonathandturner/rhai"

README.md

@@ -37,12 +37,36 @@ The repository contains several examples in the `examples` folder:
 - `reuse_scope` evaluates two pieces of code in separate runs, but using a common scope
 - `rhai_runner` runs each filename passed to it as a Rhai script
 - `simple_fn` shows how to register a Rust function to a Rhai engine
+- `repl` a simple REPL, see source code for what it can do at the moment
 
 Examples can be run with the following command:
 ```bash
 cargo run --example name
 ```
 
+## Example Scripts
+We also have a few examples scripts that showcase Rhai's features, all stored in the `scripts` folder:
+- `array.rhai` - arrays in Rhai
+- `assignment.rhai` - variable declarations
+- `comments.rhai` - just comments
+- `function_decl1.rhai` - a function without parameters
+- `function_decl2.rhai` - a function with two parameters
+- `function_decl3.rhai` - a function with many parameters
+- `if1.rhai` - if example
+- `loop.rhai` - endless loop in Rhai, this example emulates a do..while cycle
+- `op1.rhai` - just a simple addition
+- `op2.rhai` - simple addition and multiplication
+- `op3.rhai` - change evaluation order with parenthesis
+- `speed_test.rhai` - a simple program to measure the speed of Rhai's interpreter
+- `string.rhai`- string operations
+- `while.rhai` - while loop
+
+To run the scripts, you can either make your own tiny program, or make use of the `rhai_runner`
+example program:
+```bash
+cargo run --example rhai_runner scripts/any_script.rhai
+```
+
 # Hello world
 
 To get going with Rhai, you create an instance of the scripting engine and then run eval.
@@ -289,6 +313,17 @@ while x > 0 {
 }
 ```
 
+## Loop
+```rust
+let x = 10;
+
+loop {
+    print(x);
+    x = x - 1;
+	if x == 0 { break; }
+}
+```
+
 ## Functions
 
 Rhai supports defining functions in script:
@@ -336,3 +371,18 @@ let name = "Bob";
 let middle_initial = 'C';
 ```
 
+## Comments
+
+```rust
+let /* intruder comment */ name = "Bob";
+// This is a very important comment
+/* This comment spans
+   multiple lines, so it
+   only makes sense that
+   it is even more important */
+
+/* Fear not, Rhai satisfies all your nesting
+   needs with nested comments:
+   /*/*/*/*/**/*/*/*/*/
+*/
+```

TODO

@@ -1,11 +1,7 @@
 pre 1.0:
-	- loop
 	- binary ops
-	- unary minus and negation
-	- bool ops
 	- basic threads
 	- stdlib
-	- comments
 	- floats
 	- REPL (consume functions)
 1.0:

scripts/comments.rhai

@@ -0,0 +1,10 @@
+// I am a single line comment!
+
+let /* I am a spy in a variable declaration! */ x = 5;
+
+/* I am a simple
+   multiline comment */
+
+/* look /* at /* that, /* multiline */ comments */ can be */ nested */
+
+/* sorrounded by */ x // comments

scripts/loop.rhai

@@ -0,0 +1,8 @@
+let x = 10;
+
+// simulate do..while using loop
+loop {
+    print(x);
+    x = x - 1;
+	if x <= 0 { break; }
+}

src/engine.rs

@@ -7,7 +7,7 @@ use std::fmt;
 use parser::{lex, parse, Expr, Stmt, FnDef};
 use fn_register::FnRegister;
 
-use std::ops::{Add, Sub, Mul, Div};
+use std::ops::{Add, Sub, Mul, Div, Neg};
 use std::cmp::{Ord, Eq};
 
 #[derive(Debug)]
@@ -91,14 +91,44 @@ pub enum FnType {
     InternalFn(FnDef),
 }
 
+/// Rhai's engine type. This is what you use to run Rhai scripts
+///
+/// ```rust
+/// extern crate rhai;
+/// use rhai::Engine;
+/// 
+/// fn main() {
+///     let mut engine = Engine::new();
+/// 
+///     if let Ok(result) = engine.eval::<i64>("40 + 2") {
+///         println!("Answer: {}", result);  // prints 42
+///     }
+/// }
+/// ```
 pub struct Engine {
     pub fns: HashMap<String, Vec<FnType>>,
 }
 
