Overhaul built-ins and identifiers

src/abstract_tree/assignment.rs

@@ -54,14 +54,13 @@ impl AbstractTree for Assignment {
 
     fn validate(&self, source: &str, context: &Context) -> Result<(), ValidationError> {
         if let AssignmentOperator::Equal = self.operator {
-            let key = self.identifier.inner().clone();
             let r#type = if let Some(definition) = &self.type_specification {
                 definition.inner().clone()
             } else {
                 self.statement.expected_type(context)?
             };
 
-            context.set_type(key, r#type)?;
+            context.set_type(self.identifier.clone(), r#type)?;
         }
 
         if let Some(type_specification) = &self.type_specification {
@@ -130,30 +129,33 @@ impl AbstractTree for Assignment {
     }
 
     fn run(&self, source: &str, context: &Context) -> Result<Value, RuntimeError> {
-        let key = self.identifier.inner();
         let value = self.statement.run(source, context)?;
 
         let new_value = match self.operator {
             AssignmentOperator::PlusEqual => {
-                if let Some(mut previous_value) = context.get_value(key)? {
+                if let Some(mut previous_value) = context.get_value(&self.identifier)? {
                     previous_value += value;
                     previous_value
                 } else {
-                    return Err(RuntimeError::VariableIdentifierNotFound(key.clone()));
+                    return Err(RuntimeError::VariableIdentifierNotFound(
+                        self.identifier.clone(),
+                    ));
                 }
             }
             AssignmentOperator::MinusEqual => {
-                if let Some(mut previous_value) = context.get_value(key)? {
+                if let Some(mut previous_value) = context.get_value(&self.identifier)? {
                     previous_value -= value;
                     previous_value
                 } else {
-                    return Err(RuntimeError::VariableIdentifierNotFound(key.clone()));
+                    return Err(RuntimeError::VariableIdentifierNotFound(
+                        self.identifier.clone(),
+                    ));
                 }
             }
             AssignmentOperator::Equal => value,
         };
 
-        context.set_value(key.clone(), new_value)?;
+        context.set_value(self.identifier.clone(), new_value)?;
 
         Ok(Value::none())
     }

src/abstract_tree/enum_defintion.rs

@@ -27,8 +27,8 @@ impl EnumDefinition {
         }
     }
 
-    pub fn instantiate(&self, variant: String, content: Option<Value>) -> EnumInstance {
+    pub fn instantiate(&self, variant: Identifier, content: Option<Value>) -> EnumInstance {
-        EnumInstance::new(self.identifier.inner().clone(), variant, content)
+        EnumInstance::new(self.identifier.clone(), variant, content)
     }
 
     pub fn identifier(&self) -> &Identifier {
@@ -86,10 +86,7 @@ impl AbstractTree for EnumDefinition {
     }
 
     fn run(&self, _source: &str, context: &Context) -> Result<Value, RuntimeError> {
-        context.set_definition(
+        context.set_definition(self.identifier.clone(), TypeDefinition::Enum(self.clone()))?;
-            self.identifier.inner().clone(),
-            TypeDefinition::Enum(self.clone()),
-        )?;
 
         Ok(Value::none())
     }

src/abstract_tree/for.rs

@@ -76,7 +76,7 @@ impl AbstractTree for For {
                 position: self.source_position,
             });
         };
-        let key = self.item_id.inner().clone();
+        let key = self.item_id.clone();
 
         self.context.inherit_from(context)?;
         self.context.set_type(key, item_type)?;
@@ -87,7 +87,7 @@ impl AbstractTree for For {
         self.context.inherit_from(context)?;
 
         let expression_run = self.collection.run(source, context)?;
-        let key = self.item_id.inner();
+        let key = &self.item_id;
 
         if let Value::Range(range) = expression_run {
             if self.is_async {

src/abstract_tree/function_call.rs

@@ -142,16 +142,11 @@ impl AbstractTree for FunctionCall {
     fn run(&self, source: &str, context: &Context) -> Result<Value, RuntimeError> {
         let value = match &self.function_expression {
             FunctionExpression::Identifier(identifier) => {
-                let key = identifier.inner();
+                if let Some(value) = context.get_value(identifier)? {
-
+                    self.context.set_value(identifier.clone(), value.clone())?;
-                if let Some(value) = context.get_value(key)? {
-                    self.context
-                        .set_value(identifier.inner().clone(), value.clone())?;
                     value.clone()
                 } else {
-                    return Err(RuntimeError::VariableIdentifierNotFound(
+                    return Err(RuntimeError::VariableIdentifierNotFound(identifier.clone()));
-                        identifier.inner().clone(),
-                    ));
                 }
             }
             FunctionExpression::FunctionCall(function_call) => {
@@ -181,7 +176,7 @@ impl AbstractTree for FunctionCall {
                 for (identifier, expression) in parameter_expression_pairs {
                     let value = expression.run(source, context)?;
 
-                    self.context.set_value(identifier.inner().clone(), value)?;
+                    self.context.set_value(identifier.clone(), value)?;
                 }
 
                 function_node.call(source, &self.context)

src/abstract_tree/function_node.rs

@@ -118,7 +118,7 @@ impl AbstractTree for FunctionNode {
             let validation_context = Context::new();
 
             for (parameter, r#type) in self.parameters.iter().zip(parameter_types.iter()) {
-                validation_context.set_type(parameter.inner().clone(), r#type.clone())?;
+                validation_context.set_type(parameter.clone(), r#type.clone())?;
             }
 
             let actual = self.body.expected_type(&validation_context)?;

src/abstract_tree/identifier.rs

@@ -1,8 +1,12 @@
-use std::fmt::{self, Display, Formatter};
+use std::{
+    fmt::{self, Display, Formatter},
+    sync::Arc,
+};
 
-use serde::{Deserialize, Serialize};
+use serde::{de::Visitor, Deserialize, Serialize};
 
 use crate::{
+    built_in_identifiers::all_built_in_identifiers,
     error::{RuntimeError, SyntaxError, ValidationError},
     AbstractTree, Context, Format, SyntaxNode, Type, Value,
 };
@@ -10,22 +14,30 @@ use crate::{
 /// A string by which a variable is known to a context.
 ///
 /// Every variable is a key-value pair. An identifier holds the key part of that
-/// pair. Its inner value can be used to retrieve a Value instance from a Map.
+/// pair and can be used to retrieve a Value instance from a Map or Context.
-#[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord, Hash)]
+#[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
-pub struct Identifier(String);
+pub struct Identifier(Arc<String>);
 
 impl Identifier {
-    pub fn new<T: Into<String>>(inner: T) -> Self {
+    pub fn new(key: &str) -> Self {
-        Identifier(inner.into())
+        for built_in_identifier in all_built_in_identifiers() {
+            let identifier = built_in_identifier.get();
+
+            if &key == identifier.inner().as_ref() {
+                return identifier.clone();
+            }
+        }
+
+        Identifier(Arc::new(key.to_string()))
     }
 
-    pub fn take_inner(self) -> String {
+    pub fn inner(&self) -> &Arc<String> {
-        self.0
-    }
-
-    pub fn inner(&self) -> &String {
         &self.0
     }
+
+    pub fn contains(&self, string: &str) -> bool {
+        self.0.as_ref() == string
+    }
 }
 
 impl AbstractTree for Identifier {
@@ -40,7 +52,7 @@ impl AbstractTree for Identifier {
 
         debug_assert!(!text.is_empty());
 
