Extend VM, abstract tree and parser

dust-lang/src/analyzer.rs

@@ -12,11 +12,12 @@ use std::{
 use crate::{
     ast::{
         AbstractSyntaxTree, BlockExpression, CallExpression, ElseExpression, FieldAccessExpression,
-        IfExpression, LetStatement, ListExpression, ListIndexExpression, LoopExpression, Node,
+        IfExpression, LetStatement, ListExpression, ListIndexExpression, LoopExpression,
-        OperatorExpression, RangeExpression, Span, Statement, StructExpression,
+        MapExpression, Node, OperatorExpression, RangeExpression, Span, Statement,
-        TupleAccessExpression,
+        StructDefinition, StructExpression, TupleAccessExpression,
     },
-    parse, Context, DustError, Expression, Identifier, Type,
+    parse, Context, DustError, Expression, FieldsStructType, Identifier, StructType, TupleType,
+    Type,
 };
 
 /// Analyzes the abstract syntax tree for errors.
@@ -129,7 +130,37 @@ impl<'a> Analyzer<'a> {
                     value,
                 } => todo!(),
             },
-            Statement::StructDefinition(_) => {}
+            Statement::StructDefinition(struct_definition) => {
+                let (name, struct_type) = match &struct_definition.inner {
+                    StructDefinition::Unit { name } => {
+                        (name.inner.clone(), Type::Struct(StructType::Unit))
+                    }
+                    StructDefinition::Tuple { name, items } => {
+                        let fields = items.iter().map(|item| item.inner.clone()).collect();
+
+                        (
+                            name.inner.clone(),
+                            Type::Struct(StructType::Tuple(TupleType { fields })),
+                        )
+                    }
+                    StructDefinition::Fields { name, fields } => {
+                        let fields = fields
+                            .iter()
+                            .map(|(identifier, r#type)| {
+                                (identifier.inner.clone(), r#type.inner.clone())
+                            })
+                            .collect();
+
+                        (
+                            name.inner.clone(),
+                            Type::Struct(StructType::Fields(FieldsStructType { fields })),
+                        )
+                    }
+                };
+
+                self.context
+                    .set_type(name, struct_type, struct_definition.position);
+            }
         }
 
         Ok(())
@@ -204,6 +235,13 @@ impl<'a> Analyzer<'a> {
                     self.analyze_block(&block.inner)?;
                 }
             },
+            Expression::Map(map_expression) => {
+                let MapExpression { pairs } = map_expression.inner.as_ref();
+
+                for (_, expression) in pairs {
+                    self.analyze_expression(expression)?;
+                }
+            }
             Expression::Operator(operator_expression) => match operator_expression.inner.as_ref() {
                 OperatorExpression::Assignment { assignee, value } => {
                     self.analyze_expression(assignee)?;

dust-lang/src/ast/expression.rs

@@ -6,7 +6,9 @@ use std::{
 
 use serde::{Deserialize, Serialize};
 
-use crate::{Context, FieldsStructType, FunctionType, Identifier, StructType, TupleType, Type};
+use crate::{
+    Context, FieldsStructType, FunctionType, Identifier, RangeableType, StructType, TupleType, Type,
+};
 
 use super::{Node, Span, Statement};
 
@@ -22,6 +24,7 @@ pub enum Expression {
     ListIndex(Node<Box<ListIndexExpression>>),
     Literal(Node<Box<LiteralExpression>>),
     Loop(Node<Box<LoopExpression>>),
+    Map(Node<Box<MapExpression>>),
     Operator(Node<Box<OperatorExpression>>),
     Range(Node<Box<RangeExpression>>),
     Struct(Node<Box<StructExpression>>),
@@ -29,6 +32,15 @@ pub enum Expression {
 }
 
 impl Expression {
+    pub fn map(pairs: Vec<(Node<Identifier>, Expression)>, position: Span) -> Self {
+        Self::Map(Node::new(
+            Box::new(MapExpression {
+                pairs: pairs.into_iter().collect(),
+            }),
+            position,
+        ))
+    }
+
     pub fn operator(operator_expression: OperatorExpression, position: Span) -> Self {
         Self::Operator(Node::new(Box::new(operator_expression), position))
     }
@@ -323,6 +335,19 @@ impl Expression {
                 LoopExpression::Infinite { .. } => None,
                 LoopExpression::While { block, .. } => block.inner.return_type(context),
             },
+            Expression::Map(map_expression) => {
+                let MapExpression { pairs } = map_expression.inner.as_ref();
+
+                let mut types = HashMap::with_capacity(pairs.len());
+
+                for (key, value) in pairs {
+                    let value_type = value.return_type(context)?;
+
+                    types.insert(key.inner.clone(), value_type);
+                }
+
+                Some(Type::Map { pairs: types })
+            }
             Expression::Operator(operator_expression) => match operator_expression.inner.as_ref() {
                 OperatorExpression::Assignment { .. } => None,
                 OperatorExpression::Comparison { .. } => Some(Type::Boolean),
@@ -333,7 +358,24 @@ impl Expression {
                 OperatorExpression::Math { left, .. } => left.return_type(context),
                 OperatorExpression::Logic { .. } => Some(Type::Boolean),
             },
-            Expression::Range(_) => Some(Type::Range),
+            Expression::Range(range_expression) => {
+                let start = match range_expression.inner.as_ref() {
+                    RangeExpression::Exclusive { start, .. } => start,
+                    RangeExpression::Inclusive { start, end } => start,
+                };
+                let start_type = start.return_type(context)?;
+                let rangeable_type = match start_type {
+                    Type::Byte => RangeableType::Byte,
+                    Type::Character => RangeableType::Character,
+                    Type::Float => RangeableType::Float,
+                    Type::Integer => RangeableType::Integer,
+                    _ => return None,
+                };
+
+                Some(Type::Range {
+                    r#type: rangeable_type,
+                })
+            }
             Expression::Struct(struct_expression) => match struct_expression.inner.as_ref() {
                 StructExpression::Fields { fields, .. } => {
                     let mut types = HashMap::with_capacity(fields.len());
@@ -375,6 +417,7 @@ impl Expression {
             Expression::ListIndex(list_index) => list_index.position,
             Expression::Literal(literal) => literal.position,
             Expression::Loop(r#loop) => r#loop.position,
+            Expression::Map(map) => map.position,
             Expression::Operator(operator) => operator.position,
             Expression::Range(range) => range.position,
             Expression::Struct(r#struct) => r#struct.position,
@@ -396,6 +439,7 @@ impl Display for Expression {
             Expression::ListIndex(list_index) => write!(f, "{}", list_index.inner),
             Expression::Literal(literal) => write!(f, "{}", literal.inner),
             Expression::Loop(r#loop) => write!(f, "{}", r#loop.inner),
+            Expression::Map(map) => write!(f, "{}", map.inner),
             Expression::Operator(operator) => write!(f, "{}", operator.inner),
             Expression::Range(range) => write!(f, "{}", range),
             Expression::Struct(r#struct) => write!(f, "{}", r#struct.inner),
@@ -404,6 +448,27 @@ impl Display for Expression {
     }
 }
 
