diff --git a/src/abstract_tree/assignment.rs b/src/abstract_tree/assignment.rs
index f246538..b901316 100644
--- a/src/abstract_tree/assignment.rs
+++ b/src/abstract_tree/assignment.rs
@@ -4,7 +4,7 @@ use crate::{
     Context, Value,
 };
 
-use super::{AbstractTree, Action, Identifier, Statement, Type, WithPosition};
+use super::{AbstractNode, Action, Identifier, Statement, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Assignment {
@@ -37,7 +37,7 @@ impl Assignment {
     }
 }
 
-impl AbstractTree for Assignment {
+impl AbstractNode for Assignment {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
diff --git a/src/abstract_tree/block.rs b/src/abstract_tree/block.rs
index 1c855e3..43331f0 100644
--- a/src/abstract_tree/block.rs
+++ b/src/abstract_tree/block.rs
@@ -3,7 +3,7 @@ use crate::{
     error::{RuntimeError, ValidationError},
 };
 
-use super::{AbstractTree, Action, Statement, Type, WithPosition};
+use super::{AbstractNode, Action, Statement, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Block {
@@ -20,7 +20,7 @@ impl Block {
     }
 }
 
-impl AbstractTree for Block {
+impl AbstractNode for Block {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         if let Some(statement) = self.statements.last() {
             statement.node.expected_type(_context)
diff --git a/src/abstract_tree/expression.rs b/src/abstract_tree/expression.rs
index fb66486..fe74c47 100644
--- a/src/abstract_tree/expression.rs
+++ b/src/abstract_tree/expression.rs
@@ -4,7 +4,7 @@ use crate::{
 };
 
 use super::{
-    AbstractTree, Action, FunctionCall, Identifier, ListIndex, Logic, MapIndex, Math, Type,
+    AbstractNode, Action, FunctionCall, Identifier, ListIndex, Logic, MapIndex, Math, Type,
     ValueNode,
 };
 
@@ -19,7 +19,7 @@ pub enum Expression {
     Value(ValueNode),
 }
 
-impl AbstractTree for Expression {
+impl AbstractNode for Expression {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         match self {
             Expression::FunctionCall(function_call) => function_call.expected_type(_context),
diff --git a/src/abstract_tree/function_call.rs b/src/abstract_tree/function_call.rs
index 793da23..8cce27f 100644
--- a/src/abstract_tree/function_call.rs
+++ b/src/abstract_tree/function_call.rs
@@ -4,7 +4,7 @@ use crate::{
     value::ValueInner,
 };
 
-use super::{AbstractTree, Action, Expression, Type, WithPosition};
+use super::{AbstractNode, Action, Expression, Type, WithPosition};
 
 #[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord)]
 pub struct FunctionCall {
@@ -24,7 +24,7 @@ impl FunctionCall {
     }
 }
 
-impl AbstractTree for FunctionCall {
+impl AbstractNode for FunctionCall {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         let function_node_type = self.function.node.expected_type(_context)?;
 
diff --git a/src/abstract_tree/identifier.rs b/src/abstract_tree/identifier.rs
index aaaa9be..7bf4496 100644
--- a/src/abstract_tree/identifier.rs
+++ b/src/abstract_tree/identifier.rs
@@ -8,7 +8,7 @@ use crate::{
     error::{RuntimeError, ValidationError},
 };
 
-use super::{AbstractTree, Action, Type};
+use super::{AbstractNode, Action, Type};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Identifier(Arc<String>);
@@ -23,7 +23,7 @@ impl Identifier {
     }
 }
 
-impl AbstractTree for Identifier {
+impl AbstractNode for Identifier {
     fn expected_type(&self, context: &Context) -> Result<Type, ValidationError> {
         if let Some(r#type) = context.get_type(self)? {
             Ok(r#type)
diff --git a/src/abstract_tree/if_else.rs b/src/abstract_tree/if_else.rs
index cf2790e..901ce79 100644
--- a/src/abstract_tree/if_else.rs
+++ b/src/abstract_tree/if_else.rs
@@ -4,7 +4,7 @@ use crate::{
     value::ValueInner,
 };
 
