diff --git a/compiler/src/backend/dsa/codegen.rs b/compiler/src/backend/dsa/codegen.rs
index e6a4dca..680f9ad 100644
--- a/compiler/src/backend/dsa/codegen.rs
+++ b/compiler/src/backend/dsa/codegen.rs
@@ -5,11 +5,12 @@ use std::time::SystemTime;
 use chrono::{DateTime, Local};
 
 use super::registers::RegisterAllocator;
+use crate::backend::dsa::registers::Register;
 use crate::{block, comment, dsa};
 
 use crate::model::{
-    BinaryOperator, CompilerError, ConstExpr, Declaration, Dependency, Expression,
-    Program, Statement, UnaryOperator, Variable,
+    BinaryOperator, Call, CompilerError, ConstExpr, Declaration, Dependency, Expression,
+    Program, Statement, TypeId, UnaryOperator, Variable,
 };
 
 pub struct CodeGenerator {
@@ -149,9 +150,14 @@ impl CodeGenerator {
                 self.generate_global(&var.name, init)
             }
             Declaration::Function {
-                name, params, body, ..
+                name,
+                params,
+                body,
+                return_type,
             } => {
-                let func = self.generate_function(&name, &params, &body).join("\n");
+                let func = self
+                    .generate_function(&name, &params, &body, return_type)
+                    .join("\n");
 
                 self.functions.push(format!("{func}\n"));
             }
@@ -169,12 +175,23 @@ impl CodeGenerator {
         name: &str,
         params: &[Variable],
         body: &[Statement],
+        return_type: TypeId,
     ) -> Vec<String> {
         let mut code = Vec::new();
 
         // Reset allocator for new function
         self.allocator.reset();
 
+        code.push(format!(
+            "// fn {name}({}) -> {}",
+            params
+                .iter()
+                .map(|p| format!("{}: {}", p.name, p.type_id))
+                .collect::<Vec<String>>()
+                .join(", "),
+            return_type
+        ));
+
         // Function prologue
         code.push(format!("{}:", name));
         code.push("\tpush bpr".to_string());
@@ -192,7 +209,7 @@ impl CodeGenerator {
 
         // Generate code for function body
         for stmt in body {
-            let stmt_code = self.generate_statement(stmt).unwrap();
+            let stmt_code = self.generate_statement(stmt, &mut code).unwrap();
             code.extend(stmt_code);
         }
 
@@ -211,6 +228,7 @@ impl CodeGenerator {
     fn generate_statement(
         &mut self,
         stmt: &Statement,
+        func_body: &mut Vec<String>,
     ) -> Result<Vec<String>, CompilerError> {
         let mut code = Vec::new();
 
@@ -218,7 +236,8 @@ impl CodeGenerator {
             Statement::Declaration { var, value } => {
                 if let Some(expr) = value {
                     // Evaluate expression
-                    let (result_reg, expr_code) = self.generate_expression(expr, true)?;
+                    let (result_reg, expr_code) =
+                        self.generate_expression(expr, true, func_body)?;
                     code.extend(expr_code);
 
                     // Store result in variable
@@ -233,14 +252,17 @@ impl CodeGenerator {
                 }
             }
 
-            Statement::Break => unimplemented!(),
-            Statement::Continue => unimplemented!(),
+            Statement::Break => unimplemented!("need scope tracking first!"),
+            Statement::Continue => unimplemented!("need scope tracking first!"),
+            Statement::Defer(_func) => unimplemented!("we need scope tracking first!"),
 
             Statement::PtrWrite { ptr, value } => {
-                let (result_reg, expr_code) = self.generate_expression(value, true)?;
+                let (result_reg, expr_code) =
+                    self.generate_expression(value, true, func_body)?;
                 code.extend(expr_code);
 
-                let (ptr_reg, ptr_code) = self.generate_expression(ptr, true)?;
+                let (ptr_reg, ptr_code) =
+                    self.generate_expression(ptr, true, func_body)?;
                 code.extend(ptr_code);
 
                 code.push(format!("\tstw {}, {}", result_reg, ptr_reg));
@@ -251,7 +273,8 @@ impl CodeGenerator {
 
             Statement::Assign { varname, value } => {
                 // Evaluate expression
-                let (result_reg, expr_code) = self.generate_expression(value, true)?;
+                let (result_reg, expr_code) =
+                    self.generate_expression(value, true, func_body)?;
                 code.extend(expr_code);
 
                 // Check if this is a global variable
@@ -270,7 +293,8 @@ impl CodeGenerator {
 
             Statement::Return(expr) => {
                 if let Some(e) = expr {
-                    let (result_reg, expr_code) = self.generate_expression(e, true)?;
+                    let (result_reg, expr_code) =
+                        self.generate_expression(e, true, func_body)?;
                     code.extend(expr_code);
                     code.push(format!("\tstw {}, bpr, 8", result_reg));
                     code.push(format!("\tjmp _ret"));
@@ -284,7 +308,8 @@ impl CodeGenerator {
                 else_stmt,
             } => {
                 // Generate condition
-                let (cond_reg, cond_code) = self.generate_expression(condition, true)?;
+                let (cond_reg, cond_code) =
+                    self.generate_expression(condition, true, func_body)?;
                 code.extend(cond_code);
 
                 // Compare with zero
@@ -302,7 +327,7 @@ impl CodeGenerator {
                 // Then block
                 code.push(format!("{}:", then_label));
                 for s in then_stmt {
-                    code.extend(self.generate_statement(s)?);
+                    code.extend(self.generate_statement(s, func_body)?);
                 }
 
                 if then_stmt.len() == 0 {
@@ -314,7 +339,7 @@ impl CodeGenerator {
                 // Else block
                 code.push(format!("{}:", else_label));
                 for s in else_stmt {
-                    code.extend(self.generate_statement(s)?);
+                    code.extend(self.generate_statement(s, func_body)?);
                 }
 
                 if else_stmt.len() == 0 {
@@ -331,7 +356,8 @@ impl CodeGenerator {
                 code.push(format!("{}:", loop_start));
 
                 // Generate condition
-                let (cond_reg, cond_code) = self.generate_expression(condition, true)?;
+                let (cond_reg, cond_code) =
+                    self.generate_expression(condition, true, func_body)?;
                 code.extend(cond_code);
 
                 code.push(format!("\tcmp {}, zero", cond_reg));
@@ -341,7 +367,7 @@ impl CodeGenerator {
 
