Add comma operator and display implementations

+ Add comma token
 + Add tuple operator
 + Add tuple value type
 + Implement display for `tree::Node` and all related types
 + Add support for right-to-left chaining of operators with same precedence

The priority of chaining of operators with the same precedence remains left-to-right.
Only if two consecutive operators with the same precedence are right-to-left, they will be ordered right-to-left.

Implements #4.

README.md

@@ -191,3 +191,4 @@ See [LICENSE](LICENSE) for details.
 ## Closing Notes
 
 If you have any ideas for features or see any problems in the code, architecture, interface, algorithmics or documentation, please open an issue on github.
+If there is already an issue describing what you want to say, please add a thumbs up or whatever emoji you think fits to the issue, so I know which ones I should prioritize.

src/error/mod.rs

@@ -3,7 +3,11 @@ use token::PartialToken;
 
 #[derive(Debug, PartialEq)]
 pub enum Error {
-    WrongArgumentAmount {
+    WrongOperatorArgumentAmount {
+        expected: usize,
+        actual: usize,
+    },
+    WrongFunctionArgumentAmount {
         expected: usize,
         actual: usize,
     },
@@ -50,8 +54,12 @@ pub enum Error {
 }
 
 impl Error {
-    pub fn wrong_argument_amount(actual: usize, expected: usize) -> Self {
-        Error::WrongArgumentAmount { actual, expected }
+    pub fn wrong_operator_argument_amount(actual: usize, expected: usize) -> Self {
+        Error::WrongOperatorArgumentAmount { actual, expected }
+    }
+
+    pub fn wrong_function_argument_amount(actual: usize, expected: usize) -> Self {
+        Error::WrongFunctionArgumentAmount { actual, expected }
     }
 
     pub fn expected_number(actual: Value) -> Self {
@@ -67,11 +75,19 @@ impl Error {
     }
 }
 
-pub fn expect_argument_amount(actual: usize, expected: usize) -> Result<(), Error> {
+pub fn expect_operator_argument_amount(actual: usize, expected: usize) -> Result<(), Error> {
     if actual == expected {
         Ok(())
     } else {
-        Err(Error::wrong_argument_amount(actual, expected))
+        Err(Error::wrong_operator_argument_amount(actual, expected))
+    }
+}
+
+pub fn expect_function_argument_amount(actual: usize, expected: usize) -> Result<(), Error> {
+    if actual == expected {
+        Ok(())
+    } else {
+        Err(Error::wrong_function_argument_amount(actual, expected))
     }
 }
 

src/function/mod.rs

@@ -18,7 +18,7 @@ impl Function {
     }
 
     pub fn call(&self, arguments: &[Value]) -> Result<Value, Error> {
-        error::expect_argument_amount(self.argument_amount, arguments.len())?;
+        error::expect_function_argument_amount(arguments.len(), self.argument_amount)?;
         (self.function)(arguments)
     }
 }

src/lib.rs

@@ -175,6 +175,8 @@
 //! See [LICENSE](LICENSE) for details.
 //!
 
+extern crate core;
+
 mod configuration;
 pub mod error;
 mod function;
@@ -210,7 +212,7 @@ pub fn build_operator_tree(string: &str) -> Result<Node, Error> {
 mod test {
     use crate::{eval, value::Value};
     use configuration::HashMapConfiguration;
-    use error::Error;
+    use error::{expect_number, Error};
     use eval_with_configuration;
     use Function;
 