-use super::{AbstractTree, Action, Block, Expression, Type, WithPosition};
+use super::{AbstractNode, Action, Block, Expression, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct IfElse {
@@ -27,7 +27,7 @@ impl IfElse {
     }
 }
 
-impl AbstractTree for IfElse {
+impl AbstractNode for IfElse {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         self.if_block.expected_type(_context)
     }
diff --git a/src/abstract_tree/list_index.rs b/src/abstract_tree/list_index.rs
index 3ad35ed..baf9a33 100644
--- a/src/abstract_tree/list_index.rs
+++ b/src/abstract_tree/list_index.rs
@@ -3,7 +3,7 @@ use crate::{
     error::{RuntimeError, ValidationError},
 };
 
-use super::{AbstractTree, Action, Expression, Type, ValueNode, WithPosition};
+use super::{AbstractNode, Action, Expression, Type, ValueNode, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct ListIndex {
@@ -17,7 +17,7 @@ impl ListIndex {
     }
 }
 
-impl AbstractTree for ListIndex {
+impl AbstractNode for ListIndex {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         let left_type = self.left.node.expected_type(_context)?;
 
diff --git a/src/abstract_tree/logic.rs b/src/abstract_tree/logic.rs
index 2cd7d08..58a4063 100644
--- a/src/abstract_tree/logic.rs
+++ b/src/abstract_tree/logic.rs
@@ -5,7 +5,7 @@ use crate::{
     Value,
 };
 
-use super::{AbstractTree, Action, Expression, Type, WithPosition};
+use super::{AbstractNode, Action, Expression, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub enum Logic {
@@ -20,7 +20,7 @@ pub enum Logic {
     Not(WithPosition<Expression>),
 }
 
-impl AbstractTree for Logic {
+impl AbstractNode for Logic {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         Ok(Type::Boolean)
     }
diff --git a/src/abstract_tree/loop.rs b/src/abstract_tree/loop.rs
index 605727c..7065dea 100644
--- a/src/abstract_tree/loop.rs
+++ b/src/abstract_tree/loop.rs
@@ -5,7 +5,7 @@ use crate::{
     error::{RuntimeError, ValidationError},
 };
 
-use super::{AbstractTree, Action, Statement, Type, WithPosition};
+use super::{AbstractNode, Action, Statement, Type, WithPosition};
 
 #[derive(Clone, Debug)]
 pub struct Loop {
@@ -18,7 +18,7 @@ impl Loop {
     }
 }
 
-impl AbstractTree for Loop {
+impl AbstractNode for Loop {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
diff --git a/src/abstract_tree/map_index.rs b/src/abstract_tree/map_index.rs
index d966fd8..80c0845 100644
--- a/src/abstract_tree/map_index.rs
+++ b/src/abstract_tree/map_index.rs
@@ -4,7 +4,7 @@ use crate::{
     value::ValueInner,
 };
 
-use super::{AbstractTree, Action, Expression, Type, ValueNode, WithPosition};
+use super::{AbstractNode, Action, Expression, Type, ValueNode, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct MapIndex {
@@ -18,7 +18,7 @@ impl MapIndex {
     }
 }
 
-impl AbstractTree for MapIndex {
+impl AbstractNode for MapIndex {
     fn expected_type(&self, context: &Context) -> Result<Type, ValidationError> {
         let left_type = self.left.node.expected_type(context)?;
 
diff --git a/src/abstract_tree/math.rs b/src/abstract_tree/math.rs
index 6725b14..506f6b5 100644
--- a/src/abstract_tree/math.rs
+++ b/src/abstract_tree/math.rs
@@ -5,7 +5,7 @@ use crate::{
     Value,
 };
 
-use super::{AbstractTree, Action, Expression, SourcePosition, Type, WithPosition};
+use super::{AbstractNode, Action, Expression, SourcePosition, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub enum Math {
@@ -16,7 +16,7 @@ pub enum Math {
     Modulo(WithPosition<Expression>, WithPosition<Expression>),
 }
 