-        Ok(Identifier(text.to_string()))
+        Ok(Identifier::new(text))
     }
 
     fn validate(&self, _source: &str, _context: &Context) -> Result<(), ValidationError> {
@@ -48,7 +60,7 @@ impl AbstractTree for Identifier {
     }
 
     fn expected_type(&self, context: &Context) -> Result<Type, ValidationError> {
-        if let Some(r#type) = context.get_type(&self.0)? {
+        if let Some(r#type) = context.get_type(self)? {
             Ok(r#type)
         } else {
             Err(ValidationError::VariableIdentifierNotFound(self.clone()))
@@ -56,10 +68,10 @@ impl AbstractTree for Identifier {
     }
 
     fn run(&self, _source: &str, context: &Context) -> Result<Value, RuntimeError> {
-        if let Some(value) = context.get_value(&self.0)? {
+        if let Some(value) = context.get_value(self)? {
             Ok(value.clone())
         } else {
-            Err(RuntimeError::VariableIdentifierNotFound(self.0.clone()))
+            Err(RuntimeError::VariableIdentifierNotFound(self.clone()))
         }
     }
 }
@@ -75,3 +87,38 @@ impl Display for Identifier {
         write!(f, "{}", self.0)
     }
 }
+
+impl Serialize for Identifier {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_str(self.0.as_ref())
+    }
+}
+
+impl<'de> Deserialize<'de> for Identifier {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        deserializer.deserialize_string(IdentifierVisitor)
+    }
+}
+
+struct IdentifierVisitor;
+
+impl<'de> Visitor<'de> for IdentifierVisitor {
+    type Value = Identifier;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("valid UFT-8 sequence")
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        Ok(Identifier(Arc::new(v)))
+    }
+}

src/abstract_tree/index.rs

@@ -2,7 +2,8 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     error::{RuntimeError, SyntaxError, ValidationError},
-    AbstractTree, Context, Format, IndexExpression, List, SourcePosition, SyntaxNode, Type, Value,
+    AbstractTree, Context, Format, Identifier, IndexExpression, SourcePosition, SyntaxNode, Type,
+    Value,
 };
 
 /// Abstract representation of an index expression.
@@ -12,7 +13,6 @@ use crate::{
 pub struct Index {
     pub collection: IndexExpression,
     pub index: IndexExpression,
-    pub index_end: Option<IndexExpression>,
     source_position: SourcePosition,
 }
 
@@ -26,21 +26,9 @@ impl AbstractTree for Index {
         let index_node = node.child(2).unwrap();
         let index = IndexExpression::from_syntax(index_node, source, context)?;
 
-        let index_end_node = node.child(4);
-        let index_end = if let Some(index_end_node) = index_end_node {
-            Some(IndexExpression::from_syntax(
-                index_end_node,
-                source,
-                context,
-            )?)
-        } else {
-            None
-        };
-
         Ok(Index {
             collection,
             index,
-            index_end,
             source_position: SourcePosition::from(node.range()),
         })
     }
@@ -58,10 +46,6 @@ impl AbstractTree for Index {
         self.collection.validate(_source, _context)?;
         self.index.validate(_source, _context)?;
 
-        if let Some(index_end) = &self.index_end {
-            index_end.validate(_source, _context)?;
-        }
-
         Ok(())
     }
 
@@ -71,36 +55,28 @@ impl AbstractTree for Index {
         match value {
             Value::List(list) => {
                 let index = self.index.run(source, context)?.as_integer()? as usize;
-
+                let item = list.items().get(index).cloned().unwrap_or_default();
-                let item = if let Some(index_end) = &self.index_end {
-                    let index_end = index_end.run(source, context)?.as_integer()? as usize;
-                    let sublist = list.items()[index..=index_end].to_vec();
-
-                    Value::List(List::with_items(sublist))
-                } else {
-                    list.items().get(index).cloned().unwrap_or_default()
-                };
 
                 Ok(item)
             }
             Value::Map(map) => {
                 let map = map.inner();
 
-                let (key, value) = if let IndexExpression::Identifier(identifier) = &self.index {
+                let (identifier, value) =
-                    let key = identifier.inner();
+                    if let IndexExpression::Identifier(identifier) = &self.index {
-                    let value = map.get(key).unwrap_or_default();
+                        let value = map.get(identifier).unwrap_or_default();
 
-                    (key.clone(), value)
+                        (identifier.clone(), value)
-                } else {
+                    } else {
-                    let index_value = self.index.run(source, context)?;
+                        let index_value = self.index.run(source, context)?;
-                    let key = index_value.as_string()?;
+                        let identifier = Identifier::new(index_value.as_string()?);
-                    let value = map.get(key.as_str()).unwrap_or_default();
+                        let value = map.get(&identifier).unwrap_or_default();
 
-                    (key.clone(), value)
+                        (identifier, value)
-                };
+                    };
 
                 if value.is_none() {
-                    Err(RuntimeError::VariableIdentifierNotFound(key))
+                    Err(RuntimeError::VariableIdentifierNotFound(identifier))
                 } else {
                     Ok(value.clone())
                 }
@@ -121,10 +97,5 @@ impl Format for Index {
         self.collection.format(output, indent_level);
         output.push(':');
         self.index.format(output, indent_level);
-
-        if let Some(expression) = &self.index_end {
-            output.push_str("..");
-            expression.format(output, indent_level);
-        }
     }
 }

src/abstract_tree/index_assignment.rs

@@ -2,8 +2,8 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     error::{RuntimeError, SyntaxError, ValidationError},
-    AbstractTree, AssignmentOperator, Context, Format, Index, IndexExpression, Statement,
+    AbstractTree, AssignmentOperator, Context, Format, Identifier, Index, IndexExpression,
-    SyntaxNode, Type, Value,
+    Statement, SyntaxNode, Type, Value,
 };
 
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
@@ -44,11 +44,14 @@ impl AbstractTree for IndexAssignment {
 
     fn run(&self, source: &str, context: &Context) -> Result<Value, RuntimeError> {
         let _index_collection = self.index.collection.run(source, context)?;
-        let index_key = if let IndexExpression::Identifier(identifier) = &self.index.index {
+        let index_identifier = if let IndexExpression::Identifier(identifier) = &self.index.index {
-            identifier.inner()
+            identifier
         } else {
+            let index_run = self.index.index.run(source, context)?;
+            let expected_identifier = Identifier::new(index_run.as_string()?);
+
             return Err(RuntimeError::VariableIdentifierNotFound(
-                self.index.index.run(source, context)?.to_string(),
+                expected_identifier,
             ));
         };
 
@@ -56,7 +59,7 @@ impl AbstractTree for IndexAssignment {
 
         let new_value = match self.operator {
             AssignmentOperator::PlusEqual => {
-                if let Some(mut previous_value) = context.get_value(index_key)? {
+                if let Some(mut previous_value) = context.get_value(index_identifier)? {
                     previous_value += value;
                     previous_value
                 } else {
@@ -64,7 +67,7 @@ impl AbstractTree for IndexAssignment {
                 }
             }
             AssignmentOperator::MinusEqual => {
-                if let Some(mut previous_value) = context.get_value(index_key)? {
+                if let Some(mut previous_value) = context.get_value(index_identifier)? {
                     previous_value -= value;
                     previous_value
                 } else {
@@ -74,7 +77,7 @@ impl AbstractTree for IndexAssignment {
             AssignmentOperator::Equal => value,
         };
 