+#[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
+pub struct MapExpression {
+    pub pairs: Vec<(Node<Identifier>, Expression)>,
+}
+
+impl Display for MapExpression {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{{")?;
+
+        for (index, (key, value)) in self.pairs.iter().enumerate() {
+            if index > 0 {
+                write!(f, ", ")?;
+            }
+
+            write!(f, "{} = {}", key.inner, value)?;
+        }
+
+        write!(f, "}}")
+    }
+}
+
 #[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
 pub struct TupleAccessExpression {
     pub tuple: Expression,

dust-lang/src/lexer.rs

@@ -433,6 +433,7 @@ impl<'src> Lexer<'src> {
             "is_odd" => Token::IsOdd,
             "length" => Token::Length,
             "let" => Token::Let,
+            "map" => Token::Map,
             "mut" => Token::Mut,
             "read_line" => Token::ReadLine,
             "struct" => Token::Struct,
@@ -501,6 +502,32 @@ impl Display for LexError {
 mod tests {
     use super::*;
 
+    #[test]
+    fn map_expression() {
+        let input = "map { x = '1', y = 2, z = 3.0 }";
+
+        assert_eq!(
+            lex(input),
+            Ok(vec![
+                (Token::Map, (0, 3)),
+                (Token::LeftCurlyBrace, (4, 5)),
+                (Token::Identifier("x"), (6, 7)),
+                (Token::Equal, (8, 9)),
+                (Token::String("1"), (10, 13)),
+                (Token::Comma, (13, 14)),
+                (Token::Identifier("y"), (15, 16)),
+                (Token::Equal, (17, 18)),
+                (Token::Integer("2"), (19, 20)),
+                (Token::Comma, (20, 21)),
+                (Token::Identifier("z"), (22, 23)),
+                (Token::Equal, (24, 25)),
+                (Token::Float("3.0"), (26, 29)),
+                (Token::RightCurlyBrace, (30, 31)),
+                (Token::Eof, (31, 31)),
+            ])
+        );
+    }
+
     #[test]
     fn let_statement() {
         let input = "let x = 42";

dust-lang/src/parser.rs

@@ -4,7 +4,6 @@
 //! - `parse` convenience function
 //! - `Parser` struct, which parses the input a statement at a time
 use std::{
-    collections::VecDeque,
     error::Error,
     fmt::{self, Display, Formatter},
     num::{ParseFloatError, ParseIntError},
@@ -180,10 +179,8 @@ impl<'src> Parser<'src> {
 
             self.next_token()?;
 
-            let (name, name_end) = if let Token::Identifier(_) = self.current_token {
+            let name = if let Token::Identifier(_) = self.current_token {
-                let end = self.current_position.1;
+                self.parse_identifier()?
-
-                (self.parse_identifier()?, end)
             } else {
                 return Err(ParseError::ExpectedToken {
                     expected: TokenKind::Identifier,
@@ -192,6 +189,17 @@ impl<'src> Parser<'src> {
                 });
             };
 
+            if let Token::Semicolon = self.current_token {
+                let end = self.current_position.1;
+
+                self.next_token()?;
+
+                return Ok(Statement::struct_definition(
+                    StructDefinition::Unit { name },
+                    (start_position.0, end),
+                ));
+            }
+
             if let Token::LeftParenthesis = self.current_token {
                 self.next_token()?;
 
@@ -199,26 +207,45 @@ impl<'src> Parser<'src> {
 
                 loop {
                     if let Token::RightParenthesis = self.current_token {
-                        let position = (start_position.0, self.current_position.1);
-
                         self.next_token()?;
 
-                        return Ok(Statement::struct_definition(
+                        if let Token::Semicolon = self.current_token {
-                            StructDefinition::Tuple { name, items: types },
+                            break;
-                            position,
+                        } else {
-                        ));
+                            return Err(ParseError::ExpectedToken {
+                                expected: TokenKind::Semicolon,
+                                actual: self.current_token.to_owned(),
+                                position: self.current_position,
+                            });
                         }
+                    }
+
+                    let type_node = self.parse_type()?;
+
+                    types.push(type_node);
 
                     if let Token::Comma = self.current_token {
                         self.next_token()?;
 
                         continue;
                     }
-
-                    let type_node = self.parse_type()?;
-
-                    types.push(type_node);
                 }
+
+                let position = (start_position.0, self.current_position.1);
+
+                self.next_token()?;
+
+                return if types.is_empty() {
+                    Ok(Statement::struct_definition(
+                        StructDefinition::Unit { name },
+                        position,
+                    ))
+                } else {
+                    Ok(Statement::struct_definition(
+                        StructDefinition::Tuple { name, items: types },
+                        position,
+                    ))
+                };
             }
 
             if let Token::LeftCurlyBrace = self.current_token {
@@ -228,20 +255,11 @@ impl<'src> Parser<'src> {
 
                 loop {
                     if let Token::RightCurlyBrace = self.current_token {
-                        let position = (start_position.0, self.current_position.1);
+                        if let Token::Semicolon = self.current_token {
-
                             self.next_token()?;
-
-                        return Ok(Statement::struct_definition(
-                            StructDefinition::Fields { name, fields },
-                            position,
-                        ));
                         }
 
-                    if let Token::Comma = self.current_token {
+                        break;
-                        self.next_token()?;
-
-                        continue;
                     }
 
                     let field_name = self.parse_identifier()?;
@@ -259,13 +277,40 @@ impl<'src> Parser<'src> {
                     let field_type = self.parse_type()?;
 
                     fields.push((field_name, field_type));
+
+                    if let Token::Comma = self.current_token {
+                        self.next_token()?;
+
+                        continue;
                     }
                 }
 
-            return Ok(Statement::struct_definition(
+                let position = (start_position.0, self.current_position.1);
+
+                self.next_token()?;
+
+                return if fields.is_empty() {
+                    Ok(Statement::struct_definition(
                         StructDefinition::Unit { name },
-                (start_position.0, name_end),
+                        position,
-            ));
+                    ))
+                } else {
+                    Ok(Statement::struct_definition(
+                        StructDefinition::Fields { name, fields },
+                        position,
+                    ))
+                };
+            }
+
+            return Err(ParseError::ExpectedTokenMultiple {
+                expected: vec![
+                    TokenKind::LeftParenthesis,
+                    TokenKind::LeftCurlyBrace,
+                    TokenKind::Semicolon,
+                ],
+                actual: self.current_token.to_owned(),
+                position: self.current_position,
+            });
         }
 
         let expression = self.parse_expression(0)?;
@@ -569,6 +614,51 @@ impl<'src> Parser<'src> {
                     expressions.push(expression);
                 }
             }
+            Token::Map => {
+                self.next_token()?;
+
+                if let Token::LeftCurlyBrace = self.current_token {
+                    self.next_token()?;
+                } else {
+                    return Err(ParseError::ExpectedToken {
+                        expected: TokenKind::LeftCurlyBrace,
+                        actual: self.current_token.to_owned(),
+                        position: self.current_position,
+                    });
+                }
+
+                let mut fields = Vec::new();
+
+                loop {
+                    if let Token::RightCurlyBrace = self.current_token {
+                        let position = (start_position.0, self.current_position.1);
+
+                        self.next_token()?;
+
+                        return Ok(Expression::map(fields, position));
+                    }
+
+                    let field_name = self.parse_identifier()?;
+
+                    if let Token::Equal = self.current_token {
+                        self.next_token()?;
+                    } else {
+                        return Err(ParseError::ExpectedToken {
+                            expected: TokenKind::Equal,
+                            actual: self.current_token.to_owned(),
+                            position: self.current_position,
+                        });
+                    }
+
+                    let field_value = self.parse_expression(0)?;
+
+                    fields.push((field_name, field_value));
+
+                    if let Token::Comma = self.current_token {
+                        self.next_token()?;
+                    }
+                }
+            }
             Token::While => {
                 self.next_token()?;
 