@@ -377,6 +379,88 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_n_ary_functions() {
+        let mut configuration = HashMapConfiguration::new();
+        configuration.insert_function(
+            "sub2",
+            Function::new(
+                1,
+                Box::new(|arguments| {
+                    if let Value::Int(int) = arguments[0] {
+                        Ok(Value::Int(int - 2))
+                    } else if let Value::Float(float) = arguments[0] {
+                        Ok(Value::Float(float - 2.0))
+                    } else {
+                        Err(Error::expected_number(arguments[0].clone()))
+                    }
+                }),
+            ),
+        );
+        configuration.insert_function(
+            "avg",
+            Function::new(
+                2,
+                Box::new(|arguments| {
+                    expect_number(&arguments[0])?;
+                    expect_number(&arguments[1])?;
+
+                    if let (Value::Int(a), Value::Int(b)) = (&arguments[0], &arguments[1]) {
+                        Ok(Value::Int((a + b) / 2))
+                    } else {
+                        Ok(Value::Float(
+                            (arguments[0].as_float()? + arguments[1].as_float()?) / 2.0,
+                        ))
+                    }
+                }),
+            ),
+        );
+        configuration.insert_function(
+            "muladd",
+            Function::new(
+                3,
+                Box::new(|arguments| {
+                    expect_number(&arguments[0])?;
+                    expect_number(&arguments[1])?;
+                    expect_number(&arguments[2])?;
+
+                    if let (Value::Int(a), Value::Int(b), Value::Int(c)) =
+                        (&arguments[0], &arguments[1], &arguments[2])
+                    {
+                        Ok(Value::Int(a * b + c))
+                    } else {
+                        Ok(Value::Float(
+                            arguments[0].as_float()? * arguments[1].as_float()?
+                                + arguments[2].as_float()?,
+                        ))
+                    }
+                }),
+            ),
+        );
+        configuration.insert_variable("five".to_string(), Value::Int(5));
+
+        assert_eq!(
+            eval_with_configuration("avg(7, 5)", &configuration),
+            Ok(Value::Int(6))
+        );
+        assert_eq!(
+            eval_with_configuration("avg(sub2 5, 5)", &configuration),
+            Ok(Value::Int(4))
+        );
+        assert_eq!(
+            eval_with_configuration("sub2(avg(3, 6))", &configuration),
+            Ok(Value::Int(2))
+        );
+        assert_eq!(
+            eval_with_configuration("sub2 avg(3, 6)", &configuration),
+            Ok(Value::Int(2))
+        );
+        assert_eq!(
+            eval_with_configuration("muladd(3, 6, -4)", &configuration),
+            Ok(Value::Int(14))
+        );
+    }
+
     #[test]
     fn test_errors() {
         assert_eq!(
@@ -387,7 +471,10 @@ mod test {
             eval("1-true"),
             Err(Error::expected_number(Value::Boolean(true)))
         );
-        assert_eq!(eval("true-"), Err(Error::wrong_argument_amount(1, 2)));
+        assert_eq!(
+            eval("true-"),
+            Err(Error::wrong_operator_argument_amount(1, 2))
+        );
         assert_eq!(eval("!(()true)"), Err(Error::AppendedToLeafNode));
     }
 }

src/operator/display.rs

@@ -0,0 +1,122 @@
+use operator::*;
+use std::fmt::{Display, Error, Formatter};
+
+impl Display for RootNode {
+    fn fmt(&self, _f: &mut Formatter) -> Result<(), Error> {
+        Ok(())
+    }
+}
+
+impl Display for Add {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "+")
+    }
+}
+
+impl Display for Sub {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "-")
+    }
+}
+
+impl Display for Neg {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "-")
+    }
+}
+
+impl Display for Mul {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "*")
+    }
+}
+
+impl Display for Div {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "/")
+    }
+}
+
+impl Display for Mod {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "%")
+    }
+}
+
+impl Display for Eq {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "==")
+    }
+}
+
+impl Display for Neq {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "!=")
+    }
+}
+
+impl Display for Gt {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, ">")
+    }
+}
+
+impl Display for Lt {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "<")
+    }
+}
+
+impl Display for Geq {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, ">=")
+    }
+}
+
+impl Display for Leq {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "<=")
+    }
+}
+
+impl Display for And {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "&&")
+    }
+}
+
+impl Display for Or {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "||")
+    }
+}
+
+impl Display for Not {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "!")
+    }
+}
+
+impl Display for Tuple {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, ", ")
+    }
+}
+
+impl Display for Const {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "{}", self.value)
+    }
+}
+
+impl Display for VariableIdentifier {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "{}", self.identifier)
+    }
+}
+
+impl Display for FunctionIdentifier {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "{}", self.identifier)
+    }
+}

src/operator/mod.rs

@@ -1,12 +1,20 @@
 use crate::{configuration::Configuration, error::*, value::Value};
-use std::fmt::Debug;
+use std::fmt::{Debug, Display};
 
-pub trait Operator: Debug {
+mod display;
+
+pub trait Operator: Debug + Display {
     /// Returns the precedence of the operator.
     /// A high precedence means that the operator has priority to be deeper in the tree.
     // Make this a const fn once #57563 is resolved
     fn precedence(&self) -> i32;
 
+    /// Returns true if chains of operators with the same precedence as this one should be evaluated left-to-right,
+    /// and false if they should be evaluated right-to-left.
+    /// Left-to-right chaining has priority if operators with different order but same precedence are chained.
+    // Make this a const fn once #57563 is resolved
+    fn is_left_to_right(&self) -> bool;
+
     /// True if this operator is a leaf, meaning it accepts no arguments.
     // Make this a const fn once #57563 is resolved
     fn is_leaf(&self) -> bool {
@@ -56,6 +64,9 @@ pub struct Or;
 #[derive(Debug)]
 pub struct Not;
 