+/// A type containing information about current scope.
+/// Useful for keeping state between `Engine` runs
+///
+/// ```rust
+/// use rhai::{Engine, Scope};
+/// 
+/// let mut engine = Engine::new();
+/// let mut my_scope = Scope::new();
+/// 
+/// assert!(engine.eval_with_scope::<()>(&mut my_scope, "let x = 5;").is_ok());
+/// assert_eq!(engine.eval_with_scope::<i64>(&mut my_scope, "x + 1").unwrap(), 6);
+/// ```
+///
+/// Between runs, `Engine` only remembers functions when not using own `Scope`.
 pub type Scope = Vec<(String, Box<Any>)>;
 
 impl Engine {
-    fn call_fn(&self,
+    /// Universal method for calling functions, that are either
+    /// registered with the `Engine` or written in Rhai
+    pub fn call_fn(&self,
                name: &str,
                arg1: Option<&mut Box<Any>>,
                arg2: Option<&mut Box<Any>>,
@@ -500,6 +530,8 @@ impl Engine {
         }
     }
 
+    /// Register a type for use with Engine. Keep in mind that
+    /// your type must implement Clone.
     pub fn register_type<T: Clone + Any>(&mut self) {
         fn clone_helper<T: Clone>(t: T) -> T {
             t.clone()
@@ -508,6 +540,7 @@ impl Engine {
         self.register_fn("clone", clone_helper as fn(T) -> T);
     }
 
+    /// Register a get function for a member of a registered type
     pub fn register_get<T: Clone + Any, U: Clone + Any, F>(&mut self, name: &str, get_fn: F)
         where F: 'static + Fn(&mut T) -> U
     {
@@ -516,6 +549,7 @@ impl Engine {
         self.register_fn(&get_name, get_fn);
     }
 
+    /// Register a set function for a member of a registered type
     pub fn register_set<T: Clone + Any, U: Clone + Any, F>(&mut self, name: &str, set_fn: F)
         where F: 'static + Fn(&mut T, U) -> ()
     {
@@ -524,6 +558,7 @@ impl Engine {
         self.register_fn(&set_name, set_fn);
     }
 
+    /// Shorthand for registering both getters and setters
     pub fn register_get_set<T: Clone + Any, U: Clone + Any, F, G>(&mut self,
                                                                   name: &str,
                                                                   get_fn: F,
@@ -1153,6 +1188,19 @@ impl Engine {
                     }
                 }
             }
+            Stmt::Loop(ref body) => {
+                loop {
+                    match self.eval_stmt(scope, body) {
+                        Err(EvalAltResult::LoopBreak) => {
+                            return Ok(Box::new(()));
+                        }
+                        Err(x) => {
+                            return Err(x);
+                        }
+                        _ => (),
+                    }
+                }
+            }
             Stmt::Break => Err(EvalAltResult::LoopBreak),
             Stmt::Return => Err(EvalAltResult::Return(Box::new(()))),
             Stmt::ReturnWithVal(ref a) => {
@@ -1174,6 +1222,7 @@ impl Engine {
         }
     }
 
+    /// Evaluate a file
     pub fn eval_file<T: Any + Clone>(&mut self, fname: &str) -> Result<T, EvalAltResult> {
         use std::fs::File;
         use std::io::prelude::*;
@@ -1191,12 +1240,14 @@ impl Engine {
         }
     }
 
+    /// Evaluate a string
     pub fn eval<T: Any + Clone>(&mut self, input: &str) -> Result<T, EvalAltResult> {
         let mut scope: Scope = Vec::new();
 
         self.eval_with_scope(&mut scope, input)
     }
 
+    /// Evaluate with own scope
     pub fn eval_with_scope<T: Any + Clone>(&mut self,
                                            scope: &mut Scope,
                                            input: &str)
@@ -1241,6 +1292,9 @@ impl Engine {
         }
     }
 
+    /// Evaluate a file, but only return errors, if there are any.
+    /// Useful for when you don't need the result, but still need
+    /// to keep track of possible errors
     pub fn consume_file(&mut self, fname: &str) -> Result<(), EvalAltResult> {
         use std::fs::File;
         use std::io::prelude::*;
@@ -1260,6 +1314,9 @@ impl Engine {
         }
     }
 