-impl AbstractTree for Math {
+impl AbstractNode for Math {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         match self {
             Math::Add(left, _)
diff --git a/src/abstract_tree/mod.rs b/src/abstract_tree/mod.rs
index 8967932..bf884f8 100644
--- a/src/abstract_tree/mod.rs
+++ b/src/abstract_tree/mod.rs
@@ -15,6 +15,8 @@ pub mod r#type;
 pub mod value_node;
 pub mod r#while;
 
+use std::ops::Index;
+
 use chumsky::span::{SimpleSpan, Span};
 
 pub use self::{
@@ -38,7 +40,7 @@ pub use self::{
 
 use crate::{
     context::Context,
-    error::{RuntimeError, ValidationError},
+    error::{Error, RuntimeError, ValidationError},
     Value,
 };
 
@@ -63,7 +65,94 @@ impl From<(usize, usize)> for SourcePosition {
     }
 }
 
-pub trait AbstractTree: Sized {
+#[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord)]
+pub enum Action {
+    Return(Value),
+    Break,
+    None,
+}
+
+pub struct AbstractTree(Vec<WithPosition<Statement>>);
+
+impl AbstractTree {
+    pub fn new(statements: Vec<WithPosition<Statement>>) -> Self {
+        AbstractTree(statements)
+    }
+
+    pub fn run(self, context: &Context) -> Result<Option<Value>, Vec<Error>> {
+        let mut valid_statements = Vec::with_capacity(self.0.len());
+        let mut errors = Vec::new();
+
+        for statement in self.0 {
+            let validation = statement.node.validate(context);
+
+            if let Statement::StructureDefinition(_) = statement.node {
+                match validation {
+                    Ok(_) => {
+                        let run_result = statement.node.run(context);
+
+                        match run_result {
+                            Ok(_) => {}
+                            Err(runtime_error) => {
+                                return Err(vec![Error::Runtime {
+                                    error: runtime_error,
+                                    position: statement.position,
+                                }]);
+                            }
+                        }
+                    }
+                    Err(validation_error) => errors.push(Error::Validation {
+                        error: validation_error,
+                        position: statement.position,
+                    }),
+                }
+            } else {
+                match validation {
+                    Ok(_) => valid_statements.push(statement),
+                    Err(validation_error) => errors.push(Error::Validation {
+                        error: validation_error,
+                        position: statement.position,
+                    }),
+                }
+            }
+        }
+
+        if !errors.is_empty() {
+            return Err(errors);
+        }
+
+        let mut previous = None;
+
+        for statement in valid_statements {
+            let run_result = statement.node.run(context);
+
+            match run_result {
+                Ok(action) => match action {
+                    Action::Return(value) => previous = Some(value),
+                    _ => {}
+                },
+                Err(runtime_error) => {
+                    return Err(vec![Error::Runtime {
+                        error: runtime_error,
+                        position: statement.position,
+                    }]);
+                }
+            }
+        }
+
+        Ok(previous)
+    }
+}
+
+impl Index<usize> for AbstractTree {
+    type Output = WithPosition<Statement>;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.0[index]
+    }
+}
+
+pub trait AbstractNode: Sized {
     fn expected_type(&self, context: &Context) -> Result<Type, ValidationError>;
     fn validate(&self, context: &Context) -> Result<(), ValidationError>;
     fn run(self, context: &Context) -> Result<Action, RuntimeError>;
@@ -75,10 +164,3 @@ pub trait AbstractTree: Sized {
         }
     }
 }
-
-#[derive(Debug, Clone, Eq, PartialEq, PartialOrd, Ord)]
-pub enum Action {
-    Return(Value),
-    Break,
-    None,
-}
diff --git a/src/abstract_tree/statement.rs b/src/abstract_tree/statement.rs
index b42695e..b141d28 100644
--- a/src/abstract_tree/statement.rs
+++ b/src/abstract_tree/statement.rs
@@ -4,7 +4,7 @@ use crate::{
 };
 
 use super::{
-    AbstractTree, Action, Assignment, Block, Expression, IfElse, Loop, StructureDefinition, Type,
+    AbstractNode, Action, Assignment, Block, Expression, IfElse, Loop, StructureDefinition, Type,
     While,
 };
 