-        context.set_value(index_key.clone(), new_value)?;
+        context.set_value(index_identifier.clone(), new_value)?;
 
         Ok(Value::none())
     }

src/abstract_tree/map_node.rs

@@ -11,12 +11,12 @@ use crate::{
 
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
 pub struct MapNode {
-    properties: BTreeMap<String, (Statement, Option<Type>)>,
+    properties: BTreeMap<Identifier, (Statement, Option<Type>)>,
     position: SourcePosition,
 }
 
 impl MapNode {
-    pub fn properties(&self) -> &BTreeMap<String, (Statement, Option<Type>)> {
+    pub fn properties(&self) -> &BTreeMap<Identifier, (Statement, Option<Type>)> {
         &self.properties
     }
 }
@@ -26,14 +26,14 @@ impl AbstractTree for MapNode {
         SyntaxError::expect_syntax_node(source, "map", node)?;
 
         let mut properties = BTreeMap::new();
-        let mut current_key = "".to_string();
+        let mut current_identifier = None;
         let mut current_type = None;
 
         for index in 0..node.child_count() - 1 {
             let child = node.child(index).unwrap();
 
             if child.kind() == "identifier" {
-                current_key = Identifier::from_syntax(child, source, context)?.take_inner();
+                current_identifier = Some(Identifier::from_syntax(child, source, context)?);
                 current_type = None;
             }
 
@@ -45,7 +45,9 @@ impl AbstractTree for MapNode {
             if child.kind() == "statement" {
                 let statement = Statement::from_syntax(child, source, context)?;
 
-                properties.insert(current_key.clone(), (statement, current_type.clone()));
+                if let Some(identifier) = &current_identifier {
+                    properties.insert(identifier.clone(), (statement, current_type.clone()));
+                }
             }
         }
 

src/abstract_tree/match.rs

@@ -84,16 +84,15 @@ impl AbstractTree for Match {
             if let (Value::Enum(enum_instance), MatchPattern::EnumPattern(enum_pattern)) =
                 (&matcher_value, pattern)
             {
-                if enum_instance.name() == enum_pattern.name().inner()
+                if enum_instance.name() == enum_pattern.name()
-                    && enum_instance.variant_name() == enum_pattern.variant().inner()
+                    && enum_instance.variant() == enum_pattern.variant()
                 {
                     let statement_context = Context::with_variables_from(context)?;
 
                     if let (Some(identifier), Some(value)) =
                         (enum_pattern.inner_identifier(), enum_instance.value())
                     {
-                        statement_context
+                        statement_context.set_value(identifier.clone(), value.as_ref().clone())?;
-                            .set_value(identifier.inner().clone(), value.as_ref().clone())?;
                     }
 
                     return statement.run(source, &statement_context);

src/abstract_tree/struct_definition.rs

@@ -12,7 +12,7 @@ use crate::{
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
 pub struct StructDefinition {
     name: Identifier,
-    properties: BTreeMap<String, (Option<Statement>, Type)>,
+    properties: BTreeMap<Identifier, (Option<Statement>, Type)>,
 }
 
 impl StructDefinition {
@@ -38,10 +38,7 @@ impl StructDefinition {
             all_properties.set(key.clone(), value);
         }
 
-        Ok(StructInstance::new(
+        Ok(StructInstance::new(self.name.clone(), all_properties))
-            self.name.inner().clone(),
-            all_properties,
-        ))
     }
 }
 
@@ -63,7 +60,7 @@ impl AbstractTree for StructDefinition {
             if child_syntax_node.kind() == "identifier" {
                 if current_statement.is_none() {
                     if let (Some(identifier), Some(r#type)) = (&current_identifier, &current_type) {
-                        properties.insert(identifier.inner().clone(), (None, r#type.clone()));
+                        properties.insert(identifier.clone(), (None, r#type.clone()));
                     }
                 }
 
@@ -91,7 +88,7 @@ impl AbstractTree for StructDefinition {
                     };
 
                     properties.insert(
-                        identifier.inner().clone(),
+                        identifier.clone(),
                         (current_statement.clone(), r#type.clone()),
                     );
                 }
@@ -110,10 +107,7 @@ impl AbstractTree for StructDefinition {
     }
 
     fn run(&self, _source: &str, context: &Context) -> Result<Value, RuntimeError> {
-        context.set_definition(
+        context.set_definition(self.name.clone(), TypeDefinition::Struct(self.clone()))?;
-            self.name.inner().clone(),
-            TypeDefinition::Struct(self.clone()),
-        )?;
 
         Ok(Value::none())
     }

src/abstract_tree/type.rs

@@ -1,11 +1,12 @@
 use std::fmt::{self, Display, Formatter};
 
 use serde::{Deserialize, Serialize};
+use tree_sitter::Node as SyntaxNode;
 
 use crate::{
     built_in_types::BuiltInType,
     error::{RuntimeError, SyntaxError, ValidationError},
-    AbstractTree, Context, Format, Identifier, SyntaxNode, Value,
+    AbstractTree, Context, Format, Identifier, Value,
 };
 
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
@@ -13,10 +14,9 @@ pub enum Type {
     Any,
     Boolean,
     Collection,
-    Custom(Identifier),
+    Custom {
-    CustomWithArgument {
         name: Identifier,
-        argument: Box<Type>,
+        argument: Option<Box<Type>>,
     },
     Float,
     Function {
@@ -33,8 +33,15 @@ pub enum Type {
 }
 
 impl Type {
+    pub fn custom(name: Identifier, argument: Option<Type>) -> Self {
+        Type::Custom {
+            name,
+            argument: argument.map(|r#type| Box::new(r#type)),
+        }
+    }
+
     pub fn option(inner_type: Option<Type>) -> Self {
-        BuiltInType::Option.get(inner_type).clone()
+        BuiltInType::Option(inner_type).get().clone()
     }
 
     pub fn list(item_type: Type) -> Self {
@@ -75,13 +82,12 @@ impl Type {
             | (Type::Integer, Type::Number)
             | (Type::Float, Type::Number)
             | (Type::String, Type::String) => true,
-            (Type::Custom(left), Type::Custom(right)) => left == right,
             (
-                Type::CustomWithArgument {
+                Type::Custom {
                     name: left_name,
                     argument: left_argument,
                 },
-                Type::CustomWithArgument {
+                Type::Custom {
                     name: right_name,
                     argument: right_argument,
                 },
@@ -138,7 +144,7 @@ impl AbstractTree for Type {
     fn from_syntax(
         node: SyntaxNode,
         _source: &str,
-        _context: &Context,
+        context: &Context,
     ) -> Result<Self, SyntaxError> {
         SyntaxError::expect_syntax_node(_source, "type", node)?;
 