                 // Loop body
                 for s in body {
-                    code.extend(self.generate_statement(s)?);
+                    code.extend(self.generate_statement(s, func_body)?);
                 }
 
                 code.push(format!("\tjmp {}", loop_start));
@@ -354,21 +380,22 @@ impl CodeGenerator {
                 code.push(format!("{}:", loop_start));
 
                 for s in body {
-                    code.extend(self.generate_statement(s)?);
+                    code.extend(self.generate_statement(s, func_body)?);
                 }
 
                 code.push(format!("\tjmp {}", loop_start));
             }
 
             Statement::Expression { expr } => {
-                let (result_reg, expr_code) = self.generate_expression(expr, false)?;
+                let (result_reg, expr_code) =
+                    self.generate_expression(expr, false, func_body)?;
                 code.extend(expr_code);
                 self.allocator.free_temp(&result_reg);
             }
 
             Statement::Block(statements) => {
                 for s in statements {
-                    code.extend(self.generate_statement(s)?);
+                    code.extend(self.generate_statement(s, func_body)?);
                 }
             }
         }
@@ -382,14 +409,10 @@ impl CodeGenerator {
         &mut self,
         expr: &Expression,
         use_result: bool,
-    ) -> Result<(String, Vec<String>), CompilerError> {
+        func_body: &mut Vec<String>,
+    ) -> Result<(Register, Vec<String>), CompilerError> {
         let mut code = Vec::new();
 
-        // optimisation to prevent generating dead code!
-        if expr.is_pure() && !use_result {
-            return Ok((String::new(), code));
-        }
-
         match expr {
             Expression::StringLiteral(value) => {
                 let (reg, alloc_code) = self.allocator.alloc_temp()?;
@@ -397,7 +420,7 @@ impl CodeGenerator {
 
                 // write string into memory
                 let uuid = self.get_unique_label();
-                code.push(format!("\tdb str_{uuid}: \"{value}\""));
+                func_body.insert(0, format!("db str_{uuid}: \"{value}\""));
 
                 // Load pointer to string
                 code.push(format!("\tlwi str_{uuid}, {reg}"));
@@ -415,7 +438,7 @@ impl CodeGenerator {
                 Ok((reg, code))
             }
 
-            Expression::Number(value) => {
+            Expression::Number { value, .. } => {
                 let (reg, alloc_code) = self.allocator.alloc_temp()?;
                 code.extend(alloc_code);
 
@@ -446,13 +469,17 @@ impl CodeGenerator {
                 }
             }
 
-            Expression::Binary { op, left, right } => {
+            Expression::Binary {
+                op, left, right, ..
+            } => {
                 // Evaluate left operand
-                let (left_reg, left_code) = self.generate_expression(left, true)?;
+                let (left_reg, left_code) =
+                    self.generate_expression(left, true, func_body)?;
                 code.extend(left_code);
 
                 // Evaluate right operand
-                let (right_reg, right_code) = self.generate_expression(right, true)?;
+                let (right_reg, right_code) =
+                    self.generate_expression(right, true, func_body)?;
                 code.extend(right_code);
 
                 // Allocate result register
@@ -485,50 +512,50 @@ impl CodeGenerator {
                     // Comparison operators - return 1 (true) or 0 (false)
                     BinaryOperator::Eq => {
                         code.push(format!("\tcmp {}, {}", left_reg, right_reg));
-                        code.push(format!("\tlli 0, {}", result_reg));
-                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
-                        code.push(format!("\tjne {}", end_label)); // If not equal, skip setting to 1
                         code.push(format!("\tlli 1, {}", result_reg));
+                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
+                        code.push(format!("\tjeq {}", end_label));
+                        code.push(format!("\tlli 0, {}", result_reg));
                         code.push(format!("{}:", end_label));
                     }
                     BinaryOperator::Ne => {
                         code.push(format!("\tcmp {}, {}", left_reg, right_reg));
-                        code.push(format!("\tlli 0, {}", result_reg));
-                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
-                        code.push(format!("\tjeq {}", end_label)); // If equal, skip setting to 1
                         code.push(format!("\tlli 1, {}", result_reg));
+                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
+                        code.push(format!("\tjne {}", end_label));
+                        code.push(format!("\tlli 0, {}", result_reg));
                         code.push(format!("{}:", end_label));
                     }
                     BinaryOperator::Lt => {
                         code.push(format!("\tcmp {}, {}", left_reg, right_reg));
-                        code.push(format!("\tlli 0, {}", result_reg));
-                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
-                        code.push(format!("\tjge {}", end_label)); // If greater or equal, skip setting to 1
                         code.push(format!("\tlli 1, {}", result_reg));
+                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
+                        code.push(format!("\tjlt {}", end_label));
+                        code.push(format!("\tlli 0, {}", result_reg));
                         code.push(format!("{}:", end_label));
                     }
                     BinaryOperator::Le => {
                         code.push(format!("\tcmp {}, {}", left_reg, right_reg));
-                        code.push(format!("\tlli 0, {}", result_reg));
-                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
-                        code.push(format!("\tjgt {}", end_label)); // If greater than, skip setting to 1
                         code.push(format!("\tlli 1, {}", result_reg));
+                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
+                        code.push(format!("\tjle {}", end_label));
+                        code.push(format!("\tlli 0, {}", result_reg));
                         code.push(format!("{}:", end_label));
                     }
                     BinaryOperator::Gt => {
                         code.push(format!("\tcmp {}, {}", left_reg, right_reg));
-                        code.push(format!("\tlli 0, {}", result_reg));
-                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
-                        code.push(format!("\tjle {}", end_label)); // If less or equal, skip setting to 1
                         code.push(format!("\tlli 1, {}", result_reg));
+                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
+                        code.push(format!("\tjgt {}", end_label));
+                        code.push(format!("\tlli 0, {}", result_reg));
                         code.push(format!("{}:", end_label));
                     }
                     BinaryOperator::Ge => {
                         code.push(format!("\tcmp {}, {}", left_reg, right_reg));
-                        code.push(format!("\tlli 0, {}", result_reg));
-                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
-                        code.push(format!("\tjlt {}", end_label)); // If less than, skip setting to 1
                         code.push(format!("\tlli 1, {}", result_reg));
+                        let end_label = format!("_cmp_end_{}", self.get_unique_label());
+                        code.push(format!("\tjge {}", end_label));
+                        code.push(format!("\tlli 8, {}", result_reg));
                         code.push(format!("{}:", end_label));
                     }
                     _ => unimplemented!(),
@@ -541,11 +568,15 @@ impl CodeGenerator {
                 Ok((result_reg, code))
             }
 
-            Expression::Call { name, args } => {
+            Expression::Call {
+                func: Call { name, args },
+                ..
+            } => {
                 // first evaluate all the args we're going to need
                 let mut arg_regs = Vec::new();
                 for arg in args.iter().rev() {
-                    let (arg_reg, arg_code) = self.generate_expression(arg, true)?;
+                    let (arg_reg, arg_code) =
+                        self.generate_expression(arg, true, func_body)?;
                     code.extend(arg_code);
                     arg_regs.push(arg_reg);
                 }
@@ -561,7 +592,7 @@ impl CodeGenerator {
                 let saved_regs = self.allocator.get_caller_saved_registers();
                 for reg in &saved_regs {
                     // spill variables to stack
-                    code.extend(self.allocator.spill_register(reg).unwrap());
+                    code.extend(self.allocator.free_register(reg).unwrap());
                 }
 