@@ -20,7 +20,16 @@ pub enum Statement {
     While(While),
 }
 
-impl AbstractTree for Statement {
+impl Statement {
+    pub fn kind(&self) -> u8 {
+        match self {
+            Statement::StructureDefinition(_) => 0,
+            _ => 1,
+        }
+    }
+}
+
+impl AbstractNode for Statement {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         match self {
             Statement::Assignment(assignment) => assignment.expected_type(_context),
diff --git a/src/abstract_tree/structure_definition.rs b/src/abstract_tree/structure_definition.rs
index ab7090b..0fc9947 100644
--- a/src/abstract_tree/structure_definition.rs
+++ b/src/abstract_tree/structure_definition.rs
@@ -3,7 +3,7 @@ use crate::{
     error::{RuntimeError, ValidationError},
 };
 
-use super::{AbstractTree, Action, Identifier, Type, WithPosition};
+use super::{AbstractNode, Action, Identifier, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct StructureDefinition {
@@ -17,14 +17,12 @@ impl StructureDefinition {
     }
 }
 
-impl AbstractTree for StructureDefinition {
+impl AbstractNode for StructureDefinition {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
 
-    fn validate(&self, context: &Context) -> Result<(), ValidationError> {
-        context.set_type(self.name.clone(), Type::Named(self.name.clone()))?;
-
+    fn validate(&self, _context: &Context) -> Result<(), ValidationError> {
         Ok(())
     }
 
diff --git a/src/abstract_tree/type.rs b/src/abstract_tree/type.rs
index 93241b0..c1669e2 100644
--- a/src/abstract_tree/type.rs
+++ b/src/abstract_tree/type.rs
@@ -6,7 +6,7 @@ use crate::{
     error::{RuntimeError, TypeConflict, ValidationError},
 };
 
-use super::{AbstractTree, Action, WithPosition};
+use super::{AbstractNode, Action, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub enum Type {
@@ -88,7 +88,7 @@ impl Type {
     }
 }
 
-impl AbstractTree for Type {
+impl AbstractNode for Type {
     fn expected_type(&self, _: &Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
diff --git a/src/abstract_tree/value_node.rs b/src/abstract_tree/value_node.rs
index 8567d9e..9efa603 100644
--- a/src/abstract_tree/value_node.rs
+++ b/src/abstract_tree/value_node.rs
@@ -6,7 +6,7 @@ use crate::{
     Value,
 };
 
-use super::{AbstractTree, Action, Block, Expression, Identifier, Type, WithPosition};
+use super::{AbstractNode, Action, Block, Expression, Identifier, Type, WithPosition};
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum ValueNode {
@@ -34,7 +34,7 @@ pub enum ValueNode {
     },
 }
 
-impl AbstractTree for ValueNode {
+impl AbstractNode for ValueNode {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         let r#type = match self {
             ValueNode::Boolean(_) => Type::Boolean,
diff --git a/src/abstract_tree/while.rs b/src/abstract_tree/while.rs
index 14dbc09..2e68e68 100644
--- a/src/abstract_tree/while.rs
+++ b/src/abstract_tree/while.rs
@@ -5,7 +5,7 @@ use crate::{
     Value,
 };
 
-use super::{AbstractTree, Action, Expression, Statement, Type, WithPosition};
+use super::{AbstractNode, Action, Expression, Statement, Type, WithPosition};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct While {
@@ -25,7 +25,7 @@ impl While {
     }
 }
 