+    /// Evaluate a string, but only return errors, if there are any.
+    /// Useful for when you don't need the result, but still need
+    /// to keep track of possible errors
     pub fn consume(&mut self, input: &str) -> Result<(), EvalAltResult> {
         let mut scope: Scope = Scope::new();
 
@@ -1268,6 +1325,9 @@ impl Engine {
         res
     }
 
+    /// Evaluate a string with own scoppe, but only return errors, if there are any.
+    /// Useful for when you don't need the result, but still need
+    /// to keep track of possible errors
     pub fn consume_with_scope(&mut self, scope: &mut Scope, input: &str) -> Result<(), EvalAltResult> {
         let tokens = lex(input);
 
@@ -1298,6 +1358,8 @@ impl Engine {
         }
     }
 
+    /// Register the default library. That means, numberic types, char, bool
+    /// String, arithmetics and string concatenations.
     pub fn register_default_lib(engine: &mut Engine) {
         engine.register_type::<i32>();
         engine.register_type::<u32>();
@@ -1317,6 +1379,14 @@ impl Engine {
             )
         }
 
+        macro_rules! reg_un {
+            ($engine:expr, $x:expr, $op:expr, $( $y:ty ),*) => (
+                $(
+                    $engine.register_fn($x, ($op as fn(x: $y)->$y));
+                )*
+            )
+        }
+
         macro_rules! reg_cmp {
             ($engine:expr, $x:expr, $op:expr, $( $y:ty ),*) => (
                 $(
@@ -1329,6 +1399,7 @@ impl Engine {
         fn sub<T: Sub>(x: T, y: T) -> <T as Sub>::Output { x - y }
         fn mul<T: Mul>(x: T, y: T) -> <T as Mul>::Output { x * y }
         fn div<T: Div>(x: T, y: T) -> <T as Div>::Output { x / y }
+        fn neg<T: Neg>(x: T) -> <T as Neg>::Output { -x }
         fn lt<T: Ord>(x: T, y: T)  -> bool { x < y  }
         fn lte<T: Ord>(x: T, y: T) -> bool { x <= y }
         fn gt<T: Ord>(x: T, y: T)  -> bool { x > y  }
@@ -1337,6 +1408,7 @@ impl Engine {
         fn ne<T: Eq>(x: T, y: T)   -> bool { x != y }
         fn and(x: bool, y: bool)   -> bool { x && y }
         fn or(x: bool, y: bool)    -> bool { x || y }
+        fn not(x: bool)            -> bool { !x }
         fn concat(x: String, y: String) -> String { x + &y }
 
         reg_op!(engine, "+", add, i32, i64, u32, u64, f32, f64);
@@ -1354,6 +1426,9 @@ impl Engine {
         reg_op!(engine, "||", or, bool);
         reg_op!(engine, "&&", and, bool);
 
+        reg_un!(engine, "-", neg, i32, i64, f32, f64);
+        reg_un!(engine, "!", not, bool);
+
         engine.register_fn("+", concat);
 
         // engine.register_fn("[]", idx);
@@ -1362,6 +1437,7 @@ impl Engine {
         // (*ent).push(FnType::ExternalFn2(Box::new(idx)));
     }
 
+    /// Make a new engine
     pub fn new() -> Engine {
         let mut engine = Engine { fns: HashMap::new() };
 

src/lib.rs

@@ -1,4 +1,39 @@
-//! Rhai - embedded scripting for Rust
+//! # Rhai - embedded scripting for Rust
+//! Rhai is a tiny, simple and very fast embedded scripting language for Rust
+//! that gives you a safe and easy way to add scripting to your applications.
+//! It provides a familiar syntax based on JS and Rust and a simple Rust interface.
+//! Here is a quick example. First, the contents of `my_script.rhai`:
+//! 
+//! ```rust_todo_disable_testing_enable_highlighting
+//! fn factorial(x) {
+//!     if x == 1 { return 1; }
+//!	    x * factorial(x - 1)
+//! }
+//!
+//! compute_something(factorial(10))
+//! ```
+//! 
+//! And the Rust part:
+//! 
+//! ```rust
+//! use rhai::{FnRegister, Engine};
+//! 
+//! fn compute_something(x: i64) -> bool {
+//!	    (x % 40) == 0
+//! }
+//! 
+//! let mut engine = Engine::new();
+//! engine.register_fn("compute_something", compute_something);
+//! # // Very ugly hack incoming, TODO
+//! # use std::fs::{File, remove_file};
+//! # use std::io::Write;
+//! # let mut f = File::create("my_script.rhai").unwrap();
+//! # let _ = write!(f, "{}", "fn f(x) { if x == 1 { return 1; } x * f(x-1) } compute_something(f(10))");
+//! assert!(engine.eval_file::<bool>("my_script.rhai").unwrap());
+//! # let _ = remove_file("my_script.rhai");
+//! ```
+//!
+//! [Check out the README on github for more information!](https://github.com/jonathandturner/rhai)
 