@@ -1084,9 +1174,39 @@ mod tests {
     use super::*;
 
     #[test]
-    fn let_mut_while_loop() {
+    fn map_expression() {
-        env_logger::builder().is_test(true).try_init().ok();
+        let source = "map { x = '1', y = 2, z = 3.0 }";
 
+        assert_eq!(
+            parse(source),
+            Ok(AbstractSyntaxTree {
+                statements: [Statement::Expression(Expression::map(
+                    vec![
+                        (
+                            Node::new(Identifier::new("x"), (6, 7)),
+                            Expression::literal(
+                                LiteralExpression::String("1".to_string()),
+                                (10, 13)
+                            ),
+                        ),
+                        (
+                            Node::new(Identifier::new("y"), (15, 16)),
+                            Expression::literal(LiteralExpression::Integer(2), (19, 20)),
+                        ),
+                        (
+                            Node::new(Identifier::new("z"), (22, 23)),
+                            Expression::literal(LiteralExpression::Float(3.0), (26, 29)),
+                        ),
+                    ],
+                    (0, 31),
+                ))]
+                .into(),
+            })
+        );
+    }
+
+    #[test]
+    fn let_mut_while_loop() {
         let source = "let mut x = 0; while x < 10 { x += 1 }; x";
 
         assert_eq!(
@@ -1307,36 +1427,26 @@ mod tests {
 
     #[test]
     fn tuple_struct_instantiation() {
-        let source = "struct Foo(int, float) Foo(1, 2.0)";
+        let source = "Foo(1, 2.0)";
 
         assert_eq!(
             parse(source),
             Ok(AbstractSyntaxTree::with_statements([
-                Statement::struct_definition(
-                    StructDefinition::Tuple {
-                        name: Node::new(Identifier::new("Foo"), (7, 10)),
-                        items: vec![
-                            Node::new(Type::Integer, (11, 14)),
-                            Node::new(Type::Float, (16, 21)),
-                        ]
-                    },
-                    (0, 22)
-                ),
                 Statement::Expression(Expression::call(
-                    Expression::identifier(Identifier::new("Foo"), (23, 26)),
+                    Expression::identifier(Identifier::new("Foo"), (0, 3)),
                     vec![
-                        Expression::literal(LiteralExpression::Integer(1), (27, 28)),
+                        Expression::literal(LiteralExpression::Integer(1), (4, 5)),
-                        Expression::literal(LiteralExpression::Float(2.0), (30, 33))
+                        Expression::literal(LiteralExpression::Float(2.0), (7, 10))
                     ],
-                    (23, 34)
+                    (0, 11)
                 ))
             ]))
         );
     }
 
     #[test]
-    fn tuple_struct() {
+    fn tuple_struct_definition() {
-        let source = "struct Foo(int, float)";
+        let source = "struct Foo(int, float);";
 
         assert_eq!(
             parse(source),
@@ -1349,7 +1459,7 @@ mod tests {
                             Node::new(Type::Float, (16, 21)),
                         ],
                     },
-                    (0, 22)
+                    (0, 23)
                 ))
             ]))
         );
@@ -1357,7 +1467,7 @@ mod tests {
 
     #[test]
     fn unit_struct() {
-        let source = "struct Foo";
+        let source = "struct Foo;";
 
         assert_eq!(
             parse(source),
@@ -1366,7 +1476,7 @@ mod tests {
                     StructDefinition::Unit {
                         name: Node::new(Identifier::new("Foo"), (7, 10)),
                     },
-                    (0, 10)
+                    (0, 11)
                 ))
             ]))
         );

dust-lang/src/token.rs

@@ -27,6 +27,7 @@ pub enum Token<'src> {
     IsOdd,
     Length,
     Let,
+    Map,
     Mut,
     ReadLine,
     Str,
@@ -101,6 +102,7 @@ impl<'src> Token<'src> {
             Token::Let => TokenOwned::Let,
             Token::Less => TokenOwned::Less,
             Token::LessEqual => TokenOwned::LessOrEqual,
+            Token::Map => TokenOwned::Map,
             Token::Minus => TokenOwned::Minus,
             Token::MinusEqual => TokenOwned::MinusEqual,
             Token::Mut => TokenOwned::Mut,
@@ -159,6 +161,7 @@ impl<'src> Token<'src> {
             Token::Length => "length",
             Token::Less => "<",
             Token::LessEqual => "<=",
+            Token::Map => "map",
             Token::Minus => "-",
             Token::MinusEqual => "-=",
             Token::Mut => "mut",
@@ -214,6 +217,7 @@ impl<'src> Token<'src> {
             Token::Length => TokenKind::Length,
             Token::Less => TokenKind::Less,
             Token::LessEqual => TokenKind::LessOrEqual,
+            Token::Map => TokenKind::Map,
             Token::Minus => TokenKind::Minus,
             Token::MinusEqual => TokenKind::MinusEqual,
             Token::Mut => TokenKind::Mut,
@@ -320,6 +324,7 @@ pub enum TokenOwned {
     IsOdd,
     Let,
     Length,
+    Map,
     Mut,
     ReadLine,
     Str,
@@ -395,6 +400,7 @@ impl Display for TokenOwned {
             TokenOwned::Let => Token::Let.fmt(f),
             TokenOwned::Less => Token::Less.fmt(f),
             TokenOwned::LessOrEqual => Token::LessEqual.fmt(f),
+            TokenOwned::Map => Token::Map.fmt(f),
             TokenOwned::Minus => Token::Minus.fmt(f),
             TokenOwned::MinusEqual => Token::MinusEqual.fmt(f),
             TokenOwned::Mut => Token::Mut.fmt(f),
@@ -442,6 +448,7 @@ pub enum TokenKind {
     IsOdd,
     Length,
     Let,
+    Map,
     ReadLine,
     Str,
     ToString,
@@ -516,6 +523,7 @@ impl Display for TokenKind {
             TokenKind::Let => Token::Let.fmt(f),
             TokenKind::Less => Token::Less.fmt(f),
             TokenKind::LessOrEqual => Token::LessEqual.fmt(f),
+            TokenKind::Map => Token::Map.fmt(f),
             TokenKind::Minus => Token::Minus.fmt(f),
             TokenKind::MinusEqual => Token::MinusEqual.fmt(f),
             TokenKind::Mut => Token::Mut.fmt(f),
@@ -543,31 +551,17 @@ impl Display for TokenKind {
 pub(crate) mod tests {
     use super::*;
 