+#[derive(Debug)]
+pub struct Tuple;
+
 #[derive(Debug)]
 pub struct Const {
     value: Value,
@@ -94,12 +105,16 @@ impl Operator for RootNode {
         200
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         1
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 1)?;
+        expect_operator_argument_amount(arguments.len(), 1)?;
         Ok(arguments[0].clone())
     }
 }
@@ -109,12 +124,16 @@ impl Operator for Add {
         95
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -135,12 +154,16 @@ impl Operator for Sub {
         95
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -161,12 +184,16 @@ impl Operator for Neg {
         110
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         1
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 1)?;
+        expect_operator_argument_amount(arguments.len(), 1)?;
         expect_number(&arguments[0])?;
 
         if arguments[0].is_int() {
@@ -182,12 +209,16 @@ impl Operator for Mul {
         100
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -208,12 +239,16 @@ impl Operator for Div {
         100
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -234,12 +269,16 @@ impl Operator for Mod {
         100
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -260,12 +299,16 @@ impl Operator for Eq {
         80
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
 
         if arguments[0] == arguments[1] {
             Ok(Value::Boolean(true))
@@ -280,12 +323,16 @@ impl Operator for Neq {
         80
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
 
         if arguments[0] != arguments[1] {
             Ok(Value::Boolean(true))
@@ -300,12 +347,16 @@ impl Operator for Gt {
         80
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -330,12 +381,16 @@ impl Operator for Lt {
         80
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -360,12 +415,16 @@ impl Operator for Geq {
         80
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -390,12 +449,16 @@ impl Operator for Leq {
         80
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         expect_number(&arguments[0])?;
         expect_number(&arguments[1])?;
 
@@ -420,12 +483,16 @@ impl Operator for And {
         75
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         let a = expect_boolean(&arguments[0])?;
         let b = expect_boolean(&arguments[1])?;
 
@@ -442,12 +509,16 @@ impl Operator for Or {
         70
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         2
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 2)?;
+        expect_operator_argument_amount(arguments.len(), 2)?;
         let a = expect_boolean(&arguments[0])?;
         let b = expect_boolean(&arguments[1])?;
 
@@ -464,12 +535,16 @@ impl Operator for Not {
         110
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         1
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 1)?;
+        expect_operator_argument_amount(arguments.len(), 1)?;
         let a = expect_boolean(&arguments[0])?;
 
         if !a {
@@ -480,17 +555,58 @@ impl Operator for Not {
     }
 }
 
+impl Operator for Tuple {
+    fn precedence(&self) -> i32 {
+        40
+    }
+
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
+    fn argument_amount(&self) -> usize {
+        2
+    }
+
+    fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
+        if let Value::Tuple(tuple) = &arguments[0] {
+            let mut tuple = tuple.clone();
+            if let Value::Tuple(tuple2) = &arguments[1] {
+                tuple.extend(tuple2.iter().cloned());
+            } else {
+                tuple.push(arguments[1].clone());
+            }
+            Ok(Value::from(tuple))
+        } else {
+            if let Value::Tuple(tuple) = &arguments[1] {
+                let mut tuple = tuple.clone();
+                tuple.insert(0, arguments[0].clone());
+                Ok(Value::from(tuple))
+            } else {
+                Ok(Value::from(vec![
+                    arguments[0].clone(),
+                    arguments[1].clone(),
+                ]))
+            }
+        }
+    }
+}
+
 impl Operator for Const {
     fn precedence(&self) -> i32 {
         200
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         0
     }
 
     fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
-        expect_argument_amount(arguments.len(), 0)?;
+        expect_operator_argument_amount(arguments.len(), 0)?;
 
         Ok(self.value.clone())
     }
@@ -501,6 +617,10 @@ impl Operator for VariableIdentifier {
         200
     }
 
+    fn is_left_to_right(&self) -> bool {
+        true
+    }
+
     fn argument_amount(&self) -> usize {
         0
     }
@@ -519,13 +639,24 @@ impl Operator for FunctionIdentifier {
         190
     }
 
+    fn is_left_to_right(&self) -> bool {
+        false
+    }
+
     fn argument_amount(&self) -> usize {
         1
     }
 
     fn eval(&self, arguments: &[Value], configuration: &Configuration) -> Result<Value, Error> {
+        expect_operator_argument_amount(arguments.len(), 1)?;
+
+        let arguments = if let Value::Tuple(arguments) = &arguments[0] {
+            arguments
+        } else {
+            arguments
+        };
+
         if let Some(function) = configuration.get_function(&self.identifier) {
-            // Function::call checks for correct argument amount
             function.call(arguments)
         } else {
             Err(Error::FunctionIdentifierNotFound(self.identifier.clone()))

src/token/mod.rs

@@ -3,7 +3,6 @@ use value::{FloatType, IntType};
 
 #[derive(Clone, PartialEq, Debug)]
 pub enum Token {
-    // Single character tokens
     // Arithmetic
     Plus,
     Minus,
@@ -26,7 +25,10 @@ pub enum Token {
     LBrace,
     RBrace,
 
