diff --git a/dust-lang/src/abstract_tree/if_else.rs b/dust-lang/src/abstract_tree/if_else.rs
index a9f4166..449afeb 100644
--- a/dust-lang/src/abstract_tree/if_else.rs
+++ b/dust-lang/src/abstract_tree/if_else.rs
@@ -39,16 +39,16 @@ impl AbstractNode for IfElse {
         self.if_expression.validate(context)?;
         self.if_block.node.validate(context)?;
 
+        let expected_type = self.if_block.node.expected_type(context)?;
         let if_expression_type = self.if_expression.expected_type(context)?;
 
         if let Type::Boolean = if_expression_type {
             if let Some(else_block) = &self.else_block {
                 else_block.node.validate(context)?;
 
-                let expected = self.if_block.node.expected_type(context)?;
                 let actual = else_block.node.expected_type(context)?;
 
-                expected
+                expected_type
                     .check(&actual)
                     .map_err(|conflict| ValidationError::TypeCheck {
                         conflict,
@@ -56,14 +56,37 @@ impl AbstractNode for IfElse {
                         expected_position: self.if_expression.position(),
                     })?;
             }
-
-            Ok(())
         } else {
-            Err(ValidationError::ExpectedBoolean {
+            return Err(ValidationError::ExpectedBoolean {
                 actual: if_expression_type,
                 position: self.if_expression.position(),
-            })
+            });
         }
+
+        for (expression, block) in &self.else_ifs {
+            let expression_type = expression.expected_type(context)?;
+
+            if let Type::Boolean = expression_type {
+                block.node.validate(context)?;
+
+                let actual = block.node.expected_type(context)?;
+
+                expected_type
+                    .check(&actual)
+                    .map_err(|conflict| ValidationError::TypeCheck {
+                        conflict,
+                        actual_position: self.if_block.node.last_statement().position(),
+                        expected_position: self.if_expression.position(),
+                    })?;
+            } else {
+                return Err(ValidationError::ExpectedBoolean {
+                    actual: if_expression_type,
+                    position: self.if_expression.position(),
+                });
+            }
+        }
+
+        Ok(())
     }
 
     fn run(self, context: &Context) -> Result<Action, RuntimeError> {
@@ -80,10 +103,37 @@ impl AbstractNode for IfElse {
         if let ValueInner::Boolean(if_boolean) = value.inner().as_ref() {
             if *if_boolean {
                 self.if_block.node.run(context)
-            } else if let Some(else_statement) = self.else_block {
-                else_statement.node.run(context)
             } else {
-                Ok(Action::None)
+                for (expression, block) in self.else_ifs {
+                    let expression_position = expression.position();
+                    let action = expression.run(context)?;
+                    let value = if let Action::Return(value) = action {
+                        value
+                    } else {
+                        return Err(RuntimeError::ValidationFailure(
+                            ValidationError::InterpreterExpectedReturn(expression_position),
+                        ));
+                    };
+
+                    if let ValueInner::Boolean(else_if_boolean) = value.inner().as_ref() {
+                        if *else_if_boolean {
+                            return block.node.run(context);
+                        }
+                    } else {
+                        return Err(RuntimeError::ValidationFailure(
+                            ValidationError::ExpectedBoolean {
+                                actual: value.r#type(context)?,
+                                position: expression_position,
+                            },
+                        ));
+                    }
+                }
+
+                if let Some(else_statement) = self.else_block {
+                    else_statement.node.run(context)
+                } else {
+                    Ok(Action::None)
+                }
             }
         } else {
             Err(RuntimeError::ValidationFailure(
diff --git a/dust-lang/src/abstract_tree/while.rs b/dust-lang/src/abstract_tree/while.rs
index 8783531..602bc8e 100644
--- a/dust-lang/src/abstract_tree/while.rs
+++ b/dust-lang/src/abstract_tree/while.rs
@@ -40,7 +40,7 @@ impl AbstractNode for While {
     fn run(self, _context: &Context) -> Result<Action, RuntimeError> {
         let get_boolean = || -> Result<Value, RuntimeError> {
             let expression_position = self.expression.position();
-            let action = self.expression.run(_context)?;
+            let action = self.expression.clone().run(_context)?;
 
             if let Action::Return(value) = action {
                 Ok(value)
@@ -51,16 +51,14 @@ impl AbstractNode for While {
             }
         };
 
-        if let ValueInner::Boolean(boolean) = get_boolean()?.inner().as_ref() {
-            while *boolean {
-                for statement in &self.statements {
-                    let action = statement.clone().run(_context)?;
+        while let ValueInner::Boolean(true) = get_boolean()?.inner().as_ref() {
+            for statement in &self.statements {
+                let action = statement.clone().run(_context)?;
 
-                    match action {
-                        Action::Return(_) => {}
-                        Action::None => {}
-                        Action::Break => return Ok(Action::Break),
-                    }
+                match action {
+                    Action::Return(_) => {}
+                    Action::None => {}
+                    Action::Break => return Ok(Action::Break),
                 }
             }
         }
diff --git a/examples/fizzbuzz.ds b/examples/fizzbuzz.ds
index 28211cc..37b4017 100644
--- a/examples/fizzbuzz.ds
+++ b/examples/fizzbuzz.ds
@@ -5,13 +5,13 @@ while count <= 15 {
 	divides_by_5 = count % 5 == 0
 
 	if divides_by_3 && divides_by_5 { 
-		output('fizzbuzz')
+		io.write_line('fizzbuzz')
 	} else if divides_by_3 { 
-		output('fizz')
+		io.write_line('fizz')
 	} else if divides_by_5 {
-		output('buzz')
+		io.write_line('buzz')
 	} else { 
-		output(count)
+		io.write_line(count)
 	}
 	
 	count += 1
diff --git a/std/io.ds b/std/io.ds
index b47d873..953a7b7 100644
--- a/std/io.ds
+++ b/std/io.ds
@@ -3,7 +3,7 @@ io = {
 		__READ_LINE__()
 	}
 
-	write_line = (output: str) none {
+	write_line = (output: any) none {
 		__WRITE_LINE__(output)
 	}
 }