-    pub fn all_tokens<'src>() -> [Token<'src>; 51] {
+    pub fn all_tokens<'src>() -> [Token<'src>; 52] {
         [
-            Token::Eof,
+            Token::Identifier("foobar"),
-            Token::Identifier("identifier"),
             Token::Boolean("true"),
             Token::Float("1.0"),
             Token::Integer("1"),
             Token::String("string"),
             Token::Async,
-            Token::Bool,
-            Token::Else,
-            Token::FloatKeyword,
-            Token::If,
-            Token::Int,
-            Token::IsEven,
-            Token::IsOdd,
-            Token::Length,
-            Token::Let,
-            Token::ReadLine,
-            Token::Str,
-            Token::ToString,
-            Token::While,
-            Token::WriteLine,
-            Token::BangEqual,
             Token::Bang,
+            Token::BangEqual,
+            Token::Bool,
             Token::Colon,
             Token::Comma,
             Token::Dot,
@@ -575,27 +569,42 @@ pub(crate) mod tests {
             Token::DoubleDot,
             Token::DoubleEqual,
             Token::DoublePipe,
+            Token::Else,
+            Token::Eof,
             Token::Equal,
+            Token::FloatKeyword,
             Token::Greater,
             Token::GreaterEqual,
+            Token::If,
+            Token::Int,
+            Token::IsEven,
+            Token::IsOdd,
             Token::LeftCurlyBrace,
             Token::LeftParenthesis,
             Token::LeftSquareBrace,
+            Token::Length,
             Token::Less,
             Token::LessEqual,
+            Token::Let,
+            Token::Map,
             Token::Minus,
             Token::MinusEqual,
             Token::Mut,
             Token::Percent,
             Token::Plus,
             Token::PlusEqual,
+            Token::ReadLine,
             Token::RightCurlyBrace,
             Token::RightParenthesis,
             Token::RightSquareBrace,
             Token::Semicolon,
-            Token::Star,
-            Token::Struct,
             Token::Slash,
+            Token::Star,
+            Token::Str,
+            Token::Struct,
+            Token::ToString,
+            Token::While,
+            Token::WriteLine,
         ]
     }
 

dust-lang/src/type.rs

@@ -13,17 +13,16 @@ use std::{
     cmp::Ordering,
     collections::HashMap,
     fmt::{self, Display, Formatter},
-    sync::Arc,
 };
 
 use serde::{Deserialize, Serialize};
 
-use crate::{value::Function, Identifier};
+use crate::Identifier;
 
-#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
 /// Description of a kind of value.
 ///
 /// See the [module documentation](index.html) for more information.
+#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
 pub enum Type {
     Any,
     Boolean,
@@ -45,8 +44,13 @@ pub enum Type {
     ListOf {
         item_type: Box<Type>,
     },
+    Map {
+        pairs: HashMap<Identifier, Type>,
+    },
     Number,
-    Range,
+    Range {
+        r#type: RangeableType,
+    },
     String,
     Struct(StructType),
     Tuple(TupleType),
@@ -72,7 +76,6 @@ impl Type {
             | (Type::Boolean, Type::Boolean)
             | (Type::Float, Type::Float)
             | (Type::Integer, Type::Integer)
-            | (Type::Range, Type::Range)
             | (Type::String, Type::String) => return Ok(()),
             (
                 Type::Generic {
@@ -192,38 +195,21 @@ impl Type {
                     return_type: right_return,
                 }),
             ) => {
-                if left_name != right_name {
+                if left_name != right_name
-                    return Err(TypeConflict {
+                    || left_return != right_return
-                        actual: other.clone(),
+                    || left_type_parameters != right_type_parameters
-                        expected: self.clone(),
+                    || left_value_parameters != right_value_parameters
-                    });
-                }
-
-                if left_return == right_return {
-                    for (left_parameter, right_parameter) in left_type_parameters
-                        .iter()
-                        .zip(right_type_parameters.iter())
                 {
-                        if left_parameter != right_parameter {
                     return Err(TypeConflict {
                         actual: other.clone(),
                         expected: self.clone(),
                     });
                 }
-                    }
 
-                    for (left_parameter, right_parameter) in left_value_parameters
+                return Ok(());
-                        .iter()
-                        .zip(right_value_parameters.iter())
-                    {
-                        if left_parameter != right_parameter {
-                            return Err(TypeConflict {
-                                actual: other.clone(),
-                                expected: self.clone(),
-                            });
             }
-                    }
+            (Type::Range { r#type: left_type }, Type::Range { r#type: right_type }) => {
-
+                if left_type == right_type {
                     return Ok(());
                 }
             }
@@ -248,7 +234,7 @@ impl Display for Type {
             Type::Boolean => write!(f, "bool"),
             Type::Byte => write!(f, "byte"),
             Type::Character => write!(f, "char"),
-            Type::Enum(enum_type) => write!(f, "{enum_type}"),
+            Type::Enum(EnumType { name, .. }) => write!(f, "{name}"),
             Type::Float => write!(f, "float"),
             Type::Function(function_type) => write!(f, "{function_type}"),
             Type::Generic { concrete_type, .. } => {
@@ -262,10 +248,53 @@ impl Display for Type {
             Type::List { item_type, length } => write!(f, "[{item_type}; {length}]"),
             Type::ListEmpty => write!(f, "[]"),
             Type::ListOf { item_type } => write!(f, "[{item_type}]"),
+            Type::Map { pairs } => {
+                write!(f, "map ")?;
+
+                write!(f, "{{")?;
+
+                for (index, (key, value)) in pairs.iter().enumerate() {
+                    write!(f, "{key}: {value}")?;
+
+                    if index != pairs.len() - 1 {
+                        write!(f, ", ")?;
+                    }
+                }
+
+                write!(f, "}}")
+            }
             Type::Number => write!(f, "num"),
-            Type::Range => write!(f, "range"),
+            Type::Range { r#type } => write!(f, "{type} range"),
             Type::String => write!(f, "str"),
-            Type::Struct(struct_type) => write!(f, "{struct_type}"),
+            Type::Struct(struct_type) => match struct_type {
+                StructType::Unit => write!(f, "()"),
+                StructType::Tuple(TupleType { fields }) => {
+                    write!(f, "(")?;
+
+                    for (index, r#type) in fields.iter().enumerate() {
+                        write!(f, "{type}")?;
+
+                        if index != fields.len() - 1 {
+                            write!(f, ", ")?;
+                        }
+                    }
+
+                    write!(f, ")")
+                }
+                StructType::Fields(FieldsStructType { fields }) => {
+                    write!(f, "{{")?;
+
+                    for (index, (name, r#type)) in fields.iter().enumerate() {
+                        write!(f, "{name}: {type}")?;
+
+                        if index != fields.len() - 1 {
+                            write!(f, ", ")?;
+                        }
+                    }
+
+                    write!(f, "}}")
+                }
+            },
             Type::Tuple(TupleType { fields }) => {
                 write!(f, "(")?;
 