@@ -146,23 +152,18 @@ impl AbstractTree for Type {
 
         let r#type = match type_node.kind() {
             "identifier" => {
-                if node.child_count() == 1 {
+                let name = Identifier::from_syntax(type_node, _source, context)?;
-                    Type::Custom(Identifier::from_syntax(type_node, _source, _context)?)
+                let argument = if let Some(child) = node.child(2) {
+                    Some(Type::from_syntax(child, _source, context)?)
                 } else {
-                    let name = Identifier::from_syntax(type_node, _source, _context)?;
+                    None
+                };
 
-                    let argument_node = node.child(2).unwrap();
+                Type::custom(name, argument)
-                    let argument = Type::from_syntax(argument_node, _source, _context)?;
-
-                    Type::CustomWithArgument {
-                        name,
-                        argument: Box::new(argument),
-                    }
-                }
             }
             "[" => {
                 let item_type_node = node.child(1).unwrap();
-                let item_type = Type::from_syntax(item_type_node, _source, _context)?;
+                let item_type = Type::from_syntax(item_type_node, _source, context)?;
 
                 Type::List(Box::new(item_type))
             }
@@ -178,7 +179,7 @@ impl AbstractTree for Type {
                     let child = node.child(index).unwrap();
 
                     if child.is_named() {
-                        let parameter_type = Type::from_syntax(child, _source, _context)?;
+                        let parameter_type = Type::from_syntax(child, _source, context)?;
 
                         parameter_types.push(parameter_type);
                     }
@@ -186,7 +187,7 @@ impl AbstractTree for Type {
 
                 let final_node = node.child(child_count - 1).unwrap();
                 let return_type = if final_node.is_named() {
-                    Type::from_syntax(final_node, _source, _context)?
+                    Type::from_syntax(final_node, _source, context)?
                 } else {
                     Type::option(None)
                 };
@@ -233,8 +234,7 @@ impl Format for Type {
             Type::Any => output.push_str("any"),
             Type::Boolean => output.push_str("bool"),
             Type::Collection => output.push_str("collection"),
-            Type::Custom(_) => todo!(),
+            Type::Custom {
-            Type::CustomWithArgument {
                 name: _,
                 argument: _,
             } => todo!(),
@@ -279,9 +279,12 @@ impl Display for Type {
             Type::Any => write!(f, "any"),
             Type::Boolean => write!(f, "bool"),
             Type::Collection => write!(f, "collection"),
-            Type::Custom(identifier) => write!(f, "{identifier}"),
+            Type::Custom { name, argument } => {
-            Type::CustomWithArgument { name, argument } => {
+                if let Some(argument) = argument {
-                write!(f, "{name}<{argument}>")
+                    write!(f, "{name}<{argument}>")
+                } else {
+                    write!(f, "{name}")
+                }
             }
             Type::Float => write!(f, "float"),
             Type::Function {

src/abstract_tree/value_node.rs

@@ -121,7 +121,7 @@ impl AbstractTree for ValueNode {
         let r#type = match self {
             ValueNode::Boolean(_) => Type::Boolean,
             ValueNode::Float(_) => Type::Float,
-            ValueNode::Function(function) => function.r#type().clone(),
+            ValueNode::Function(function) => function.r#type(),
             ValueNode::Integer(_) => Type::Integer,
             ValueNode::String(_) => Type::String,
             ValueNode::List(expressions) => {
@@ -147,17 +147,20 @@ impl AbstractTree for ValueNode {
             }
             ValueNode::Map(_) => Type::Map,
             ValueNode::Struct { name, .. }  => {
-                Type::Custom(name.clone())
+                Type::Custom { name: name.clone(), argument: None }
             }
             ValueNode::Range(_) => Type::Range,
             ValueNode::Enum { name, variant: _, expression } => {
                 if let Some(expression) = expression {
-                    Type::CustomWithArgument {
+                    Type::Custom {
                         name: name.clone(),
-                        argument: Box::new(expression.expected_type(context)?)
+                        argument: Some(Box::new(expression.expected_type(context)?))
                     }
                 } else {
-                    Type::Custom(name.clone())
+                    Type::Custom{
+                        name: name.clone(),
+                        argument: None,
+                    }
                 }
             },
         };
@@ -204,7 +207,7 @@ impl AbstractTree for ValueNode {
             ValueNode::Map(map_node) => map_node.run(source, context)?,
             ValueNode::Range(range) => Value::Range(range.clone()),
             ValueNode::Struct { name, properties } => {
-                let instance = if let Some(definition) = context.get_definition(name.inner())? {
+                let instance = if let Some(definition) = context.get_definition(name)? {
                     if let TypeDefinition::Struct(struct_definition) = definition {
                         struct_definition.instantiate(properties, source, context)?
                     } else {
@@ -212,7 +215,7 @@ impl AbstractTree for ValueNode {
                     }
                 } else {
                     return Err(RuntimeError::ValidationFailure(
-                        ValidationError::TypeDefinitionNotFound(name.inner().clone())
+                        ValidationError::TypeDefinitionNotFound(name.clone())
                     ));
                 };
 
@@ -225,9 +228,9 @@ impl AbstractTree for ValueNode {
                 } else {
                     Value::none()
                 };
-                let instance = if let Some(definition) = context.get_definition(name.inner())? {
+                let instance = if let Some(definition) = context.get_definition(name)? {
                     if let TypeDefinition::Enum(enum_defintion) = definition {
-                        enum_defintion.instantiate(variant.inner().clone(), Some(value))
+                        enum_defintion.instantiate(variant.clone(), Some(value))
                     } else {
                         return Err(RuntimeError::ValidationFailure(
                             ValidationError::ExpectedEnumDefintion {
@@ -237,7 +240,7 @@ impl AbstractTree for ValueNode {
                     }
                 } else {
                     return Err(RuntimeError::ValidationFailure(
-                        ValidationError::TypeDefinitionNotFound(name.inner().clone())
+                        ValidationError::TypeDefinitionNotFound(name.clone())
                     ));
                 };
 

src/built_in_functions/mod.rs

@@ -19,7 +19,7 @@ pub trait Callable {
         &self,
         arguments: &[Value],
         source: &str,
-        outer_context: &Context,
+        context: &Context,
     ) -> Result<Value, RuntimeError>;
 }
 
@@ -72,7 +72,10 @@ impl Callable for BuiltInFunction {
         match self {
             BuiltInFunction::AssertEqual => Type::function(
                 vec![Type::Any, Type::Any],
-                Type::Custom(Identifier::new("Result")),
+                Type::Custom {
+                    name: Identifier::new("Result"),
+                    argument: None,
+                },
             ),
             BuiltInFunction::Fs(fs_function) => fs_function.r#type(),
             BuiltInFunction::Json(json_function) => json_function.r#type(),
@@ -90,7 +93,7 @@ impl Callable for BuiltInFunction {
         &self,
         arguments: &[Value],
         _source: &str,
-        _outer_context: &Context,
+        context: &Context,
     ) -> Result<Value, RuntimeError> {
         match self {
             BuiltInFunction::AssertEqual => {
@@ -101,26 +104,22 @@ impl Callable for BuiltInFunction {
 
                 let result = if left == right {
                     Value::Enum(EnumInstance::new(
-                        "Result".to_string(),
+                        Identifier::new("Result"),
-                        "Ok".to_string(),
+                        Identifier::new("Ok"),
                         Some(Value::none()),
                     ))
                 } else {
                     Value::Enum(EnumInstance::new(
-                        "Result".to_string(),
+                        Identifier::new("Result"),
-                        "Error".to_string(),
+                        Identifier::new("Error"),
                         Some(Value::none()),
                     ))
                 };
 