                 // Evaluate and push arguments in reverse order
@@ -587,7 +618,7 @@ impl CodeGenerator {
                     return Err(CompilerError::Undefined(name.clone()));
                 }
 
-                let result_reg: String;
+                let result_reg: Register;
 
                 if use_result {
                     let (temp_result_reg, result_alloc) = self.allocator.alloc_temp()?;
@@ -603,7 +634,7 @@ impl CodeGenerator {
                         }
                     }
                 } else {
-                    result_reg = "zero".to_string();
+                    result_reg = Register::Zero;
 
                     // Clean up arguments
                     if args.len() > 0 {
@@ -626,9 +657,9 @@ impl CodeGenerator {
                 Ok((result_reg, code))
             }
 
-            Expression::Unary { op, operand } => {
+            Expression::Unary { op, operand, .. } => {
                 let (operand_reg, operand_code) =
-                    self.generate_expression(operand, true)?;
+                    self.generate_expression(operand, true, func_body)?;
                 code.extend(operand_code);
 
                 let (result_reg, result_alloc) = self.allocator.alloc_temp()?;
@@ -660,7 +691,7 @@ impl CodeGenerator {
                 Ok((result_reg, code))
             }
 
-            Expression::Empty => Ok(("zero".to_string(), code)),
+            Expression::Empty => Ok((Register::Null, code)),
         }
     }
 
diff --git a/compiler/src/backend/dsa/registers.rs b/compiler/src/backend/dsa/registers.rs
index 00f59e7..3e3453b 100644
--- a/compiler/src/backend/dsa/registers.rs
+++ b/compiler/src/backend/dsa/registers.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::{collections::HashMap, fmt};
 
 use crate::model::CompilerError;
 
@@ -6,78 +6,109 @@ use crate::model::CompilerError;
 /// Manages general-purpose registers (rg0-rgf) and handles stack spilling
 pub struct RegisterAllocator {
     /// Available general-purpose registers
-    available_registers: Vec<String>,
 
     /// Maps variable names to their current location (register or stack offset)
     variable_locations: HashMap<String, Location>,
 
     /// Maps registers to the variables they currently hold
-    register_contents: HashMap<String, String>,
+    register_contents: HashMap<Register, String>,
 
     /// Current stack offset for local variables (relative to bpr)
     /// Starts at -4 (going downward from base pointer)
     stack_offset: i32,
 
     /// Track which registers are currently in use
-    in_use: HashMap<String, bool>,
+    in_use: HashMap<Register, bool>,
 }
 
 #[derive(Debug, Clone)]
-pub enum Location {
-    Register(String),
-    Stack(i32), // offset from bpr
+pub struct Location {
+    register: Option<Register>,
+    stack: Option<i32>,
+}
+
+impl Location {
+    pub fn stack(offset: i32) -> Self {
+        Location {
+            register: None,
+            stack: Some(offset),
+        }
+    }
+
+    pub fn register(register: Register) -> Self {
+        Location {
+            register: Some(register),
+            stack: None,
+        }
+    }
 }
 
 impl RegisterAllocator {
     pub fn new() -> Self {
         // Initialize with available GP registers (rg0-rgf = 16 registers)
-        let registers = vec![
-            "rg0", "rg1", "rg2", "rg3", "rg4", "rg5", "rg6", "rg7", "rg8", "rg9", "rga",
-            "rgb", "rgc", "rgd", "rge", "rgf",
+        let in_use = vec![
+            Register::Rg0,
+            Register::Rg1,
+            Register::Rg2,
+            Register::Rg3,
+            Register::Rg4,
+            Register::Rg5,
+            Register::Rg6,
+            Register::Rg7,
+            Register::Rg8,
+            Register::Rg9,
+            Register::Rga,
+            Register::Rgb,
+            Register::Rgc,
+            Register::Rgd,
+            Register::Rge,
+            Register::Rgf,
         ]
-        .into_iter()
-        .map(String::from)
+        .iter()
+        .map(|&reg| (reg, false))
         .collect();
 
         RegisterAllocator {
-            available_registers: registers,
+            // available_registers: registers,
             variable_locations: HashMap::new(),
             register_contents: HashMap::new(),
             stack_offset: -4, // Start at -4 (first local below saved bpr)
-            in_use: HashMap::new(),
+            in_use,
         }
     }
 
     /// Allocate a temporary register for expression evaluation
     /// Returns the register name and optionally assembly code to save it
-    pub fn alloc_temp(&mut self) -> Result<(String, Vec<String>), CompilerError> {
-        let mut code = Vec::new();
-
+    pub fn alloc_temp(&mut self) -> Result<(Register, Vec<String>), CompilerError> {
         // Try to find an unused register
-        for reg in &self.available_registers {
-            if !self.in_use.get(reg).unwrap_or(&false) {
-                self.in_use.insert(reg.clone(), true);
-                return Ok((reg.clone(), code));
-            }
+
+        println!("finding! {:#?}", self.in_use);
+
+        if let Some(reg) = self.find_free_register() {
+            self.in_use.insert(reg, true);
+            return Ok((reg, Vec::new()));
         }
 
         // All registers in use - need to spill one
         // Choose the first register with a variable we can spill
         // Find a register to spill
-        let reg_to_spill = self
-            .available_registers
-            .iter()
-            .find(|reg| self.register_contents.contains_key(*reg))
-            .cloned();
 
-        if let Some(reg) = reg_to_spill {
-            // Spill this variable to stack
-            let spill_code = self.spill_register(&reg)?;
-            code.extend(spill_code);
+        // let reg_to_spill = self
+        //     .available_registers
+        //     .iter()
+        //     .find(|reg| self.register_contents.contains_key(*reg))
+        //     .cloned();
 
-            self.in_use.insert(reg.clone(), true);
-            return Ok((reg, code));
-        }
+        // if let Some(reg) = reg_to_spill {
+        //     // Spill this variable to stack
+        //     let spill_code = self.spill_register(&reg)?;
+        //     code.extend(spill_code);
+
+        //     self.in_use.insert(reg.clone(), true);
+        //     return Ok((reg, code));
+        // }
+
+        todo!("an efficient stack spilling algorithm. needs scope awareness.");
 