-impl AbstractTree for While {
+impl AbstractNode for While {
     fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
diff --git a/src/context.rs b/src/context.rs
index bf8c37f..f41abf5 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -32,10 +32,8 @@ impl Context {
         let mut self_data = self.inner.write()?;
 
         for (identifier, value_data) in other.inner.read()?.iter() {
-            if let ValueData::Type(r#type) = value_data {
-                if let Type::Function { .. } = r#type {
-                    self_data.insert(identifier.clone(), value_data.clone());
-                }
+            if let ValueData::Type(Type::Function { .. }) = value_data {
+                self_data.insert(identifier.clone(), value_data.clone());
             }
         }
 
diff --git a/src/lib.rs b/src/lib.rs
index cb395c8..01b346a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,7 +5,6 @@ pub mod lexer;
 pub mod parser;
 pub mod value;
 
-use abstract_tree::{AbstractTree, Action, WithPosition};
 use context::Context;
 use error::Error;
 use lexer::lex;
@@ -30,41 +29,9 @@ impl Interpreter {
 
     pub fn run(&mut self, source: &str) -> Result<Option<Value>, Vec<Error>> {
         let tokens = lex(source)?;
-        let statements = parse(&tokens)?;
-        let errors = statements
-            .iter()
-            .filter_map(|WithPosition { node, position }| {
-                node.validate(&self.context)
-                    .err()
-                    .map(|error| Error::Validation {
-                        error,
-                        position: position.clone(),
-                    })
-            })
-            .collect::<Vec<Error>>();
+        let abstract_tree = parse(&tokens)?;
+        let value_option = abstract_tree.run(&self.context)?;
 
-        if !errors.is_empty() {
-            return Err(errors);
-        }
-
-        let mut value = None;
-
-        for statement in statements {
-            value = match statement.node.run(&self.context) {
-                Ok(action) => match action {
-                    Action::Break => None,
-                    Action::Return(value) => Some(value),
-                    Action::None => continue,
-                },
-                Err(runtime_error) => {
-                    return Err(vec![Error::Runtime {
-                        error: runtime_error,
-                        position: statement.position,
-                    }])
-                }
-            }
-        }
-
-        Ok(value)
+        Ok(value_option)
     }
 }
diff --git a/src/parser.rs b/src/parser.rs
index d0a8be7..a00b094 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -11,13 +11,18 @@ use crate::{
 pub type ParserInput<'src> =
     SpannedInput<Token<'src>, SimpleSpan, &'src [(Token<'src>, SimpleSpan)]>;
 
-pub fn parse<'src>(
-    tokens: &'src [(Token<'src>, SimpleSpan)],
-) -> Result<Vec<WithPosition<Statement>>, Vec<Error>> {
-    parser()
+pub fn parse<'src>(tokens: &'src [(Token<'src>, SimpleSpan)]) -> Result<AbstractTree, Vec<Error>> {
+    let statements = parser()
         .parse(tokens.spanned((tokens.len()..tokens.len()).into()))
         .into_result()
-        .map_err(|errors| errors.into_iter().map(|error| error.into()).collect())
+        .map_err(|errors| {
+            errors
+                .into_iter()
+                .map(|error| Error::from(error))
+                .collect::<Vec<Error>>()
+        })?;
+
+    Ok(AbstractTree::new(statements))
 }
 
 pub fn parser<'src>() -> impl Parser<
diff --git a/src/value.rs b/src/value.rs
index c2fc434..f82b933 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -15,7 +15,7 @@ use stanza::{
 };
 
 use crate::{
-    abstract_tree::{AbstractTree, Action, Block, Identifier, Type, WithPosition},
+    abstract_tree::{AbstractNode, Action, Block, Identifier, Type, WithPosition},
     context::Context,
     error::{RuntimeError, ValidationError},
 };
diff --git a/tests/variables.rs b/tests/variables.rs
index 78fc7cc..5bd2cd6 100644
--- a/tests/variables.rs
+++ b/tests/variables.rs
@@ -1,5 +1,5 @@
 use dust_lang::{
-    abstract_tree::{AbstractTree, Block, Expression, Identifier, Statement, Type},
+    abstract_tree::{AbstractNode, Block, Expression, Identifier, Statement, Type},
     error::{Error, TypeConflict, ValidationError},
     *,
 };