Clean up; Add error for assignment without a value

dust-lang/src/abstract_tree/assignment.rs

@@ -7,7 +7,9 @@ use crate::{
     Context, Value,
 };
 
-use super::{AbstractNode, Evaluation, ExpectedType, Statement, TypeConstructor, WithPosition};
+use super::{
+    AbstractNode, Evaluation, ExpectedType, Statement, Type, TypeConstructor, WithPosition,
+};
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
 pub struct Assignment {
@@ -44,6 +46,12 @@ impl AbstractNode for Assignment {
     fn validate(&self, context: &mut Context, manage_memory: bool) -> Result<(), ValidationError> {
         let statement_type = self.statement.expected_type(context)?;
 
+        if let Type::None = statement_type {
+            return Err(ValidationError::CannotAssignToNone(
+                self.statement.position(),
+            ));
+        }
+
         if let Some(constructor) = &self.constructor {
             let r#type = constructor.clone().construct(&context)?;
 

dust-lang/src/abstract_tree/mod.rs

@@ -139,13 +139,13 @@ impl AbstractTree {
     fn validate(
         self,
         context: &mut Context,
-        add_variable_uses: bool,
+        manage_memory: bool,
     ) -> Result<Vec<Statement>, Vec<Error>> {
         let mut errors = Vec::new();
         let mut valid_statements = Vec::new();
 
         for statement in self.0 {
-            let validation = statement.validate(context, add_variable_uses);
+            let validation = statement.validate(context, manage_memory);
 
             if let Err(validation_error) = validation {
                 errors.push(Error::Validation {

dust-lang/src/abstract_tree/value_node.rs

@@ -64,7 +64,7 @@ impl AbstractNode for ValueNode {
             body,
         } = self
         {
-            let mut function_context = Context::new(Some(&context));
+            let mut function_context = context.create_child();
 
             if let Some(type_parameters) = type_parameters {
                 for identifier in type_parameters {

dust-lang/src/error.rs

@@ -103,6 +103,7 @@ impl PartialEq for RuntimeError {
 
 #[derive(Debug, PartialEq)]
 pub enum ValidationError {
+    CannotAssignToNone(SourcePosition),
     CannotIndex {
         r#type: Type,
         position: SourcePosition,

dust-lang/src/lib.rs

@@ -150,7 +150,6 @@ impl<'a> Interpreter<'a> {
                     Ok(tokens) => tokens,
                     Err(error) => return Some(error),
                 };
-
                 let parse_result = parser(true)
                     .parse(tokens.spanned((tokens.len()..tokens.len()).into()))
                     .into_result()
@@ -293,6 +292,15 @@ impl InterpreterError {
 
             if let Some(validation_error) = validation_error {
                 match validation_error {
+
+                    ValidationError::CannotAssignToNone(postion) => {
+                        builder.add_label(
+                            Label::new((self.source_id.clone(), postion.0..postion.1))
+                                .with_message(format!(
+                                    "This statement does not yield a value, you cannot assign a variable to it."
+                                )),
+                        );
+                    }
                     ValidationError::ExpectedBoolean { actual, position } => {
                         builder.add_label(
                             Label::new((self.source_id.clone(), position.0..position.1))