         Err(CompilerError::Generic(
             "All registers are used up yet there are no variables to spill to the stack"
@@ -88,7 +119,7 @@ impl RegisterAllocator {
     /// Free a temporary register after use
     /// NOTE: This will NOT free registers that contain variables!
     /// Variables persist throughout their scope and must not be freed
-    pub fn free_temp(&mut self, reg: &str) {
+    pub fn free_temp(&mut self, reg: &Register) {
         // Check if this register contains a variable
         if self.register_contents.contains_key(reg) {
             // This register holds a variable - don't free it!
@@ -97,7 +128,19 @@ impl RegisterAllocator {
         }
 
         // This is a true temporary - safe to free
-        self.in_use.insert(reg.to_string(), false);
+        self.in_use.insert(*reg, false);
+    }
+
+    pub fn free_var(&mut self, var: &str) {
+        // Check if this variable is in a register
+        if let Some(location) = self.variable_locations.get(var).cloned() {
+            if let Some(reg) = location.register {
+                self.register_contents.remove(&reg);
+                self.in_use.insert(reg, false);
+            }
+
+            self.variable_locations.remove(var);
+        }
     }
 
     /// Allocate a register for a named variable
@@ -105,41 +148,46 @@ impl RegisterAllocator {
     pub fn alloc_var(
         &mut self,
         var_name: &str,
-    ) -> Result<(String, Vec<String>), CompilerError> {
-        if let Some(location) = self.variable_locations.get(var_name).cloned() {
-            match location {
-                Location::Register(reg) => {
-                    return Ok((reg.clone(), Vec::new()));
-                }
-                Location::Stack(offset) => {
-                    // Variable was pushed, need to calculate actual position
-                    let (reg, mut code) = self.alloc_temp()?;
+    ) -> Result<(Register, Vec<String>), CompilerError> {
+        if let Some(mut location) = self.variable_locations.get(var_name).cloned() {
+            // if the var is in a register we can use it already.
+            if let Some(reg) = location.register {
+                return Ok((reg, Vec::new()));
+            }
 
-                    // Load from bpr + offset (offset is negative)
-                    code.push(format!("\tsubi bpr {} {}", -(offset + 4), reg));
-                    code.push(format!(
-                        "\tldw {}, {} // bpr{}: {}",
-                        reg,
-                        reg,
-                        offset - 4,
-                        var_name
-                    ));
+            // if the variable is on the stack only, we need to get it in a register.
+            if let Some(offset) = location.stack {
+                // Variable was pushed, need to calculate actual position and update its
+                // location.
+                let (reg, mut code) = self.alloc_temp()?;
 
-                    // Update location to register
-                    self.variable_locations
-                        .insert(var_name.to_string(), Location::Register(reg.clone()));
-                    self.register_contents
-                        .insert(reg.clone(), var_name.to_string());
+                // acknowledge var is now in a reg as well.
+                location.register = Some(reg);
 
-                    return Ok((reg, code));
-                }
+                // Load from bpr + offset (offset is negative)
+                code.push(format!("\tsubi bpr {} {}", -(offset + 4), reg));
+                code.push(format!(
+                    "\tldw {}, {} // bpr{}: {}",
+                    reg,
+                    reg,
+                    offset - 4,
+                    var_name
+                ));
+
+                // Update location to register
+                self.variable_locations
+                    .insert(var_name.to_string(), location);
+                self.register_contents
+                    .insert(reg.clone(), var_name.to_string());
+
+                return Ok((reg, code));
             }
         }
 
         // Variable doesn't have a location yet, allocate a new register
         let (reg, code) = self.alloc_temp()?;
         self.variable_locations
-            .insert(var_name.to_string(), Location::Register(reg.clone()));
+            .insert(var_name.to_string(), Location::register(reg));
         self.register_contents
             .insert(reg.clone(), var_name.to_string());
 
@@ -156,83 +204,89 @@ impl RegisterAllocator {
     pub fn load_var(
         &mut self,
         var_name: &str,
-    ) -> Result<(String, Vec<String>), CompilerError> {
+    ) -> Result<(Register, Vec<String>), CompilerError> {
         self.alloc_var(var_name)
     }
 
     /// Store a value from a register into a variable
     /// Updates tracking and returns any necessary assembly code
-    pub fn store_var(&mut self, var_name: &str, source_reg: &str) -> Vec<String> {
-        let mut code = Vec::new();
-
+    pub fn store_var(&mut self, var_name: &str, source_reg: &Register) -> Vec<String> {
         // Check if variable already has a location
         if let Some(location) = self.variable_locations.get(var_name) {
-            match location {
-                Location::Register(dest_reg) => {
-                    if dest_reg != source_reg {
-                        code.push(format!(
-                            "\tmov {}, {} // var {}",
-                            source_reg, dest_reg, var_name
-                        ));
-                    }
-                }
-                Location::Stack(offset) => {
-                    code.push(format!(
-                        "\tstw {}, bpr, {} // var {}",
-                        source_reg, offset, var_name
-                    ));
+            // if the variable exists in a register we write to that.
+            if let Some(reg) = location.register {
+                if reg == *source_reg {
+                    return vec![format!(
+                        "\tmov {}, {} // var {}",
+                        source_reg, reg, var_name
+                    )];
                 }
             }
-        } else {
-            // Variable doesn't exist yet, we can just use the same reg.
 
-            // self.variable_locations.insert(
-            //     var_name.to_string(),
-            //     Location::Register(source_reg.to_string()),
-            // );
-            // self.register_contents
-            //     .insert(source_reg.to_string(), var_name.to_string());
-            // self.in_use.insert(source_reg.to_string(), true);
-
-            let source_reg = source_reg.to_string();
-
-            // if we can avoid a move, absolutely do that.
-            if self.available_registers.contains(&source_reg) {
-                self.variable_locations
-                    .insert(var_name.to_string(), Location::Register(source_reg.clone()));
-                self.register_contents
-                    .insert(source_reg.clone(), var_name.to_string());
-                self.in_use.insert(source_reg, true);
-            } else if let Some(free_reg) = self.find_free_register() {
-                code.push(format!("\tmov {}, {}", source_reg, free_reg));
-                self.variable_locations
-                    .insert(var_name.to_string(), Location::Register(free_reg.clone()));
-                self.register_contents
-                    .insert(free_reg.clone(), var_name.to_string());
-                self.in_use.insert(free_reg, true);
-            } else {
-                // No free registers - allocate on stack
-                // code.push(format!("\tstw {}, bpr, {}", source_reg, self.stack_offset));
-                // self.variable_locations
-                //     .insert(var_name.to_string(), Location::Stack(self.stack_offset));
-                // self.stack_offset -= 4; // Move to next stack slot
-                //
-                todo!(
-                    "we should spill other registers and keep this variable on the stack as it's more recent!"
-                );
+            // if the variable exists on the stack but not a register we write here.
+            if let Some(offset) = location.stack {
+                return vec![format!(
+                    "\tstw {}, bpr, {} // var {}",
+                    source_reg, offset, var_name
+                )];
             }
         }
 