@@ -283,6 +312,85 @@ impl Display for Type {
     }
 }
 
+impl PartialOrd for Type {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Type {
+    fn cmp(&self, other: &Self) -> Ordering {
+        match (self, other) {
+            (Type::Any, Type::Any) => Ordering::Equal,
+            (Type::Any, _) => Ordering::Greater,
+            (Type::Boolean, Type::Boolean) => Ordering::Equal,
+            (Type::Boolean, _) => Ordering::Greater,
+            (Type::Byte, Type::Byte) => Ordering::Equal,
+            (Type::Byte, _) => Ordering::Greater,
+            (Type::Character, Type::Character) => Ordering::Equal,
+            (Type::Character, _) => Ordering::Greater,
+            (Type::Enum(left_enum), Type::Enum(right_enum)) => left_enum.cmp(right_enum),
+            (Type::Enum(_), _) => Ordering::Greater,
+            (Type::Float, Type::Float) => Ordering::Equal,
+            (Type::Float, _) => Ordering::Greater,
+            (Type::Function(left_function), Type::Function(right_function)) => {
+                left_function.cmp(right_function)
+            }
+            (Type::Function(_), _) => Ordering::Greater,
+            (Type::Generic { .. }, Type::Generic { .. }) => Ordering::Equal,
+            (Type::Generic { .. }, _) => Ordering::Greater,
+            (Type::Integer, Type::Integer) => Ordering::Equal,
+            (Type::Integer, _) => Ordering::Greater,
+            (
+                Type::List {
+                    item_type: left_item_type,
+                    length: left_length,
+                },
+                Type::List {
+                    item_type: right_item_type,
+                    length: right_length,
+                },
+            ) => {
+                if left_length == right_length {
+                    left_item_type.cmp(right_item_type)
+                } else {
+                    left_length.cmp(right_length)
+                }
+            }
+            (Type::List { .. }, _) => Ordering::Greater,
+            (Type::ListEmpty, Type::ListEmpty) => Ordering::Equal,
+            (Type::ListEmpty, _) => Ordering::Greater,
+            (
+                Type::ListOf {
+                    item_type: left_item_type,
+                },
+                Type::ListOf {
+                    item_type: right_item_type,
+                },
+            ) => left_item_type.cmp(right_item_type),
+            (Type::ListOf { .. }, _) => Ordering::Greater,
+            (Type::Map { pairs: left_pairs }, Type::Map { pairs: right_pairs }) => {
+                left_pairs.iter().cmp(right_pairs.iter())
+            }
+            (Type::Map { .. }, _) => Ordering::Greater,
+            (Type::Number, Type::Number) => Ordering::Equal,
+            (Type::Number, _) => Ordering::Greater,
+            (Type::Range { r#type: left_type }, Type::Range { r#type: right_type }) => {
+                left_type.cmp(right_type)
+            }
+            (Type::Range { .. }, _) => Ordering::Greater,
+            (Type::String, Type::String) => Ordering::Equal,
+            (Type::String, _) => Ordering::Greater,
+            (Type::Struct(left_struct), Type::Struct(right_struct)) => {
+                left_struct.cmp(right_struct)
+            }
+            (Type::Struct(_), _) => Ordering::Greater,
+            (Type::Tuple(left_tuple), Type::Tuple(right_tuple)) => left_tuple.cmp(right_tuple),
+            (Type::Tuple(_), _) => Ordering::Greater,
+        }
+    }
+}
+
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
 pub struct FunctionType {
     pub name: Identifier,
@@ -339,35 +447,11 @@ pub enum StructType {
 }
 
 impl Display for StructType {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
             StructType::Unit => write!(f, "()"),
-            StructType::Tuple(TupleType { fields, .. }) => {
+            StructType::Tuple(tuple) => write!(f, "{tuple}"),
-                write!(f, "(")?;
+            StructType::Fields(fields) => write!(f, "{fields}"),
-
-                for (index, r#type) in fields.iter().enumerate() {
-                    write!(f, "{type}")?;
-
-                    if index != fields.len() - 1 {
-                        write!(f, ", ")?;
-                    }
-                }
-
-                write!(f, ")")
-            }
-            StructType::Fields(FieldsStructType { fields, .. }) => {
-                write!(f, "{{ ")?;
-
-                for (index, (identifier, r#type)) in fields.iter().enumerate() {
-                    write!(f, "{identifier}: {type}")?;
-
-                    if index != fields.len() - 1 {
-                        write!(f, ", ")?;
-                    }
-                }
-
-                write!(f, " }}")
-            }
         }
     }
 }
@@ -377,11 +461,43 @@ pub struct TupleType {
     pub fields: Vec<Type>,
 }
 
+impl Display for TupleType {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "(")?;
+
+        for (index, field) in self.fields.iter().enumerate() {
+            write!(f, "{field}")?;
+
+            if index != self.fields.len() - 1 {
+                write!(f, ", ")?;
+            }
+        }
+
+        write!(f, ")")
+    }
+}
+
 #[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
 pub struct FieldsStructType {
     pub fields: HashMap<Identifier, Type>,
 }
 
+impl Display for FieldsStructType {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{{ ")?;
+
+        for (index, (identifier, r#type)) in self.fields.iter().enumerate() {
+            write!(f, "{identifier}: {type}")?;
+
+            if index != self.fields.len() - 1 {
+                write!(f, ", ")?;
+            }
+        }
+
+        write!(f, " }}")
+    }
+}
+
 impl PartialOrd for FieldsStructType {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))
@@ -401,8 +517,39 @@ pub struct EnumType {
 }
 
 impl Display for EnumType {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.name)
+        let EnumType { name, variants } = self;
+
+        write!(f, "enum {name} {{")?;
+
+        for (index, variant) in variants.iter().enumerate() {
+            write!(f, "{variant}")?;
+
+            if index != self.variants.len() - 1 {
+                write!(f, ", ")?;
+            }
+        }
+
+        write!(f, "}}")
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
+pub enum RangeableType {
+    Byte,
+    Character,
+    Float,
+    Integer,
+}
+
+impl Display for RangeableType {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            RangeableType::Byte => Type::Byte.fmt(f),
+            RangeableType::Character => Type::Character.fmt(f),
+            RangeableType::Float => Type::Float.fmt(f),
+            RangeableType::Integer => Type::Integer.fmt(f),
+        }
     }
 }
 