 // lints required by Rhai
 #![allow(unknown_lints,
@@ -16,3 +51,4 @@ mod tests;
 
 pub use engine::{Engine, Scope};
 pub use fn_register::FnRegister;
+

src/parser.rs

@@ -4,12 +4,13 @@ use std::iter::Peekable;
 use std::str::Chars;
 use std::char;
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum LexError {
     UnexpectedChar,
     MalformedEscapeSequence,
     MalformedNumber,
     MalformedChar,
+    Nothing
 }
 
 impl Error for LexError {
@@ -19,12 +20,9 @@ impl Error for LexError {
             LexError::MalformedEscapeSequence => "Unexpected values in escape sequence",
             LexError::MalformedNumber => "Unexpected characters in number",
             LexError::MalformedChar => "Char constant not a single character",
+            LexError::Nothing => "This error is for internal use only"
         }
     }
-
-    fn cause(&self) -> Option<&Error> {
-        None
-    }
 }
 
 impl fmt::Display for LexError {
@@ -88,6 +86,7 @@ pub enum Stmt {
     If(Box<Expr>, Box<Stmt>),
     IfElse(Box<Expr>, Box<Stmt>, Box<Stmt>),
     While(Box<Expr>, Box<Stmt>),
+    Loop(Box<Stmt>),
     Var(String, Option<Box<Expr>>),
     Block(Vec<Stmt>),
     Expr(Box<Expr>),
@@ -111,7 +110,7 @@ pub enum Expr {
     False,
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum Token {
     IntConst(i64),
     Identifier(String),
@@ -124,7 +123,9 @@ pub enum Token {
     LSquare,
     RSquare,
     Plus,
+    UnaryPlus,
     Minus,
+    UnaryMinus,
     Multiply,
     Divide,
     Semicolon,
@@ -138,6 +139,7 @@ pub enum Token {
     If,
     Else,
     While,
+    Loop,
     LessThan,
     GreaterThan,
     Bang,
@@ -157,7 +159,93 @@ pub enum Token {
     LexErr(LexError),
 }
 
+impl Token {
+    // if another operator is after these, it's probably an unary operator
+    // not sure about fn's name
+    pub fn is_next_unary(&self) -> bool {
+        use self::Token::*;
+
+        match *self {
+            LCurly           | // (+expr) - is unary
+            // RCurly           | {expr} - expr not unary & is closing
+            LParen           | // {-expr} - is unary
+            // RParen           | (expr) - expr not unary & is closing
+            LSquare          | // [-expr] - is unary
+            // RSquare          | [expr] - expr not unary & is closing
+            Plus             |
+            UnaryPlus        |
+            Minus            |
+            UnaryMinus       |
+            Multiply         |
+            Divide           |
+            Colon            |
+            Comma            |
+            Period           |
+            Equals           |
+            LessThan         |
+            GreaterThan      |
+            Bang             |
+            LessThanEqual    |
+            GreaterThanEqual |
+            EqualTo          |
+            NotEqualTo       |
+            Pipe             |
+            Or               |
+            Ampersand        |
+            And              |
+            If               |
+            While            |
+            Return => true,
+            _ => false,
+        }
+    }
+
+    #[allow(dead_code)]
+    pub fn is_bin_op(&self) -> bool {
+        use self::Token::*;
+
+        match *self {
+            RCurly           |
+            RParen           |
+            RSquare          |
+            Plus             |
+            Minus            |
+            Multiply         |
+            Divide           |
+            Comma            |
+            // Period           | <- does period count?
+            Equals           |
+            LessThan         |
+            GreaterThan      |
+            LessThanEqual    |
+            GreaterThanEqual |
+            EqualTo          |
+            NotEqualTo       |
+            Pipe             |
+            Or               |
+            Ampersand        |
+            And => true,
+            _ => false,
+        }
+    }
+
+    #[allow(dead_code)]
+    pub fn is_un_op(&self) -> bool {
+        use self::Token::*;
+
+        match *self {
+            UnaryPlus        |
+            UnaryMinus       |
+            Equals           |
+            Bang             |
+            Return => true,
+            _ => false,
+        }
+    }
+}
+
 pub struct TokenIterator<'a> {
+    last: Token,
     char_stream: Peekable<Chars<'a>>,
 }
 