-        code
+        // Variable doesn't exist yet, we can just use the same reg.
+        // if we can avoid a move, absolutely do that.
+
+        // if this is true then there's no permanent variable here so it's safe to use.
+        if !self.register_contents.contains_key(source_reg) {
+            self.variable_locations
+                .insert(var_name.to_string(), Location::register(*source_reg));
+            self.register_contents
+                .insert(*source_reg, var_name.to_string());
+            self.in_use.insert(*source_reg, true);
+
+            return Vec::new();
+        }
+
+        // if current register isn't free, (eg is another variable) we assign somewhere
+        // else.
+        if let Some(free_reg) = self.find_free_register() {
+            self.variable_locations
+                .insert(var_name.to_string(), Location::register(free_reg));
+            self.register_contents
+                .insert(free_reg.clone(), var_name.to_string());
+            self.in_use.insert(free_reg, true);
+
+            return vec![format!("\tmov {}, {}", source_reg, free_reg)];
+        }
+
+        // No free registers - allocate on stack
+        // code.push(format!("\tstw {}, bpr, {}", source_reg, self.stack_offset));
+        // self.variable_locations
+        //     .insert(var_name.to_string(), Location::Stack(self.stack_offset));
+        // self.stack_offset -= 4; // Move to next stack slot
+        //
+        todo!("an efficient stack spilling algorithm. needs scope awareness.");
     }
 
-    /// Spill a register to the stack
-    /// Returns assembly code to perform the spill
-    pub fn spill_register(&mut self, reg: &str) -> Result<Vec<String>, CompilerError> {
+    /// spill a register to the stack (WITHOUT FREEING)
+    pub fn spill_register(
+        &mut self,
+        reg: &Register,
+    ) -> Result<Vec<String>, CompilerError> {
         let mut code = Vec::new();
 
-        if let Some(var_name) = self.register_contents.get(reg).cloned() {
-            // PUSH register to stack (spr decrements automatically)
+        // check if the variable is declared.
+        if let Some(var_name) = self.register_contents.get(reg).cloned()
+            && let Some(location) = self.variable_locations.get_mut(&var_name)
+        {
+            // check if var is on the stack
+            if let Some(offset) = location.stack {
+                // ensure stack value is up to date with register value.
+                code.push(format!("\tstw {}, {}", reg, offset));
+                return Ok(code);
+            }
+
+            // if the variable is not on the stack:
+            // push register to stack (spr decrements automatically)
             code.push(format!(
                 "\tpush {} // bpr{}: {}",
                 reg, self.stack_offset, var_name
@@ -240,37 +294,83 @@ impl RegisterAllocator {
 
             // Track that we pushed one word
             self.stack_offset -= 4;
-
             // Update variable location - it's now at current spr
             // Note: We track offset from bpr for consistency
-            self.variable_locations
-                .insert(var_name.clone(), Location::Stack(self.stack_offset));
-
-            // Remove from register tracking
-            self.register_contents.remove(reg);
+            location.stack = Some(self.stack_offset);
+            Ok(code)
+        } else {
+            Err(CompilerError::Generic(format!(
+                "Register {} does not contain a variable to spill!",
+                reg
+            )))
         }
+    }
 
-        Ok(code)
+    /// free a register by spilling it to the stack.
+    /// Returns assembly code to perform the spill
+    pub fn free_register(
+        &mut self,
+        reg: &Register,
+    ) -> Result<Vec<String>, CompilerError> {
+        let mut code = Vec::new();
+
+        // check if the variable is declared.
+        if let Some(var_name) = self.register_contents.get(reg).cloned()
+            && let Some(location) = self.variable_locations.get_mut(&var_name)
+        {
+            // check if var name is on the stack
+            if let Some(offset) = location.stack {
+                // store current register value in stack location
+                code.push(format!("\tstw {}, {}", reg, offset));
+
+                // free the register.
+                location.register = None;
+                self.register_contents.remove(reg);
+                return Ok(code);
+            }
+
+            // if the variable is not on the stack:
+            // push register to stack (spr decrements automatically)
+            code.push(format!(
+                "\tpush {} // bpr{}: {}",
+                reg, self.stack_offset, var_name
+            ));
+
+            // Track that we pushed one word
+            self.stack_offset -= 4;
+            // Update variable location - it's now at current spr
+            // Note: We track offset from bpr for consistency
+            location.stack = Some(self.stack_offset);
+            location.register = None;
+            self.register_contents.remove(reg);
+
+            Ok(code)
+        } else {
+            Err(CompilerError::Generic(format!(
+                "Register {} does not contain a variable to spill!",
+                reg
+            )))
+        }
     }
 
     /// Find a free register (not currently in use)
-    fn find_free_register(&self) -> Option<String> {
-        for reg in &self.available_registers {
-            if !self.in_use.get(reg).unwrap_or(&false) {
-                return Some(reg.clone());
-            }
-        }
-        None
+    fn find_free_register(&self) -> Option<Register> {
+        self.in_use
+            .iter()
+            .filter(|(_, in_use)| !**in_use)
+            .map(|(reg, _)| *reg)
+            .next()
     }
 
     /// Spill all registers to stack (useful before function calls)
     pub fn _spill_all(&mut self) -> Vec<String> {
         let mut code = Vec::new();
 
-        let regs_to_spill: Vec<String> = self.register_contents.keys().cloned().collect();
+        let regs_to_spill: Vec<Register> =
+            self.register_contents.keys().cloned().collect();
 
         for reg in regs_to_spill {
-            if let Ok(spill_code) = self.spill_register(&reg) {
+            if let Ok(spill_code) = self.free_register(&reg) {
                 code.extend(spill_code);
             }
         }
@@ -293,23 +393,43 @@ impl RegisterAllocator {
         self.variable_locations.clear();
         self.register_contents.clear();
         self.stack_offset = -4;
-        self.in_use.clear();
+        self.in_use = vec![
+            Register::Rg0,
+            Register::Rg1,
+            Register::Rg2,
+            Register::Rg3,
+            Register::Rg4,
+            Register::Rg5,
+            Register::Rg6,
+            Register::Rg7,
+            Register::Rg8,
+            Register::Rg9,
+            Register::Rga,
+            Register::Rgb,
+            Register::Rgc,
+            Register::Rgd,
+            Register::Rge,
+            Register::Rgf,
+        ]
+        .iter()
+        .map(|&reg| (reg, false))
+        .collect();
     }
 