@@ -476,7 +623,9 @@ mod tests {
                 item_type: Box::new(Type::Integer),
                 length: 42,
             },
-            Type::Range,
+            Type::Range {
+                r#type: RangeableType::Integer,
+            },
             Type::String,
         ];
 

dust-lang/src/value.rs

@@ -4,19 +4,20 @@ use std::{
     collections::HashMap,
     error::Error,
     fmt::{self, Display, Formatter},
-    ops::{Range, RangeInclusive},
+    ops::{Index, Range, RangeInclusive},
+    rc::Weak,
     sync::{Arc, RwLock},
 };
 
 use serde::{
     de::{self, MapAccess, Visitor},
-    ser::{SerializeStruct, SerializeStructVariant},
+    ser::{SerializeMap, SerializeStruct, SerializeStructVariant},
     Deserialize, Deserializer, Serialize, Serializer,
 };
 
 use crate::{
     AbstractSyntaxTree, Context, EnumType, FieldsStructType, FunctionType, Identifier,
-    RuntimeError, StructType, TupleType, Type, Vm,
+    RangeableType, RuntimeError, StructType, TupleType, Type, Vm,
 };
 
 /// Dust value representation
@@ -61,6 +62,7 @@ pub enum Value {
     Function(Function),
     Integer(i64),
     List(Vec<Value>),
+    Map(HashMap<Identifier, Value>),
     Mutable(Arc<RwLock<Value>>),
     Range(Range<Rangeable>),
     RangeInclusive(RangeInclusive<Rangeable>),
@@ -70,6 +72,10 @@ pub enum Value {
 }
 
 impl Value {
+    pub fn map<T: Into<HashMap<Identifier, Value>>>(pairs: T) -> Value {
+        Value::Map(pairs.into())
+    }
+
     pub fn mutable(value: Value) -> Value {
         Value::Mutable(Arc::new(RwLock::new(value)))
     }
@@ -194,9 +200,25 @@ impl Value {
                     length: values.len(),
                 }
             }
+            Value::Map(map) => {
+                let pairs = map
+                    .iter()
+                    .map(|(key, value)| (key.clone(), value.r#type()))
+                    .collect();
+
+                Type::Map { pairs }
+            }
             Value::Mutable(locked) => locked.read().unwrap().r#type(),
-            Value::Range(_) => Type::Range,
+            Value::Range(range) => Type::Range {
-            Value::RangeInclusive(_) => Type::Range,
+                r#type: range.start.r#type(),
+            },
+            Value::RangeInclusive(range_inclusive) => {
+                let rangeable_type = range_inclusive.start().r#type();
+
+                Type::Range {
+                    r#type: rangeable_type,
+                }
+            }
             Value::String(_) => Type::String,
             Value::Struct(r#struct) => match r#struct {
                 Struct::Unit { .. } => Type::Struct(StructType::Unit),
@@ -230,12 +252,69 @@ impl Value {
         }
     }
 
-    pub fn get_index(&self, index: usize) -> Option<Value> {
+    pub fn get_index(&self, index: Value) -> Result<Option<Value>, ValueError> {
-        match self {
+        match (self, index) {
-            Value::List(values) => values.get(index).cloned(),
+            (Value::Mutable(left), Value::Mutable(right)) => {
-            Value::Mutable(inner) => inner.read().unwrap().get_index(index),
+                return left
-            Value::Struct(Struct::Tuple { fields, .. }) => fields.get(index).cloned(),
+                    .read()
-            _ => None,
+                    .unwrap()
+                    .get_index(right.read().unwrap().clone());
+            }
+            (Value::Mutable(locked), index) => {
+                return locked.read().unwrap().get_index(index);
+            }
+            (left, Value::Mutable(locked)) => {
+                return left.get_index(locked.read().unwrap().clone());
+            }
+            (Value::List(values), Value::Integer(integer)) => {
+                let index = integer as usize;
+
+                return Ok(values.get(index).cloned());
+            }
+            (Value::List(values), Value::Range(range)) => match (range.start, range.end) {
+                (Rangeable::Integer(start), Rangeable::Integer(end)) => {
+                    let start = start as usize;
+                    let end = end as usize;
+
+                    return Ok(values
+                        .get(start..end)
+                        .map(|values| Value::List(values.to_vec())));
+                }
+                (start, end) => Err(ValueError::CannotIndex {
+                    value: self.clone(),
+                    index: Value::Range(start..end),
+                }),
+            },
+            (Value::String(string), Value::Range(range)) => match (range.start, range.end) {
+                (Rangeable::Integer(start), Rangeable::Integer(end)) => {
+                    let start = start as usize;
+                    let end = end as usize;
+
+                    return Ok(string.get(start..end).map(Value::string));
+                }
+                (start, end) => Err(ValueError::CannotIndex {
+                    value: self.clone(),
+                    index: Value::Range(start..end),
+                }),
+            },
+            (Value::Range(range), Value::Integer(index)) => match (range.start, range.end) {
+                (Rangeable::Integer(start), Rangeable::Integer(end)) => {
+                    Ok((start..end).nth(index as usize).map(Value::Integer))
+                }
+                (start, end) => Err(ValueError::CannotIndex {
+                    value: self.clone(),
+                    index: Value::Range(start..end),
+                }),
+            },
+            (Value::String(string), Value::Integer(integer)) => {
+                let index = integer as usize;
+
+                return Ok(string.chars().nth(index).map(Value::Character));
+            }
+            (value, index) => Err(ValueError::CannotIndex {
+                value: value.clone(),
+                index,
+            }),
         }
     }
 
@@ -295,7 +374,7 @@ impl Value {
             _ => {}
         }
 
-        Err(ValueError::CannotAdd(self.clone(), other.clone()))
+        Err(ValueError::CannotMutate(self.clone()))
     }
 
     pub fn subtract(&self, other: &Value) -> Result<Value, ValueError> {
@@ -698,6 +777,19 @@ impl Display for Value {
             Value::Float(float) => write!(f, "{float}"),
             Value::Function(function) => write!(f, "{function}"),
             Value::Integer(integer) => write!(f, "{integer}"),
+            Value::Map(pairs) => {
+                write!(f, "{{ ")?;
+
+                for (index, (key, value)) in pairs.iter().enumerate() {
+                    write!(f, "{key}: {value}")?;
+
+                    if index < pairs.len() - 1 {
+                        write!(f, ", ")?;
+                    }
+                }
+
+                write!(f, " }}")
+            }
             Value::List(list) => {
                 write!(f, "[")?;
 
@@ -751,6 +843,7 @@ impl PartialEq for Value {
             (Value::Function(left), Value::Function(right)) => left == right,
             (Value::Integer(left), Value::Integer(right)) => left == right,
             (Value::List(left), Value::List(right)) => left == right,
+            (Value::Map(left), Value::Map(right)) => left == right,
             (Value::Mutable(left), Value::Mutable(right)) => {
                 let left = &*left.read().unwrap();
                 let right = &*right.read().unwrap();
@@ -853,6 +946,15 @@ impl Serialize for Value {
             Value::Function(function) => function.serialize(serializer),
             Value::Integer(integer) => serializer.serialize_i64(*integer),
             Value::List(list) => list.serialize(serializer),
+            Value::Map(pairs) => {
+                let mut ser = serializer.serialize_map(Some(pairs.len()))?;
+
+                for (key, value) in pairs {
+                    ser.serialize_entry(key, value)?;
+                }
+
+                ser.end()
+            }
             Value::Range(range) => range.serialize(serializer),
             Value::RangeInclusive(inclusive) => inclusive.serialize(serializer),
             Value::String(string) => serializer.serialize_str(string),
@@ -1033,7 +1135,7 @@ impl<'de> Deserialize<'de> for Function {
                                 return Err(de::Error::duplicate_field("body"));
                             }
 