@@ -264,12 +352,8 @@ impl<'a> TokenIterator<'a> {
         let out: String = result.iter().cloned().collect();
         Ok(out)
     }
-}
 
-impl<'a> Iterator for TokenIterator<'a> {
+    fn inner_next(&mut self) -> Option<Token> {
-    type Item = Token;
-
-    fn next(&mut self) -> Option<Self::Item> {
         while let Some(c) = self.char_stream.next() {
             match c {
                 '0'...'9' => {
@@ -316,6 +400,7 @@ impl<'a> Iterator for TokenIterator<'a> {
                         "if" => return Some(Token::If),
                         "else" => return Some(Token::Else),
                         "while" => return Some(Token::While),
+                        "loop" => return Some(Token::Loop),
                         "break" => return Some(Token::Break),
                         "return" => return Some(Token::Return),
                         "fn" => return Some(Token::Fn),
@@ -358,7 +443,8 @@ impl<'a> Iterator for TokenIterator<'a> {
                             self.char_stream.next();
                             Some(Token::PlusEquals)
                         },
-                        _ => Some(Token::Plus)
+                        _ if self.last.is_next_unary() => Some(Token::UnaryPlus),
+                        _ => Some(Token::Plus),
                     }
                 },
                 '-' => {
@@ -367,11 +453,41 @@ impl<'a> Iterator for TokenIterator<'a> {
                             self.char_stream.next();
                             Some(Token::MinusEquals)
                         },
-                        _ => Some(Token::Minus)
+                        _ if self.last.is_next_unary() => Some(Token::UnaryMinus),
+                        _ => Some(Token::Minus),
                     }
                 },
                 '*' => return Some(Token::Multiply),
-                '/' => return Some(Token::Divide),
+                '/' => {
+                    match self.char_stream.peek() {
+                        Some(&'/') => {
+                            self.char_stream.next();
+                            while let Some(c) = self.char_stream.next() {
+                                if c == '\n' { break; }
+                            }
+                        }
+                        Some(&'*') => {
+                            let mut level = 1;
+                            self.char_stream.next();
+                            while let Some(c) = self.char_stream.next() {
+                                match c {
+                                    '/' => if let Some('*') = self.char_stream.next() {
+                                        level+=1;
+                                    }
+                                    '*' => if let Some('/') = self.char_stream.next() {
+                                        level-=1;
+                                    }
+                                    _ => (),
+                                }
+
+                                if level == 0 {
+                                    break;
+                                }
+                            }
+                        }
+                        _ => return Some(Token::Divide),
+                    }
+                }
                 ';' => return Some(Token::Semicolon),
                 ':' => return Some(Token::Colon),
                 ',' => return Some(Token::Comma),
@@ -439,8 +555,21 @@ impl<'a> Iterator for TokenIterator<'a> {
     }
 }
 
+impl<'a> Iterator for TokenIterator<'a> {
+    type Item = Token;
+
+    // TODO - perhaps this could be optimized?
+    fn next(&mut self) -> Option<Self::Item> {
+        self.last = match self.inner_next() {
+            Some(c) => c,
+            None => return None,
+        };
+        Some(self.last.clone())
+    }
+}
+
 pub fn lex(input: &str) -> TokenIterator {
-    TokenIterator { char_stream: input.chars().peekable() }
+    TokenIterator { last: Token::LexErr(LexError::Nothing), char_stream: input.chars().peekable() }
 }
 
 fn get_precedence(token: &Token) -> i32 {
@@ -590,6 +719,20 @@ fn parse_primary<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, Pa
     }
 }
 