                 Ok(result)
             }
-            BuiltInFunction::Fs(fs_function) => {
+            BuiltInFunction::Fs(fs_function) => fs_function.call(arguments, _source, context),
-                fs_function.call(arguments, _source, _outer_context)
+            BuiltInFunction::Json(json_function) => json_function.call(arguments, _source, context),
-            }
-            BuiltInFunction::Json(json_function) => {
-                json_function.call(arguments, _source, _outer_context)
-            }
             BuiltInFunction::Length => {
                 RuntimeError::expect_argument_amount(self.name(), 1, arguments.len())?;
 
@@ -184,7 +183,7 @@ impl Callable for BuiltInFunction {
                 Ok(Value::Integer(random()))
             }
             BuiltInFunction::String(string_function) => {
-                string_function.call(arguments, _source, _outer_context)
+                string_function.call(arguments, _source, context)
             }
         }
     }

src/built_in_functions/str.rs

@@ -1,7 +1,7 @@
 use enum_iterator::Sequence;
 use serde::{Deserialize, Serialize};
 
-use crate::{error::RuntimeError, Context, EnumInstance, List, Type, Value};
+use crate::{error::RuntimeError, Context, EnumInstance, Identifier, List, Type, Value};
 
 use super::Callable;
 
@@ -203,7 +203,7 @@ impl Callable for StrFunction {
         &self,
         arguments: &[Value],
         _source: &str,
-        _outer_context: &Context,
+        context: &Context,
     ) -> Result<Value, RuntimeError> {
         let value = match self {
             StrFunction::AsBytes => {
@@ -238,14 +238,14 @@ impl Callable for StrFunction {
 
                 if let Some(index) = find {
                     Value::Enum(EnumInstance::new(
-                        "Option".to_string(),
+                        Identifier::new("Option"),
-                        "Some".to_string(),
+                        Identifier::new("Some"),
                         Some(index),
                     ))
                 } else {
                     Value::Enum(EnumInstance::new(
-                        "Option".to_string(),
+                        Identifier::new("Option"),
-                        "None".to_string(),
+                        Identifier::new("None"),
                         Some(Value::none()),
                     ))
                 }
@@ -477,8 +477,8 @@ impl Callable for StrFunction {
 
                 if let Some(value) = stripped {
                     Value::Enum(EnumInstance::new(
-                        "Option".to_string(),
+                        Identifier::new("Option"),
-                        "Some".to_string(),
+                        Identifier::new("Some"),
                         Some(value),
                     ))
                 } else {

src/built_in_identifiers.rs

@@ -0,0 +1,29 @@
+use std::sync::OnceLock;
+
+use enum_iterator::{all, Sequence};
+
+use crate::Identifier;
+
+pub fn all_built_in_identifiers() -> impl Iterator<Item = BuiltInIdentifier> {
+    all()
+}
+
+const OPTION: OnceLock<Identifier> = OnceLock::new();
+const NONE: OnceLock<Identifier> = OnceLock::new();
+
+#[derive(Sequence)]
+pub enum BuiltInIdentifier {
+    Option,
+    None,
+}
+
+impl BuiltInIdentifier {
+    pub fn get(&self) -> &Identifier {
+        match self {
+            BuiltInIdentifier::Option => {
+                return OPTION.get_or_init(|| Identifier::new("Option"));
+            }
+            BuiltInIdentifier::None => return NONE.get_or_init(|| Identifier::new("None")),
+        }
+    }
+}

src/built_in_type_definitions.rs

@@ -2,10 +2,13 @@ use std::sync::OnceLock;
 
 use enum_iterator::{all, Sequence};
 
-use crate::{EnumDefinition, Identifier, Type, TypeDefinition, VariantContent};
+use crate::{
+    error::rw_lock_error::RwLockError, Context, EnumDefinition, Identifier, Type, TypeDefinition,
+    VariantContent,
+};
 
-static OPTION: OnceLock<TypeDefinition> = OnceLock::new();
+static OPTION: OnceLock<Result<TypeDefinition, RwLockError>> = OnceLock::new();
-static RESULT: OnceLock<TypeDefinition> = OnceLock::new();
+static RESULT: OnceLock<Result<TypeDefinition, RwLockError>> = OnceLock::new();
 
 pub fn all_built_in_type_definitions() -> impl Iterator<Item = BuiltInTypeDefinition> {
     all()
@@ -25,25 +28,29 @@ impl BuiltInTypeDefinition {
         }
     }
 
-    pub fn get(&self) -> &TypeDefinition {
+    pub fn get(&self, context: &Context) -> &Result<TypeDefinition, RwLockError> {
         match self {
             BuiltInTypeDefinition::Option => OPTION.get_or_init(|| {
-                TypeDefinition::Enum(EnumDefinition::new(
+                let definition = TypeDefinition::Enum(EnumDefinition::new(
                     Identifier::new(self.name()),
                     vec![
                         (Identifier::new("Some"), VariantContent::Type(Type::Any)),
                         (Identifier::new("None"), VariantContent::None),
                     ],
-                ))
+                ));
+
+                Ok(definition)
             }),
             BuiltInTypeDefinition::Result => RESULT.get_or_init(|| {
-                TypeDefinition::Enum(EnumDefinition::new(
+                let definition = TypeDefinition::Enum(EnumDefinition::new(
                     Identifier::new(self.name()),
                     vec![
                         (Identifier::new("Ok"), VariantContent::Type(Type::Any)),
                         (Identifier::new("Err"), VariantContent::Type(Type::Any)),
                     ],
-                ))
+                ));
+
+                Ok(definition)
             }),
         }
     }

src/built_in_types.rs

@@ -1,34 +1,33 @@
 use std::sync::OnceLock;
 
-use enum_iterator::Sequence;
-use serde::{Deserialize, Serialize};
-
 use crate::{Identifier, Type};
 
 static OPTION: OnceLock<Type> = OnceLock::new();
 
-#[derive(Sequence, Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
 pub enum BuiltInType {
-    Option,
+    Option(Option<Type>),
 }
 
 impl BuiltInType {
     pub fn name(&self) -> &'static str {
         match self {
-            BuiltInType::Option => todo!(),
+            BuiltInType::Option(_) => "Option",
         }
     }
 