-                            body = Some(map.next_value().map(|ast| Arc::new(ast))?);
+                            body = Some(map.next_value().map(Arc::new)?);
                         }
                         _ => {
                             return Err(de::Error::unknown_field(key, &["name", "type", "body"]));
@@ -1156,7 +1258,7 @@ impl Display for Struct {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
 pub enum Rangeable {
     Byte(u8),
     Character(char),
@@ -1164,6 +1266,17 @@ pub enum Rangeable {
     Integer(i64),
 }
 
+impl Rangeable {
+    fn r#type(&self) -> RangeableType {
+        match self {
+            Rangeable::Byte(_) => RangeableType::Byte,
+            Rangeable::Character(_) => RangeableType::Character,
+            Rangeable::Float(_) => RangeableType::Float,
+            Rangeable::Integer(_) => RangeableType::Integer,
+        }
+    }
+}
+
 impl Display for Rangeable {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         match self {

dust-lang/src/vm.rs

@@ -5,6 +5,7 @@
 //! - `run_with_context` convenience function that takes a source code string and a context
 //! - `Vm` struct that can be used to run an abstract syntax tree
 use std::{
+    collections::HashMap,
     fmt::{self, Display, Formatter},
     sync::{Arc, Mutex},
 };
@@ -15,11 +16,11 @@ use crate::{
     ast::{
         AbstractSyntaxTree, BlockExpression, CallExpression, ComparisonOperator, ElseExpression,
         FieldAccessExpression, IfExpression, LetStatement, ListExpression, ListIndexExpression,
-        LiteralExpression, LogicOperator, LoopExpression, MathOperator, Node, OperatorExpression,
+        LiteralExpression, LogicOperator, LoopExpression, MapExpression, MathOperator, Node,
-        RangeExpression, Span, Statement, StructDefinition,
+        OperatorExpression, RangeExpression, Span, Statement, StructDefinition, StructExpression,
     },
-    parse, Analyzer, BuiltInFunctionError, Context, DustError, Expression, Identifier, ParseError,
+    parse, Analyzer, BuiltInFunctionError, Context, DustError, Expression, FieldsStructType,
-    StructType, TupleType, Type, Value, ValueError,
+    Identifier, ParseError, Struct, StructType, TupleType, Type, Value, ValueError,
 };
 
 /// Run the source code and return the result.
@@ -129,7 +130,17 @@ impl Vm {
 
                         (name.inner.clone(), StructType::Tuple(TupleType { fields }))
                     }
-                    StructDefinition::Fields { name, fields } => todo!(),
+                    StructDefinition::Fields { name, fields } => {
+                        let fields = fields
+                            .into_iter()
+                            .map(|(identifier, r#type)| (identifier.inner, r#type.inner))
+                            .collect();
+
+                        (
+                            name.inner.clone(),
+                            StructType::Fields(FieldsStructType { fields }),
+                        )
+                    }
                 };
 
                 self.context
@@ -202,7 +213,7 @@ impl Vm {
                 if let Some(value) = get_value {
                     Ok(Evaluation::Return(Some(value)))
                 } else {
-                    Err(RuntimeError::UndefinedVariable {
+                    Err(RuntimeError::UndefinedValue {
                         identifier: identifier.inner,
                         position: identifier.position,
                     })
@@ -217,10 +228,99 @@ impl Vm {
             }
             Expression::Literal(literal) => self.run_literal(*literal.inner),
             Expression::Loop(loop_expression) => self.run_loop(*loop_expression.inner),
+            Expression::Map(map_expression) => self.run_map(*map_expression.inner, collect_garbage),
             Expression::Operator(operator_expression) => {
                 self.run_operator(*operator_expression.inner, collect_garbage)
             }
-            Expression::Range(range_expression) => match *range_expression.inner {
+            Expression::Range(range_expression) => {
+                self.run_range(*range_expression.inner, collect_garbage)
+            }
+            Expression::Struct(struct_expression) => {
+                self.run_struct(*struct_expression.inner, collect_garbage)
+            }
+            Expression::TupleAccess(_) => todo!(),
+        };
+
+        evaluation_result.map_err(|error| RuntimeError::Trace {
+            error: Box::new(error),
+            position,
+        })
+    }
+
+    fn run_struct(
+        &self,
+        struct_expression: StructExpression,
+        collect_garbage: bool,
+    ) -> Result<Evaluation, RuntimeError> {
+        match struct_expression {
+            StructExpression::Unit { name } => {
+                let position = name.position;
+                let r#type = self.context.get_type(&name.inner).ok_or_else(|| {
+                    RuntimeError::UndefinedType {
+                        identifier: name.inner.clone(),
+                        position,
+                    }
+                })?;
+
+                if let Type::Struct(StructType::Unit) = r#type {
+                    Ok(Evaluation::Return(Some(Value::Struct(Struct::Unit {
+                        name: name.inner,
+                    }))))
+                } else {
+                    Err(RuntimeError::ExpectedType {
+                        expected: Type::Struct(StructType::Unit),
+                        actual: r#type,
+                        position,
+                    })
+                }
+            }
+            StructExpression::Fields {
+                name,
+                fields: expressions,
+            } => {
+                let position = name.position;
+                let r#type = self.context.get_type(&name.inner).ok_or_else(|| {
+                    RuntimeError::UndefinedType {
+                        identifier: name.inner.clone(),
+                        position,
+                    }
+                })?;
+
+                if let Type::Struct(StructType::Fields(FieldsStructType { .. })) = r#type {
+                    let mut values = HashMap::with_capacity(expressions.len());
+
+                    for (identifier, expression) in expressions {
+                        let expression_position = expression.position();
+                        let value = self
+                            .run_expression(expression, collect_garbage)?
+                            .expect_value(expression_position)?;
+
+                        values.insert(identifier.inner, value);
+                    }
+
+                    Ok(Evaluation::Return(Some(Value::Struct(Struct::Fields {
+                        name: name.inner,
+                        fields: values,
+                    }))))
+                } else {
+                    Err(RuntimeError::ExpectedType {
+                        expected: Type::Struct(StructType::Fields(FieldsStructType {
+                            fields: HashMap::new(),
+                        })),
+                        actual: r#type,
+                        position,
+                    })
+                }
+            }
+        }
+    }
+
+    fn run_range(
+        &self,
+        range: RangeExpression,
+        collect_garbage: bool,
+    ) -> Result<Evaluation, RuntimeError> {
+        match range {
             RangeExpression::Exclusive { start, end } => {
                 let start_position = start.position();
                 let start = self
@@ -270,24 +370,37 @@ impl Vm {
                     (Value::Float(start), Value::Float(end)) => Ok(Evaluation::Return(Some(
                         Value::float_range_inclusive(start, end),
                     ))),
-                        (Value::Integer(start), Value::Integer(end)) => Ok(Evaluation::Return(
+                    (Value::Integer(start), Value::Integer(end)) => Ok(Evaluation::Return(Some(
-                            Some(Value::integer_range_inclusive(start, end)),
+                        Value::integer_range_inclusive(start, end),
-                        )),
+                    ))),
                     _ => Err(RuntimeError::InvalidRange {
                         start_position,
                         end_position,
                     }),
                 }
             }
-            },
+        }
-            Expression::Struct(_) => todo!(),
+    }
-            Expression::TupleAccess(_) => todo!(),
-        };
 