     /// Mark a variable as dead (no longer needed)
     /// Frees its register if it's in one
-    pub fn _free_var(&mut self, var_name: &str) {
-        if let Some(Location::Register(reg)) = self.variable_locations.get(var_name) {
-            let reg = reg.clone();
-            self.register_contents.remove(&reg);
-            self.in_use.insert(reg, false);
-        }
-        self.variable_locations.remove(var_name);
-    }
+    // pub fn _free_var(&mut self, var_name: &str) {
+    //     if let Some(Location::Register(reg)) = self.variable_locations.get(var_name) {
+    //         let reg = reg.clone();
+    //         self.register_contents.remove(&reg);
+    //         self.in_use.insert(reg, false);
+    //     }
+    //     self.variable_locations.remove(var_name);
+    // }
 
     /// Get list of registers that contain variables and are in use
     /// These need to be saved before function calls
-    pub fn get_caller_saved_registers(&self) -> Vec<String> {
+    pub fn get_caller_saved_registers(&self) -> Vec<Register> {
         self.register_contents
             .iter()
             .filter(|(reg, _)| *self.in_use.get(*reg).unwrap_or(&false))
@@ -346,3 +466,50 @@ impl RegisterAllocator {
         code
     }
 }
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum Register {
+    Rg0,
+    Rg1,
+    Rg2,
+    Rg3,
+    Rg4,
+    Rg5,
+    Rg6,
+    Rg7,
+    Rg8,
+    Rg9,
+    Rga,
+    Rgb,
+    Rgc,
+    Rgd,
+    Rge,
+    Rgf,
+    Zero,
+    Null,
+}
+
+impl fmt::Display for Register {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Rg0 => write!(f, "rg0"),
+            Self::Rg1 => write!(f, "rg1"),
+            Self::Rg2 => write!(f, "rg2"),
+            Self::Rg3 => write!(f, "rg3"),
+            Self::Rg4 => write!(f, "rg4"),
+            Self::Rg5 => write!(f, "rg5"),
+            Self::Rg6 => write!(f, "rg6"),
+            Self::Rg7 => write!(f, "rg7"),
+            Self::Rg8 => write!(f, "rg8"),
+            Self::Rg9 => write!(f, "rg9"),
+            Self::Rga => write!(f, "rga"),
+            Self::Rgb => write!(f, "rgb"),
+            Self::Rgc => write!(f, "rgc"),
+            Self::Rgd => write!(f, "rgd"),
+            Self::Rge => write!(f, "rge"),
+            Self::Rgf => write!(f, "rgf"),
+            Self::Zero => write!(f, "zero"),
+            Self::Null => write!(f, "null"),
+        }
+    }
+}
diff --git a/compiler/src/frontend/c/parser.rs b/compiler/src/frontend/c/parser.rs
index 9d4c2bf..ec12efb 100644
--- a/compiler/src/frontend/c/parser.rs
+++ b/compiler/src/frontend/c/parser.rs
@@ -351,6 +351,7 @@ impl Parser {
                 op,
                 left: Box::new(expr),
                 right,
+                type_id: None,
             };
         }
 
@@ -371,6 +372,7 @@ impl Parser {
                 op,
                 left: Box::new(expr),
                 right,
+                type_id: None,
             };
         }
 
@@ -391,6 +393,7 @@ impl Parser {
                 op,
                 left: Box::new(expr),
                 right,
+                type_id: None,
             };
         }
 
@@ -407,7 +410,11 @@ impl Parser {
         if let Some(op) = op {
             self.advance();
             let operand = Box::new(self.parse_unary()?);
-            return Ok(Expression::Unary { op, operand });
+            return Ok(Expression::Unary {
+                op,
+                operand,
+                type_id: None,
+            });
         }
 
         self.parse_primary()
@@ -418,7 +425,10 @@ impl Parser {
             TokenType::Number(n) => {
                 let value = *n;
                 self.advance();
-                Ok(Expression::Number(value as isize))
+                Ok(Expression::Number {
+                    value: value as isize,
+                    type_id: None,
+                })
             }
             TokenType::Identifier(name) => {
                 let name = name.clone();
@@ -445,6 +455,7 @@ impl Parser {
                             namespace: None,
                         },
                         args,
+                        type_id: None,
                     })
                 } else {
                     Ok(Expression::Variable {
diff --git a/compiler/src/frontend/dsc/mod.rs b/compiler/src/frontend/dsc/mod.rs
index b4a6666..5718e6f 100644
--- a/compiler/src/frontend/dsc/mod.rs
+++ b/compiler/src/frontend/dsc/mod.rs
@@ -2,11 +2,11 @@ use common::logging::log;
 
 use crate::model::{CompilerError, Program};
 use parser::{ParseResult, Parser};
-use semantic_analyser::Analyser;
+// use semantic_analyser::Analyser;
 
 pub mod lexer;
 pub mod parser;
-pub mod semantic_analyser;
+// pub mod semantic_analyser;
 
 pub fn generate_ast(input: &str) -> Result<Program, CompilerError> {
     log("Tokenising Input...");
@@ -30,8 +30,8 @@ pub fn generate_ast(input: &str) -> Result<Program, CompilerError> {
     log("Analyzing AST...");
     log("Checking Type Information...");
 
-    let analyser = Analyser::new();
-    analyser.analyse(ast.clone()).unwrap();
+    // let mut analyser = Analyser::new();
+    // analyser.analyse(ast.clone()).unwrap();
 
     log("Type Checking Complete...");
     Ok(ast)
diff --git a/compiler/src/frontend/dsc/parser.rs b/compiler/src/frontend/dsc/parser.rs
index 752fbba..2fa533b 100644
--- a/compiler/src/frontend/dsc/parser.rs
+++ b/compiler/src/frontend/dsc/parser.rs
@@ -1,7 +1,7 @@
 use super::lexer::Token;
 use crate::model::{
-    BinaryOperator, Block, CompilerError, ConstExpr, Declaration, Dependency, Expression,
-    Program, Statement, TypeId, UnaryOperator, Variable,
+    BinaryOperator, Block, Call, CompilerError, ConstExpr, Declaration, Dependency,
+    Expression, Program, Statement, TypeId, UnaryOperator, Variable,
 };
 use crate::{expect_tt, expect_value};
 use std::ops::{ControlFlow, FromResidual, Try};
@@ -353,7 +353,7 @@ impl Parser {
         let mut expr = self.parse_additive()?;
 
         while let Some(op) = match self.peek_next()? {
-            Token::EqualEqual => Some(BinaryOperator::Ne),
+            Token::EqualEqual => Some(BinaryOperator::Eq),
             Token::BangEqual => Some(BinaryOperator::Ne),
             Token::Less => Some(BinaryOperator::Lt),
             Token::Greater => Some(BinaryOperator::Gt),
@@ -367,7 +367,8 @@ impl Parser {
                 op,
                 left: Box::new(expr),
                 right,
-            }
+                type_id: Some(TypeId::Bool),
+            };
         }
 