-    pub fn get(&self, inner_type: Option<Type>) -> &Type {
+    pub fn get(&self) -> &Type {
         match self {
-            BuiltInType::Option => OPTION.get_or_init(|| {
+            BuiltInType::Option(content_type) => OPTION.get_or_init(|| {
-                if let Some(inner_type) = inner_type {
+                if let Some(content_type) = content_type {
-                    Type::CustomWithArgument {
+                    Type::Custom {
                         name: Identifier::new("Option"),
-                        argument: Box::new(inner_type),
+                        argument: Some(Box::new(content_type.clone())),
                     }
                 } else {
-                    Type::Custom(Identifier::new("Option"))
+                    Type::Custom {
+                        name: Identifier::new("Option"),
+                        argument: None,
+                    }
                 }
             }),
         }

src/built_in_values.rs

@@ -1,21 +1,19 @@
-use std::{collections::BTreeMap, env::args, sync::OnceLock};
+use std::{env::args, sync::OnceLock};
 
 use enum_iterator::{all, Sequence};
 use serde::{Deserialize, Serialize};
 
 use crate::{
     built_in_functions::{fs::fs_functions, json::json_functions, str::string_functions, Callable},
-    error::{RuntimeError, SyntaxError, ValidationError},
+    BuiltInFunction, EnumInstance, Function, Identifier, List, Map, Value,
-    AbstractTree, BuiltInFunction, Context, EnumInstance, Format, Function, Identifier, List, Map,
-    SyntaxNode, Type, Value,
 };
 
 static ARGS: OnceLock<Value> = OnceLock::new();
 static FS: OnceLock<Value> = OnceLock::new();
 static JSON: OnceLock<Value> = OnceLock::new();
-static RANDOM: OnceLock<Value> = OnceLock::new();
-static STRING: OnceLock<Value> = OnceLock::new();
 static NONE: OnceLock<Value> = OnceLock::new();
+static RANDOM: OnceLock<Value> = OnceLock::new();
+static STR: OnceLock<Value> = OnceLock::new();
 
 /// Returns the entire built-in value API.
 pub fn all_built_in_values() -> impl Iterator<Item = BuiltInValue> {
@@ -86,23 +84,6 @@ impl BuiltInValue {
         }
     }
 
-    /// Returns the value's type.
-    ///
-    /// This is checked with a unit test to ensure it matches the value.
-    pub fn r#type(&self) -> Type {
-        match self {
-            BuiltInValue::Args => Type::list(Type::String),
-            BuiltInValue::AssertEqual => BuiltInFunction::AssertEqual.r#type(),
-            BuiltInValue::Fs => Type::Map,
-            BuiltInValue::Json => Type::Map,
-            BuiltInValue::Length => BuiltInFunction::Length.r#type(),
-            BuiltInValue::None => Type::Custom(Identifier::new("Option")),
-            BuiltInValue::Output => BuiltInFunction::Output.r#type(),
-            BuiltInValue::Random => Type::Map,
-            BuiltInValue::Str => Type::Map,
-        }
-    }
-
     /// Returns the value by creating it or, if it has already been accessed, retrieving it from its
     /// [OnceLock][].
     pub fn get(&self) -> &Value {
@@ -116,42 +97,40 @@ impl BuiltInValue {
                 &Value::Function(Function::BuiltIn(BuiltInFunction::AssertEqual))
             }
             BuiltInValue::Fs => FS.get_or_init(|| {
-                let mut fs_context = BTreeMap::new();
+                let mut fs_map = Map::new();
 
                 for fs_function in fs_functions() {
-                    let key = fs_function.name().to_string();
+                    let key = fs_function.name();
                     let value =
                         Value::Function(Function::BuiltIn(BuiltInFunction::Fs(fs_function)));
 
-                    fs_context.insert(key, value);
+                    fs_map.set(Identifier::new(key), value);
                 }
 
-                Value::Map(Map::with_values(fs_context))
+                Value::Map(fs_map)
             }),
             BuiltInValue::Json => JSON.get_or_init(|| {
-                let mut json_context = BTreeMap::new();
+                let mut json_map = Map::new();
 
                 for json_function in json_functions() {
-                    let key = json_function.name().to_string();
+                    let key = json_function.name();
                     let value =
                         Value::Function(Function::BuiltIn(BuiltInFunction::Json(json_function)));
 
-                    json_context.insert(key, value);
+                    json_map.set(Identifier::new(key), value);
                 }
 
-                Value::Map(Map::with_values(json_context))
+                Value::Map(json_map)
             }),
             BuiltInValue::Length => &Value::Function(Function::BuiltIn(BuiltInFunction::Length)),
-            BuiltInValue::None => NONE.get_or_init(|| {
+            BuiltInValue::None => &Value::Enum(EnumInstance::new(
-                Value::Enum(EnumInstance::new(
+                Identifier::new("Option"),
-                    "Option".to_string(),
+                Identifier::new("None"),
-                    "None".to_string(),
+                None,
-                    None,
+            )),
-                ))
-            }),
             BuiltInValue::Output => &Value::Function(Function::BuiltIn(BuiltInFunction::Output)),
             BuiltInValue::Random => RANDOM.get_or_init(|| {
-                let mut random_context = BTreeMap::new();
+                let mut random_map = Map::new();
 
                 for built_in_function in [
                     BuiltInFunction::RandomBoolean,
@@ -159,83 +138,28 @@ impl BuiltInValue {
                     BuiltInFunction::RandomFrom,
                     BuiltInFunction::RandomInteger,
                 ] {
-                    let key = built_in_function.name().to_string();
+                    let identifier = Identifier::new(built_in_function.name());
                     let value = Value::Function(Function::BuiltIn(built_in_function));
 
-                    random_context.insert(key, value);
+                    random_map.set(identifier, value);
                 }
 
-                Value::Map(Map::with_values(random_context))
+                Value::Map(random_map)
             }),
-            BuiltInValue::Str => STRING.get_or_init(|| {
+            BuiltInValue::Str => STR.get_or_init(|| {
-                let mut string_context = BTreeMap::new();
+                let mut str_map = Map::new();
 
                 for string_function in string_functions() {
-                    let key = string_function.name().to_string();
+                    let identifier = Identifier::new(string_function.name());
                     let value = Value::Function(Function::BuiltIn(BuiltInFunction::String(
                         string_function,
                     )));
 
-                    string_context.insert(key, value);
+                    str_map.set(identifier, value);
                 }
 
-                Value::Map(Map::with_values(string_context))
+                Value::Map(str_map)
             }),
         }
     }
 }
-
-impl AbstractTree for BuiltInValue {
-    fn from_syntax(
-        node: SyntaxNode,
-        _source: &str,
-        _context: &Context,
-    ) -> Result<Self, SyntaxError> {
-        let built_in_value = match node.kind() {
-            "args" => BuiltInValue::Args,
-            "assert_equal" => BuiltInValue::AssertEqual,
-            "fs" => BuiltInValue::Fs,
-            "json" => BuiltInValue::Json,
-            "length" => BuiltInValue::Length,
-            "output" => BuiltInValue::Output,
-            "random" => BuiltInValue::Random,
-            "str" => BuiltInValue::Str,
-            _ => todo!(),
-        };
-
-        Ok(built_in_value)
-    }
-
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
-        Ok(self.r#type())
-    }
-
-    fn validate(&self, _source: &str, _context: &Context) -> Result<(), ValidationError> {
-        Ok(())
-    }
-
-    fn run(&self, _source: &str, _context: &Context) -> Result<Value, RuntimeError> {
-        Ok(self.get().clone())
-    }
-}
-
-impl Format for BuiltInValue {
-    fn format(&self, output: &mut String, _indent_level: u8) {
-        output.push_str(&self.get().to_string());
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::all_built_in_values;
-
-    #[test]
-    fn check_built_in_types() {
-        for built_in_value in all_built_in_values() {
-            let expected = built_in_value.r#type();
-            let actual = built_in_value.get().r#type();
-
-            assert_eq!(expected, actual);
-        }
-    }
-}

src/context.rs

@@ -35,7 +35,7 @@ use std::{
 
 use crate::{
     built_in_type_definitions::all_built_in_type_definitions, built_in_values::all_built_in_values,
-    error::rw_lock_error::RwLockError, Type, TypeDefinition, Value,
+    error::rw_lock_error::RwLockError, Identifier, Type, TypeDefinition, Value,
 };
 