+fn parse_unary<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, ParseError> {
+    let tok = match input.peek() {
+        Some(tok) => tok.clone(),
+        None => return Err(ParseError::InputPastEndOfFile),
+    };
+    
+    match tok {
+        Token::UnaryMinus => { input.next(); Ok(Expr::FnCall("-".to_string(), vec![parse_primary(input)?])) }
+        Token::UnaryPlus => { input.next(); parse_primary(input) }
+        Token::Bang => { input.next(); Ok(Expr::FnCall("!".to_string(), vec![parse_primary(input)?])) }
+        _ => parse_primary(input)
+    }
+}
+
 fn parse_binop<'a>(input: &mut Peekable<TokenIterator<'a>>,
                    prec: i32,
                    lhs: Expr)
@@ -608,7 +751,7 @@ fn parse_binop<'a>(input: &mut Peekable<TokenIterator<'a>>,
         }
 
         if let Some(op_token) = input.next() {
-            let mut rhs = try!(parse_primary(input));
+            let mut rhs = try!(parse_unary(input));
 
             let mut next_prec = -1;
 
@@ -663,7 +806,7 @@ fn parse_binop<'a>(input: &mut Peekable<TokenIterator<'a>>,
 }
 
 fn parse_expr<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Expr, ParseError> {
-    let lhs = try!(parse_primary(input));
+    let lhs = try!(parse_unary(input));
 
     parse_binop(input, 0, lhs)
 }
@@ -693,6 +836,14 @@ fn parse_while<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Pars
     Ok(Stmt::While(Box::new(guard), Box::new(body)))
 }
 
+fn parse_loop<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {
+    input.next();
+
+    let body = try!(parse_block(input));
+
+    Ok(Stmt::Loop(Box::new(body)))
+}
+
 fn parse_var<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, ParseError> {
     input.next();
 
@@ -756,6 +907,7 @@ fn parse_stmt<'a>(input: &mut Peekable<TokenIterator<'a>>) -> Result<Stmt, Parse
     match input.peek() {
         Some(&Token::If) => parse_if(input),
         Some(&Token::While) => parse_while(input),
+        Some(&Token::Loop) => parse_loop(input),
         Some(&Token::Break) => {
             input.next();
             Ok(Stmt::Break)

src/tests.rs

@@ -402,6 +402,62 @@ fn test_array_with_structs() {
     }
 }
 
+#[test]
+fn test_comments() {
+	let mut engine = Engine::new();
+
+	assert!(engine.eval::<i64>("let x = 5; x // I am a single line comment, yay!").is_ok());
+
+	assert!(engine.eval::<i64>("let /* I am a multiline comment, yay! */ x = 5; x").is_ok());
+}
+
+#[test]
+fn test_unary_minus() {
+	let mut engine = Engine::new();
+
+	assert_eq!(engine.eval::<i64>("let x = -5; x").unwrap(), -5);
+
+	assert_eq!(engine.eval::<i64>("fn n(x) { -x } n(5)").unwrap(), -5);
+
+	assert_eq!(engine.eval::<i64>("5 - -(-5)").unwrap(), 0);
+}
+
+#[test]
+fn test_not() {
+	let mut engine = Engine::new();
+
+	assert_eq!(engine.eval::<bool>("let not_true = !true; not_true").unwrap(), false);
+
+	assert_eq!(engine.eval::<bool>("fn not(x) { !x } not(false)").unwrap(), true);
+
+	// TODO - do we allow stacking unary operators directly? e.g '!!!!!!!true'
+	assert_eq!(engine.eval::<bool>("!(!(!(!(true))))").unwrap(), true)
+}
+
+#[test]
+fn test_loop() {
+	let mut engine = Engine::new();
+
+	assert!(
+		engine.eval::<bool>("
+			let x = 0;
+			let i = 0;
+
+			loop {
+				if i < 10 {
+					x = x + i;
+					i = i + 1;
+				}
+				else {
+					break;
+				}
+			}
+
+			x == 45
+		").unwrap()
+	)
+}
+
 #[test]
 fn test_increment() {
     let mut engine = Engine::new();