Add scope and basic stdlib for evaluation

Introduces a `Scope` struct for dynamic scope management and a `Context`
struct to hold the current scope.
Implements a basic standard library with arithmetic operations and a
greater-than comparison.
Modifies `Node::eval` to handle identifiers by resolving them within the
current scope and `Call` nodes for function execution.
Updates the parser to use `Context::new()` for evaluating vector
elements, ensuring a fresh scope.
Enhances the main loop to handle potential runtime errors during
evaluation.

src/ast/nodes.rs

@@ -1,4 +1,5 @@
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
+use std::collections::HashMap;
 use std::fmt::Debug;
 use crate::ast::types::{Identity, Value};
 
@@ -11,15 +12,111 @@ pub struct Node<K> {
 
 /// The base for custom node types (extensions)
 pub trait CustomNode: Debug + Send + Sync {
-    fn eval(&self, node: &Node<UntypedKind>, ctx: &mut Context) -> Value;
+    fn eval(&self, node: &Node<UntypedKind>, ctx: &mut Context) -> Result<Value, String>;
     fn display_name(&self) -> &'static str;
 }
 
+/// Dynamic Scope for the interpreter (Temporary solution)
+#[derive(Debug, Clone)]
+pub struct Scope {
+    values: HashMap<String, Value>,
+    parent: Option<Arc<Mutex<Scope>>>,
+}
+
+impl Scope {
+    pub fn new(parent: Option<Arc<Mutex<Scope>>>) -> Self {
+        Self {
+            values: HashMap::new(),
+            parent,
+        }
+    }
+
+    pub fn define(&mut self, name: &str, value: Value) {
+        self.values.insert(name.to_string(), value);
+    }
+
+    pub fn resolve(&self, name: &str) -> Option<Value> {
+        if let Some(val) = self.values.get(name) {
+            return Some(val.clone());
+        }
+        if let Some(parent) = &self.parent {
+            return parent.lock().unwrap().resolve(name);
+        }
+        None
+    }
+}
+
 /// Evaluation Context (Scope management)
 pub struct Context {
-    // Add variables, scope management here later
+    pub scope: Arc<Mutex<Scope>>,
 }
 
+impl Context {
+    pub fn new() -> Self {
+        let mut root_scope = Scope::new(None);
+        
+        // Register standard library (built-ins)
+        register_stdlib(&mut root_scope);
+
+        Self {
+            scope: Arc::new(Mutex::new(root_scope)),
+        }
+    }
+}
+
+fn register_stdlib(scope: &mut Scope) {
+    // Helper macro to reduce boilerplate
+    macro_rules! bin_op {
+        ($name:expr, $op:tt) => {
+            scope.define($name, Value::Function(Arc::new(|args| {
+                if args.len() < 2 { return Value::Void; } // Error handling later
+                
+                // Fold allow multi-arg: (+ 1 2 3) -> 6
+                let mut acc = match &args[0] {
+                    Value::Int(i) => *i as f64,
+                    Value::Float(f) => *f,
+                    _ => return Value::Void,
+                };
+
+                for arg in &args[1..] {
+                    let val = match arg {
+                        Value::Int(i) => *i as f64,
+                        Value::Float(f) => *f,
+                        _ => return Value::Void,
+                    };
+                    acc = acc $op val;
+                }
+
+                // Return Int if result is integer-like (simplified)
+                if acc.fract() == 0.0 {
+                    Value::Int(acc as i64)
+                } else {
+                    Value::Float(acc)
+                }
+            })));
+        };
+    }
+
+    bin_op!("+", +);
+    bin_op!("-", -);
+    bin_op!("*", *);
+    bin_op!("/", /);
+
+    // Logic
+    scope.define(">", Value::Function(Arc::new(|args| {
+        if args.len() != 2 { return Value::Void; }
+        let (v1, v2) = (&args[0], &args[1]);
+        match (v1, v2) {
+            (Value::Int(a), Value::Int(b)) => Value::Bool(a > b),
+            (Value::Float(a), Value::Float(b)) => Value::Bool(a > b),
+            (Value::Int(a), Value::Float(b)) => Value::Bool((*a as f64) > *b),
+            (Value::Float(a), Value::Int(b)) => Value::Bool(*a > (*b as f64)),
+            _ => Value::Bool(false),
+        }
+    })));
+}
+
+
 /// The core AST variant enum for performance and structure
 #[derive(Debug)]
 pub enum UntypedKind {
@@ -41,25 +138,43 @@ pub enum UntypedKind {
 }
 