 /// An execution context that variable and type data during the [Interpreter]'s
@@ -44,7 +44,7 @@ use crate::{
 /// See the [module-level docs][self] for more info.
 #[derive(Clone, Debug)]
 pub struct Context {
-    inner: Arc<RwLock<BTreeMap<String, ValueData>>>,
+    inner: Arc<RwLock<BTreeMap<Identifier, ValueData>>>,
 }
 
 impl Context {
@@ -56,7 +56,7 @@ impl Context {
     }
 
     /// Return a lock guard to the inner BTreeMap.
-    pub fn inner(&self) -> Result<RwLockReadGuard<BTreeMap<String, ValueData>>, RwLockError> {
+    pub fn inner(&self) -> Result<RwLockReadGuard<BTreeMap<Identifier, ValueData>>, RwLockError> {
         Ok(self.inner.read()?)
     }
 
@@ -112,15 +112,15 @@ impl Context {
     ///
     /// This will also return a built-in value if one matches the key. See the
     /// [module-level docs][self] for more info.
-    pub fn get_value(&self, key: &str) -> Result<Option<Value>, RwLockError> {
+    pub fn get_value(&self, identifier: &Identifier) -> Result<Option<Value>, RwLockError> {
-        if let Some(value_data) = self.inner.read()?.get(key) {
+        if let Some(value_data) = self.inner.read()?.get(identifier) {
             if let ValueData::Value { inner, .. } = value_data {
                 return Ok(Some(inner.clone()));
             }
         }
 
         for built_in_value in all_built_in_values() {
-            if key == built_in_value.name() {
+            if built_in_value.name() == identifier.inner().as_ref() {
                 return Ok(Some(built_in_value.get().clone()));
             }
         }
@@ -132,8 +132,8 @@ impl Context {
     ///
     /// If the key matches a stored value, its type will be returned. It if
     /// matches a type hint, the type hint will be returned.
-    pub fn get_type(&self, key: &str) -> Result<Option<Type>, RwLockError> {
+    pub fn get_type(&self, identifier: &Identifier) -> Result<Option<Type>, RwLockError> {
-        if let Some(value_data) = self.inner.read()?.get(key) {
+        if let Some(value_data) = self.inner.read()?.get(identifier) {
             match value_data {
                 ValueData::Value { inner, .. } => return Ok(Some(inner.r#type())),
                 ValueData::TypeHint { inner, .. } => return Ok(Some(inner.clone())),
@@ -141,12 +141,6 @@ impl Context {
             }
         }
 
-        for built_in_value in all_built_in_values() {
-            if key == built_in_value.name() {
-                return Ok(Some(built_in_value.r#type()));
-            }
-        }
-
         Ok(None)
     }
 
@@ -154,16 +148,19 @@ impl Context {
     ///
     /// This will also return a built-in type definition if one matches the key.
     /// See the [module-level docs][self] for more info.
-    pub fn get_definition(&self, key: &str) -> Result<Option<TypeDefinition>, RwLockError> {
+    pub fn get_definition(
-        if let Some(value_data) = self.inner.read()?.get(key) {
+        &self,
+        identifier: &Identifier,
+    ) -> Result<Option<TypeDefinition>, RwLockError> {
+        if let Some(value_data) = self.inner.read()?.get(identifier) {
             if let ValueData::TypeDefinition(definition) = value_data {
                 return Ok(Some(definition.clone()));
             }
         }
 
         for built_in_definition in all_built_in_type_definitions() {
-            if key == built_in_definition.name() {
+            if built_in_definition.name() == identifier.inner().as_ref() {
-                return Ok(Some(built_in_definition.get().clone()));
+                return Ok(Some(built_in_definition.get(self).clone()?));
             }
         }
 
@@ -171,7 +168,7 @@ impl Context {
     }
 
     /// Set a value to a key.
-    pub fn set_value(&self, key: String, value: Value) -> Result<(), RwLockError> {
+    pub fn set_value(&self, key: Identifier, value: Value) -> Result<(), RwLockError> {
         self.inner.write()?.insert(
             key,
             ValueData::Value {
@@ -187,7 +184,7 @@ impl Context {
     ///
     /// This allows the interpreter to check a value's type before the value
     /// actually exists by predicting what the abstract tree will produce.
-    pub fn set_type(&self, key: String, r#type: Type) -> Result<(), RwLockError> {
+    pub fn set_type(&self, key: Identifier, r#type: Type) -> Result<(), RwLockError> {
         self.inner
             .write()?
             .insert(key, ValueData::TypeHint { inner: r#type });
@@ -201,7 +198,7 @@ impl Context {
     /// later while using this context.
     pub fn set_definition(
         &self,
-        key: String,
+        key: Identifier,
         definition: TypeDefinition,
     ) -> Result<(), RwLockError> {
         self.inner
@@ -212,7 +209,7 @@ impl Context {
     }
 
     /// Remove a key-value pair.
-    pub fn unset(&self, key: &str) -> Result<(), RwLockError> {
+    pub fn unset(&self, key: &Identifier) -> Result<(), RwLockError> {
         self.inner.write()?.remove(key);
 
         Ok(())

src/error/runtime_error.rs

@@ -7,7 +7,7 @@ use std::{
     time,
 };
 
-use crate::{Type, Value};
+use crate::{Identifier, Type, Value};
 
 use super::{rw_lock_error::RwLockError, ValidationError};
 
@@ -106,7 +106,7 @@ pub enum RuntimeError {
     Utf8(FromUtf8Error),
 
     /// Failed to find a variable with a value for this key.
-    VariableIdentifierNotFound(String),
+    VariableIdentifierNotFound(Identifier),
 
     /// A built-in function was called with the wrong amount of arguments.
     ExpectedBuiltInFunctionArgumentAmount {

src/error/validation_error.rs

@@ -65,7 +65,7 @@ pub enum ValidationError {
     VariableIdentifierNotFound(Identifier),
 
     /// Failed to find a type definition with this key.
-    TypeDefinitionNotFound(String),
+    TypeDefinitionNotFound(Identifier),
 
     /// Failed to find an enum definition with this key.
     ExpectedEnumDefintion { actual: TypeDefinition },

src/lib.rs

@@ -17,6 +17,7 @@ pub use tree_sitter::Node as SyntaxNode;
 
 pub mod abstract_tree;
 pub mod built_in_functions;
+pub mod built_in_identifiers;
 pub mod built_in_type_definitions;
 pub mod built_in_types;
 pub mod built_in_values;

src/value/enum_instance.rs

@@ -2,30 +2,30 @@ use std::fmt::{self, Display, Formatter};
 
 use serde::{Deserialize, Serialize};
 
-use crate::Value;
+use crate::{Identifier, Value};
 