         ParseResult::Accept(expr)
@@ -387,6 +388,7 @@ impl Parser {
             op,
             left: Box::new(left),
             right: Box::new(self.parse_additive()?),
+            type_id: Some(TypeId::U32),
         })
     }
 
@@ -404,6 +406,7 @@ impl Parser {
             op,
             left: Box::new(left),
             right: Box::new(self.parse_multiplicative()?),
+            type_id: None,
         })
     }
 
@@ -418,14 +421,21 @@ impl Parser {
 
         self.next()?;
         let operand = Box::new(self.parse_unary()?);
-        ParseResult::Accept(Expression::Unary { op, operand })
+        ParseResult::Accept(Expression::Unary {
+            op,
+            operand,
+            type_id: None,
+        })
     }
 
     fn parse_primary(&mut self) -> ParseResult<Expression, CompilerError> {
         match self.peek_next()? {
             Token::Integer(value) => {
                 self.next()?;
-                ParseResult::Accept(Expression::Number(value as isize))
+                ParseResult::Accept(Expression::Number {
+                    value: value as isize,
+                    type_id: None,
+                })
             }
             Token::String(value) => {
                 self.next()?;
@@ -450,7 +460,14 @@ impl Parser {
 
                     let _ = expect_tt!(self.next()?, RightParen)?;
 
-                    ParseResult::Accept(Expression::Call { name, args })
+                    ParseResult::Accept(Expression::Call {
+                        func: Call {
+                            name: name.clone(),
+                            args,
+                        },
+
+                        type_id: None,
+                    })
                 } else {
                     ParseResult::Accept(Expression::Variable {
                         name,
diff --git a/compiler/src/frontend/dsc/semantic_analyser.rs b/compiler/src/frontend/dsc/semantic_analyser.rs
index 2b18e2c..9daf780 100644
--- a/compiler/src/frontend/dsc/semantic_analyser.rs
+++ b/compiler/src/frontend/dsc/semantic_analyser.rs
@@ -1,13 +1,226 @@
-use crate::model::{CompilerError, Program};
+use std::collections::HashMap;
 
-pub struct Analyser;
+use crate::model::{
+    BinaryOperator, // You'll need to add this to your imports
+    CompilerError,
+    Declaration,
+    Dependency,
+    Expression,
+    Program,
+    TypeId,
+    UnaryOperator,
+};
+
+pub struct Analyser {
+    symbol_table: HashMap<String, Declaration>,
+}
+
+const NUMERIC_TYPES: &[TypeId] = &[
+    TypeId::U32,
+    TypeId::I32,
+    TypeId::I16,
+    TypeId::U16,
+    TypeId::I8,
+    TypeId::U8,
+];
 
 impl Analyser {
     pub fn new() -> Self {
-        Self
+        Self {
+            symbol_table: HashMap::new(),
+        }
     }
 
-    pub fn analyse(&self, _ast: Program) -> Result<(), CompilerError> {
+    pub fn analyse(&mut self, ast: Program) -> Result<(), CompilerError> {
+        // build table of global symbols.
+        for dec in ast.declarations {
+            let name = match dec.clone() {
+                Declaration::Function { name, .. } => name,
+                Declaration::Variable { var, .. } => var.name,
+                Declaration::Dependency(Dependency { name, .. }) => name,
+            };
+
+            self.symbol_table.insert(name, dec);
+        }
+
         Ok(())
     }
+
+    fn match_type(
+        actual: TypeId,
+        expected: Option<TypeId>,
+    ) -> Result<TypeId, CompilerError> {
+        match expected {
+            Some(id) => {
+                if id != actual {
+                    Err(CompilerError::TypeMismatch(id, actual))
+                } else {
+                    Ok(actual)
+                }
+            }
+            None => Ok(actual),
+        }
+    }
+
+    fn get_type(
+        &mut self, // Changed from &self to &mut self since we modify expr
+        expr: &mut Expression,
+        expected_type: Option<TypeId>,
+    ) -> Result<TypeId, CompilerError> {
+        match expr {
+            // Correct IFF we're expecting a void type
+            Expression::Empty => Self::match_type(TypeId::Void, expected_type),
+
+            // Correct IFF we're expecting a char type
+            Expression::CharLiteral(_) => Self::match_type(TypeId::Char, expected_type),
+
+            // Correct IFF we're expecting a string slice type
+            Expression::StringLiteral(_) => {
+                Self::match_type(TypeId::Ptr(Box::new(TypeId::Char)), expected_type)
+            }
+
+            Expression::Variable { name, expr_type } => {
+                let actual = expr_type.clone().ok_or(CompilerError::UnknownType)?;
+                Self::match_type(actual, expected_type)
+            }
+
+            Expression::Number { value, type_id } => {
+                // If we already know the TypeId
+                if let Some(id) = type_id {
+                    return Self::match_type(id.clone(), expected_type);
+                }
+
+                // If we're expecting a type id, check it's numeric.
+                // TODO: add checks to make sure it's valid for its size eg u8 cant be
+                // more than 255
+                if let Some(expected) = expected_type {
+                    if NUMERIC_TYPES.contains(&expected) {
+                        *type_id = Some(expected.clone());
+                        return Ok(expected);
+                    } else {
+                        return Err(CompilerError::TypeMismatch(expected, TypeId::U32));
+                    }
+                }
+
+                // Default to i32 if no type information is available
+                *type_id = Some(TypeId::I32);
+                Ok(TypeId::I32)
+            }
+
+            Expression::Binary {
+                op,
+                left,
+                right,
+                type_id,
+            } => {
+                // For binary operations, both operands should have compatible types
+                // and the result type depends on the operation
+                let left_type = self.get_type(left, None)?;
+                let right_type = self.get_type(right, Some(left_type.clone()))?;
+
+                // For numeric operations, result has the same type as operands
+                if NUMERIC_TYPES.contains(&left_type)
+                    && NUMERIC_TYPES.contains(&right_type)
+                {
+                    *type_id = Some(left_type);
+                    Self::match_type(left_type, expected_type)
+                } else {
+                    Err(CompilerError::TypeMismatch(left_type, right_type))
+                }
+            }
+
+            Expression::Unary {
+                op,
+                operand,
+                type_id,
+            } => {
+                match op {
+                    UnaryOperator::Plus | UnaryOperator::Minus => {
+                        // Unary +/- require numeric operands
+                        let inner_type = self.get_type(operand, None)?;
+
+                        if NUMERIC_TYPES.contains(&inner_type) {
+                            *type_id = Some(inner_type.clone());
+                            Self::match_type(inner_type, expected_type)
+                        } else {
+                            Err(CompilerError::TypeMismatch(inner_type, TypeId::I32))
+                        }
+                    }
+
+                    UnaryOperator::Dereference => {
+                        // For dereference (*ptr), the operand must be a pointer
+                        // and the result type is what the pointer points to
+                        let inner_type = self.get_type(operand, None)?;
+
+                        match inner_type {
+                            TypeId::Ptr(inner) => {
+                                let deref_type = *inner;
+                                *type_id = Some(deref_type.clone());
+                                Self::match_type(deref_type, expected_type)
+                            }
+                            _ => Err(CompilerError::Generic(format!(
+                                "Cannot dereference non-pointer type: {:?}",
+                                inner_type
+                            ))),
+                        }
+                    }
+
+                    UnaryOperator::Reference => {
+                        // For reference (&var), we need to determine what we're taking
+                        // a reference to, then wrap it in a Ptr
+                        // If expected_type is Ptr(T), then operand should have type T
+                        let expected_inner = match expected_type.clone() {
+                            Some(TypeId::Ptr(inner)) => Some(*inner),
+                            _ => None,
+                        };
+
+                        let inner_type = self.get_type(operand, expected_inner)?;
+                        let ref_type = TypeId::Ptr(Box::new(inner_type));
+                        *type_id = Some(ref_type.clone());
+                        Self::match_type(ref_type, expected_type)
+                    }
+                }
+            }
+
+            Expression::Call {
+                name,
+                args,
+                type_id,
+            } => match self.symbol_table.get(&name.name) {
+                Some(Declaration::Function {
+                    params,
+                    return_type,
+                    ..
+                }) => {
+                    // check that we've given the right number of arguments.
+                    if args.len() != params.len() {
+                        return Err(CompilerError::Generic(format!(
+                            "Function {} expected {} arguments but received {}",
+                            name.name,
+                            params.len(),
+                            args.len()
+                        )));
+                    }
+
+                    for (arg, param) in args.iter_mut().zip(params.iter()) {
+                        // check that the argument type matches the parameter type.
+                        let provided_type = self.get_type(arg, Some(param.type_id))?;
+                        if provided_type != param.type_id {
+                            return Err(CompilerError::TypeMismatch(
+                                param.type_id,
+                                provided_type,
+                            ));
+                        }
+                    }
+
+                    *type_id = Some(return_type.clone());
+                    Self::match_type(return_type.clone(), expected_type)
+                }
+                _ => Err(CompilerError::Generic(format!(
+                    "Function {} not found in symbol table",
+                    name.name
+                ))),
+            },
+        }
+    }
 }
diff --git a/compiler/src/frontend/mod.rs b/compiler/src/frontend/mod.rs
index a17ba62..a9ee921 100644
--- a/compiler/src/frontend/mod.rs
+++ b/compiler/src/frontend/mod.rs
@@ -1,12 +1,12 @@
 use crate::model::{CompilerError, Program};
 