 impl Node<UntypedKind> {
-    pub fn eval(&self, ctx: &mut Context) -> Value {
+    pub fn eval(&self, ctx: &mut Context) -> Result<Value, String> {
         match &self.kind {
-            UntypedKind::Nop => Value::Void,
-            UntypedKind::Constant(v) => v.clone(),
-            UntypedKind::Identifier(_) => todo!("Lookup in Context"),
+            UntypedKind::Nop => Ok(Value::Void),
+            UntypedKind::Constant(v) => Ok(v.clone()),
+            
+            UntypedKind::Identifier(name) => {
+                let scope = ctx.scope.lock().unwrap();
+                scope.resolve(name)
+                    .ok_or_else(|| format!("Undefined variable: '{}'", name))
+            },
+
             UntypedKind::If { cond, then_br, else_br } => {
-                if cond.eval(ctx).is_truthy() {
+                let cond_val = cond.eval(ctx)?;
+                if cond_val.is_truthy() {
                     then_br.eval(ctx)
                 } else if let Some(eb) = else_br {
                     eb.eval(ctx)
                 } else {
-                    Value::Void
+                    Ok(Value::Void)
                 }
             }
+            
             UntypedKind::Call { callee, args } => {
-                let _func = callee.eval(ctx);
-                let _eval_args: Vec<Value> = args.iter().map(|a| a.eval(ctx)).collect();
-                todo!("Execute func with args")
+                let func_val = callee.eval(ctx)?;
+                
+                // Evaluate all arguments first (strict evaluation)
+                let mut eval_args = Vec::with_capacity(args.len());
+                for arg in args {
+                    eval_args.push(arg.eval(ctx)?);
+                }
+
+                match func_val {
+                    Value::Function(f) => Ok(f(eval_args)),
+                    _ => Err(format!("Attempt to call a non-function value: {}", func_val)),
+                }
             }
+            
             UntypedKind::Extension(ext) => ext.eval(self, ctx),
         }
     }

src/ast/parser.rs

@@ -122,7 +122,11 @@ impl<'a> Parser<'a> {
         while *self.peek() != TokenKind::RightBracket && *self.peek() != TokenKind::EOF {
             // Vector elements in Myc are usually just constants in a list
             let expr = self.parse_expression()?;
-            elements.push(expr.eval(&mut crate::ast::nodes::Context {})); // Simple direct eval for literals
+            // Simple direct eval for literals (Context::new creates fresh scope)
+            match expr.eval(&mut crate::ast::nodes::Context::new()) {
+                Ok(val) => elements.push(val),
+                Err(e) => return Err(format!("Error evaluating vector element: {}", e)),
+            }
         }
         
         self.expect(TokenKind::RightBracket)?;

src/main.rs

@@ -53,13 +53,19 @@ impl eframe::App for CompilerApp {
 
                     match parser.parse_expression() {
                         Ok(ast) => {
-                            let mut context = Context {};
-                            let result = ast.eval(&mut context);
-                            self.output_log = format!(
-                                "AST Parsed Successfully.\nResult: {}\n\nFinished at {:?}",
-                                result,
-                                std::time::SystemTime::now(),
-                            );
+                            let mut context = Context::new(); // Use new() which registers stdlib
+                            match ast.eval(&mut context) {
+                                Ok(result) => {
+                                    self.output_log = format!(
+                                        "AST Parsed & Evaluated Successfully.\nResult: {}\n\nFinished at {:?}",
+                                        result,
+                                        std::time::SystemTime::now(),
+                                    );
+                                }
+                                Err(e) => {
+                                    self.output_log = format!("Runtime Error: {}", e);
+                                }
+                            }
                         }
                         Err(e) => {
                             self.output_log = format!("Parser Error: {}", e);