 #[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
 pub struct EnumInstance {
-    name: String,
+    name: Identifier,
-    variant_name: String,
+    variant: Identifier,
     value: Option<Box<Value>>,
 }
 
 impl EnumInstance {
-    pub fn new(name: String, variant_name: String, value: Option<Value>) -> Self {
+    pub fn new(name: Identifier, variant_name: Identifier, value: Option<Value>) -> Self {
         Self {
             name,
-            variant_name,
+            variant: variant_name,
             value: value.map(|value| Box::new(value)),
         }
     }
 
-    pub fn name(&self) -> &String {
+    pub fn name(&self) -> &Identifier {
         &self.name
     }
 
-    pub fn variant_name(&self) -> &String {
+    pub fn variant(&self) -> &Identifier {
-        &self.variant_name
+        &self.variant
     }
 
     pub fn value(&self) -> &Option<Box<Value>> {
@@ -35,6 +35,6 @@ impl EnumInstance {
 
 impl Display for EnumInstance {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "{}::{}({:?})", self.name, self.variant_name, self.value)
+        write!(f, "{}::{}({:?})", self.name, self.variant, self.value)
     }
 }

src/value/list.rs

@@ -1,8 +1,4 @@
-use std::{
+use std::fmt::{self, Display, Formatter};
-    cmp::Ordering,
-    fmt::{self, Display, Formatter},
-    sync::{Arc, RwLock, RwLockReadGuard, RwLockWriteGuard},
-};
 
 use stanza::{
     renderer::{console::Console, Renderer},
@@ -12,8 +8,8 @@ use stanza::{
 
 use crate::Value;
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord)]
-pub struct List(Arc<RwLock<Vec<Value>>>);
+pub struct List(Vec<Value>);
 
 impl Default for List {
     fn default() -> Self {
@@ -23,23 +19,23 @@ impl Default for List {
 
 impl List {
     pub fn new() -> Self {
-        List(Arc::new(RwLock::new(Vec::new())))
+        List(Vec::new())
     }
 
     pub fn with_capacity(capacity: usize) -> Self {
-        List(Arc::new(RwLock::new(Vec::with_capacity(capacity))))
+        List(Vec::with_capacity(capacity))
     }
 
     pub fn with_items(items: Vec<Value>) -> Self {
-        List(Arc::new(RwLock::new(items)))
+        List(items)
     }
 
-    pub fn items(&self) -> RwLockReadGuard<'_, Vec<Value>> {
+    pub fn items(&self) -> &Vec<Value> {
-        self.0.read().unwrap()
+        &self.0
     }
 
-    pub fn items_mut(&self) -> RwLockWriteGuard<'_, Vec<Value>> {
+    pub fn items_mut(&mut self) -> &mut Vec<Value> {
-        self.0.write().unwrap()
+        &mut self.0
     }
 
     pub fn as_text_table(&self) -> Table {
@@ -73,32 +69,6 @@ impl List {
     }
 }
 
-impl Eq for List {}
-
-impl PartialEq for List {
-    fn eq(&self, other: &Self) -> bool {
-        let left = self.0.read().unwrap().clone().into_iter();
-        let right = other.0.read().unwrap().clone().into_iter();
-
-        left.eq(right)
-    }
-}
-
-impl Ord for List {
-    fn cmp(&self, other: &Self) -> Ordering {
-        let left = self.0.read().unwrap().clone().into_iter();
-        let right = other.0.read().unwrap().clone().into_iter();
-
-        left.cmp(right)
-    }
-}
-
-impl PartialOrd for List {
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
 impl Display for List {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         let renderer = Console::default();

src/value/map.rs

@@ -9,7 +9,7 @@ use std::{
     fmt::{self, Display, Formatter},
 };
 
-use crate::value::Value;
+use crate::{Identifier, Value};
 
 /// A collection dust variables comprised of key-value pairs.
 ///
@@ -17,7 +17,7 @@ use crate::value::Value;
 /// to one another.
 #[derive(Clone, Debug, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Map {
-    inner: BTreeMap<String, Value>,
+    inner: BTreeMap<Identifier, Value>,
 }
 
 impl Map {
@@ -28,19 +28,19 @@ impl Map {
         }
     }
 
-    pub fn with_values(variables: BTreeMap<String, Value>) -> Self {
+    pub fn with_values(variables: BTreeMap<Identifier, Value>) -> Self {
         Map { inner: variables }
     }
 
-    pub fn inner(&self) -> &BTreeMap<String, Value> {
+    pub fn inner(&self) -> &BTreeMap<Identifier, Value> {
         &self.inner
     }
 
-    pub fn get(&self, key: &str) -> Option<&Value> {
+    pub fn get(&self, key: &Identifier) -> Option<&Value> {
         self.inner.get(key)
     }
 
-    pub fn set(&mut self, key: String, value: Value) {
+    pub fn set(&mut self, key: Identifier, value: Value) {
         self.inner.insert(key, value);
     }
 
@@ -63,7 +63,7 @@ impl Map {
                     vec![key.into(), list.as_text_table().into()],
                 ));
             } else {
-                table.push_row([key, &value.to_string()]);
+                table.push_row([key.to_string(), value.to_string()]);
             };
         }
 

src/value/mod.rs

@@ -11,7 +11,6 @@ use serde::{
 
 use std::{
     cmp::Ordering,
-    collections::BTreeMap,
     convert::TryFrom,
     fmt::{self, Display, Formatter},
     marker::PhantomData,
@@ -55,8 +54,8 @@ impl Value {
 
     pub fn some(value: Value) -> Value {
         Value::Enum(EnumInstance::new(
-            "Option".to_string(),
+            Identifier::new("Option"),
-            "Some".to_string(),
+            Identifier::new("Some"),
             Some(value),
         ))
     }
@@ -97,7 +96,7 @@ impl Value {
 
                 for (key, value) in map.inner() {
                     identifier_types.push((
-                        Identifier::new(key.clone()),
+                        Identifier::new(key.inner()),
                         TypeSpecification::new(value.r#type()),
                     ));
                 }
@@ -828,13 +827,15 @@ impl<'de> Visitor<'de> for ValueVisitor {
     where
         M: MapAccess<'de>,
     {
-        let mut map = BTreeMap::new();
+        let mut map = Map::new();
 
         while let Some((key, value)) = access.next_entry::<String, Value>()? {
-            map.insert(key, value);
+            let identifier = Identifier::new(&key);
+
+            map.set(identifier, value);
         }
 
-        Ok(Value::Map(Map::with_values(map)))
+        Ok(Value::Map(map))
     }
 
     fn visit_enum<A>(self, data: A) -> std::result::Result<Self::Value, A::Error>

src/value/struct_instance.rs

@@ -2,16 +2,16 @@ use std::fmt::{self, Display, Formatter};
 
 use serde::{ser::SerializeMap, Serialize, Serializer};
 
-use crate::Map;
+use crate::{Identifier, Map};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct StructInstance {
-    name: String,
+    name: Identifier,
     map: Map,
 }
 
 impl StructInstance {
-    pub fn new(name: String, map: Map) -> Self {
+    pub fn new(name: Identifier, map: Map) -> Self {
         StructInstance { name, map }
     }
 }

tests/value.rs

@@ -138,7 +138,7 @@ fn function() {
     };
 
     assert_eq!(
-        &vec![Identifier::new("x".to_string())],
+        &vec![Identifier::new_or_get("x".to_string())],
         function.parameters()
     );
     assert_eq!(&Type::Boolean, function.return_type());