-        evaluation_result.map_err(|error| RuntimeError::Trace {
+    fn run_map(
-            error: Box::new(error),
+        &self,
-            position,
+        map: MapExpression,
-        })
+        collect_garbage: bool,
+    ) -> Result<Evaluation, RuntimeError> {
+        let MapExpression { pairs } = map;
+
+        let mut map = HashMap::new();
+
+        for (identifier, expression) in pairs {
+            let expression_position = expression.position();
+            let value = self
+                .run_expression(expression, collect_garbage)?
+                .expect_value(expression_position)?;
+
+            map.insert(identifier.inner, value);
+        }
+
+        Ok(Evaluation::Return(Some(Value::Map(map))))
     }
 
     fn run_operator(
@@ -530,17 +643,16 @@ impl Vm {
             .run_expression(index, collect_garbage)?
             .expect_value(index_position)?;
 
-        let index = if let Some(index) = index_value.as_integer() {
+        let get_index =
-            index as usize
+            list_value
-        } else {
+                .get_index(index_value)
-            return Err(RuntimeError::ExpectedInteger {
+                .map_err(|error| RuntimeError::ValueError {
-                position: index_position,
+                    error,
-            });
+                    left_position: list_position,
-        };
+                    right_position: index_position,
+                })?;
 
-        let value_option = list_value.get_index(index);
+        Ok(Evaluation::Return(get_index))
-
-        Ok(Evaluation::Return(value_option))
     }
 
     fn run_call(
@@ -797,10 +909,6 @@ pub enum RuntimeError {
         error: BuiltInFunctionError,
         position: Span,
     },
-    CannotMutate {
-        value: Value,
-        position: Span,
-    },
     ExpectedBoolean {
         position: Span,
     },
@@ -822,6 +930,11 @@ pub enum RuntimeError {
     ExpectedMap {
         position: Span,
     },
+    ExpectedType {
+        expected: Type,
+        actual: Type,
+        position: Span,
+    },
     ExpectedFunction {
         actual: Value,
         position: Span,
@@ -836,7 +949,11 @@ pub enum RuntimeError {
         start_position: Span,
         end_position: Span,
     },
-    UndefinedVariable {
+    UndefinedType {
+        identifier: Identifier,
+        position: Span,
+    },
+    UndefinedValue {
         identifier: Identifier,
         position: Span,
     },
@@ -859,23 +976,24 @@ impl RuntimeError {
                 ..
             } => (left_position.0, right_position.1),
             Self::BuiltInFunctionError { position, .. } => *position,
-            Self::CannotMutate { position, .. } => *position,
             Self::ExpectedBoolean { position } => *position,
+            Self::ExpectedFunction { position, .. } => *position,
             Self::ExpectedIdentifier { position } => *position,
-            Self::ExpectedIntegerOrRange { position } => *position,
             Self::ExpectedIdentifierOrString { position } => *position,
             Self::ExpectedInteger { position } => *position,
-            Self::ExpectedNumber { position } => *position,
+            Self::ExpectedIntegerOrRange { position } => *position,
-            Self::ExpectedMap { position } => *position,
-            Self::ExpectedFunction { position, .. } => *position,
             Self::ExpectedList { position } => *position,
+            Self::ExpectedMap { position } => *position,
+            Self::ExpectedNumber { position } => *position,
+            Self::ExpectedType { position, .. } => *position,
             Self::ExpectedValue { position } => *position,
             Self::InvalidRange {
                 start_position,
                 end_position,
                 ..
             } => (start_position.0, end_position.1),
-            Self::UndefinedVariable { position, .. } => *position,
+            Self::UndefinedType { position, .. } => *position,
+            Self::UndefinedValue { position, .. } => *position,
             Self::UndefinedProperty {
                 property_position, ..
             } => *property_position,
@@ -911,9 +1029,6 @@ impl Display for RuntimeError {
                     left_position, right_position, error
                 )
             }
-            Self::CannotMutate { value, .. } => {
-                write!(f, "Cannot mutate immutable value {}", value)
-            }
             Self::BuiltInFunctionError { error, .. } => {
                 write!(f, "{}", error)
             }
@@ -950,6 +1065,17 @@ impl Display for RuntimeError {
             Self::ExpectedList { position } => {
                 write!(f, "Expected a list at position: {:?}", position)
             }
+            Self::ExpectedType {
+                expected,
+                actual,
+                position,
+            } => {
+                write!(
+                    f,
+                    "Expected type {}, but got {} at position: {:?}",
+                    expected, actual, position
+                )
+            }
             Self::ExpectedMap { position } => {
                 write!(f, "Expected a map at position: {:?}", position)
             }
@@ -973,7 +1099,7 @@ impl Display for RuntimeError {
                     start_position, end_position
                 )
             }
-            Self::UndefinedVariable {
+            Self::UndefinedValue {
                 identifier,
                 position,
             } => {
@@ -988,6 +1114,16 @@ impl Display for RuntimeError {
             } => {
                 write!(f, "Value {} does not have the property {}", value, property)
             }
+            Self::UndefinedType {
+                identifier,
+                position,
+            } => {
+                write!(
+                    f,
+                    "Undefined type {} at position: {:?}",
+                    identifier, position
+                )
+            }
         }
     }
 }
@@ -1001,10 +1137,30 @@ mod tests {
     use super::*;
 
     #[test]
-    fn async_block() {
+    fn string_index() {
-        let input = "let x = 1; async { x += 1; x -= 1; } x";
+        let input = "'foo'[0]";
 
-        assert_eq!(run(input), Ok(Some(Value::Integer(1))));
+        assert_eq!(run(input), Ok(Some(Value::Character('f'))));
+    }
+
+    #[test]
+    fn map_expression() {
+        let input = "let x = map { foo = 42, bar = 4.2 }; x";
+
+        assert_eq!(
+            run(input),
+            Ok(Some(Value::map([
+                (Identifier::new("foo"), Value::Integer(42)),
+                (Identifier::new("bar"), Value::Float(4.2))
+            ])))
+        );
+    }
+
+    #[test]
+    fn async_block() {
+        let input = "let mut x = 1; async { x += 1; x -= 1; } x";
+
+        assert_eq!(run(input), Ok(Some(Value::mutable(Value::Integer(1)))));
     }
 
     #[test]
@@ -1056,8 +1212,8 @@ mod tests {
     #[test]
     fn assign_unit_struct_variable() {
         let input = "
-            struct Foo
+            struct Foo;
-            x = Foo
+            let x = Foo;
             x
         ";