-    // Complex tokens
+    // Aggregation
+    Comma,
+
+    // Values, Variables and Functions
     Identifier(String),
     Float(FloatType),
     Int(IntType),
@@ -65,6 +67,8 @@ fn char_to_partial_token(c: char) -> PartialToken {
         '(' => PartialToken::Token(Token::LBrace),
         ')' => PartialToken::Token(Token::RBrace),
 
+        ',' => PartialToken::Token(Token::Comma),
+
         c => {
             if c.is_whitespace() {
                 PartialToken::Whitespace
@@ -98,6 +102,8 @@ impl Token {
             Token::LBrace => true,
             Token::RBrace => false,
 
+            Token::Comma => false,
+
             Token::Identifier(_) => true,
             Token::Float(_) => true,
             Token::Int(_) => true,
@@ -127,6 +133,8 @@ impl Token {
             Token::LBrace => false,
             Token::RBrace => true,
 
+            Token::Comma => false,
+
             Token::Identifier(_) => true,
             Token::Float(_) => true,
             Token::Int(_) => true,

src/tree/display.rs

@@ -0,0 +1,12 @@
+use std::fmt::{Display, Error, Formatter};
+use Node;
+
+impl Display for Node {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        self.operator.fmt(f)?;
+        for child in self.children() {
+            write!(f, " {}", child)?;
+        }
+        Ok(())
+    }
+}

src/tree/mod.rs

@@ -1,6 +1,8 @@
 use crate::{configuration::Configuration, error::Error, operator::*, value::Value};
 use token::Token;
 
+mod display;
+
 #[derive(Debug)]
 pub struct Node {
     children: Vec<Node>,
@@ -40,14 +42,18 @@ impl Node {
     }
 
     fn insert_back_prioritized(&mut self, node: Node, is_root_node: bool) -> Result<(), Error> {
-        if self.operator().precedence() < node.operator().precedence() || is_root_node {
+        if self.operator().precedence() < node.operator().precedence() || is_root_node
+            // Right-to-left chaining
+            || (self.operator().precedence() == node.operator().precedence() && !self.operator().is_left_to_right() && !node.operator().is_left_to_right())
+        {
             if self.operator().is_leaf() {
                 Err(Error::AppendedToLeafNode)
             } else if self.has_correct_amount_of_children() {
                 if self.children.last().unwrap().operator().precedence()
                     < node.operator().precedence()
-                // Function call
-                //|| self.children().last().unwrap()
+                    // Right-to-left chaining
+                    || (self.children.last().unwrap().operator().precedence()
+                    == node.operator().precedence() && !self.children.last().unwrap().operator().is_left_to_right() && !node.operator().is_left_to_right())
                 {
                     self.children
                         .last_mut()
@@ -118,6 +124,8 @@ pub fn tokens_to_operator_tree(tokens: Vec<Token>) -> Result<Node, Error> {
                 }
             }
 
+            Token::Comma => Some(Node::new(Tuple)),
+
             Token::Identifier(identifier) => {
                 let mut result = Some(Node::new(VariableIdentifier::new(identifier.clone())));
                 if let Some(next) = next {

src/value/display.rs

@@ -0,0 +1,26 @@
+use std::fmt::{Display, Error, Formatter};
+use Value;
+
+impl Display for Value {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        match self {
+            Value::String(string) => write!(f, "\"{}\"", string),
+            Value::Float(float) => write!(f, "{}", float),
+            Value::Int(int) => write!(f, "{}", int),
+            Value::Boolean(boolean) => write!(f, "{}", boolean),
+            Value::Tuple(tuple) => {
+                write!(f, "(")?;
+                let mut once = false;
+                for value in tuple {
+                    if once {
+                        write!(f, ", ")?;
+                    } else {
+                        once = true;
+                    }
+                    value.fmt(f)?;
+                }
+                write!(f, ")")
+            }
+        }
+    }
+}

src/value/mod.rs

@@ -1,5 +1,7 @@
 use error::Error;
 
+mod display;
+
 pub type IntType = i64;
 pub type FloatType = f64;
 
@@ -9,6 +11,7 @@ pub enum Value {
     Float(FloatType),
     Int(IntType),
     Boolean(bool),
+    Tuple(Vec<Value>),
 }
 
 impl Value {
@@ -72,6 +75,12 @@ impl From<bool> for Value {
     }
 }
 
+impl From<Vec<Value>> for Value {
+    fn from(tuple: Vec<Value>) -> Self {
+        Value::Tuple(tuple)
+    }
+}
+
 impl From<Value> for Result<Value, Error> {
     fn from(value: Value) -> Self {
         Ok(value)