-mod c;
+// mod c;
 mod dsc;
 
 pub fn compiler_frontend(ext: &str, data: &str) -> Result<Program, CompilerError> {
     match ext {
         "dsc" => Ok(dsc::generate_ast(&data)?),
-        "c" => Ok(c::generate_ast(&data)?),
+        // "c" => Ok(c::generate_ast(&data)?),
         _ => Err(CompilerError::Generic(format!(
             "File type {} not supported",
             ext
diff --git a/compiler/src/lib.rs b/compiler/src/lib.rs
index 41fb48b..004cfea 100644
--- a/compiler/src/lib.rs
+++ b/compiler/src/lib.rs
@@ -46,6 +46,8 @@ pub fn compile_file(
         Err(err) => return Err(format!("Compilation failed: {err:?}").into()),
     };
 
+    println!("Parsed AST: {:#?}", ast);
+
     let output_ext = output_path
         .extension()
         .and_then(|s| s.to_str())
diff --git a/compiler/src/model.rs b/compiler/src/model.rs
index 9c7e68e..df1269f 100644
--- a/compiler/src/model.rs
+++ b/compiler/src/model.rs
@@ -9,9 +9,11 @@ pub enum CompilerError {
     Undefined(Name),
     InvalidSyntax(String),
     Generic(String),
+    UnknownType,
+    TypeMismatch(TypeId, TypeId),
 }
 
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Debug, PartialEq, Eq, Clone)]
 pub struct Name {
     pub name: String,
     pub namespace: Option<String>,
@@ -46,7 +48,7 @@ pub struct Dependency {
 }
 
 #[allow(unused)]
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum TypeId {
     U8,
     U16,
@@ -54,18 +56,45 @@ pub enum TypeId {
     I8,
     I16,
     I32,
+    Bool,
     Char,
     Void,
     Ptr(Box<TypeId>),
     Ref(Box<TypeId>),
     Array(Box<TypeId>, usize),
-    Struct { name: Name, fields: Vec<Variable> },
+    Struct { name: Name, fields: Vec<TypeId> },
+}
+
+impl fmt::Display for TypeId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::U8 => write!(f, "u8"),
+            Self::U16 => write!(f, "u16"),
+            Self::U32 => write!(f, "u32"),
+            Self::I8 => write!(f, "i8"),
+            Self::I16 => write!(f, "i16"),
+            Self::I32 => write!(f, "i32"),
+            Self::Bool => write!(f, "bool"),
+            Self::Char => write!(f, "char"),
+            Self::Void => write!(f, "void"),
+            Self::Ptr(t) => write!(f, "*{}", t),
+            Self::Ref(t) => write!(f, "&{}", t),
+            Self::Array(t, len) => write!(f, "[{}; {}]", t, len),
+            Self::Struct { name, fields } => {
+                write!(f, "struct {} {{", name)?;
+                for (i, field) in fields.iter().enumerate() {
+                    write!(f, "{}: {}", i, field)?;
+                }
+                write!(f, "}}")
+            }
+        }
+    }
 }
 
 pub type Block = Vec<Statement>;
 
 #[allow(unused)]
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Variable {
     pub name: String,
     pub type_id: TypeId,
@@ -100,6 +129,7 @@ pub enum Statement {
         body: Vec<Statement>,
     },
     Loop(Block),
+    Defer(Call),
     Break,
     Continue,
     Return(Option<Expression>),
@@ -128,28 +158,47 @@ pub enum Expression {
         op: BinaryOperator,
         left: Box<Expression>,
         right: Box<Expression>,
+
+        // Post-Semantic Analysis
+        type_id: Option<TypeId>,
     },
     Unary {
         op: UnaryOperator,
         operand: Box<Expression>,
+
+        // Post-Semantic Analysis
+        type_id: Option<TypeId>,
     },
     Variable {
         name: Name,
         expr_type: Option<TypeId>,
     },
     Call {
-        name: Name,
-        args: Vec<Expression>,
+        func: Call,
+
+        // Post-Semantic Analysis
+        type_id: Option<TypeId>,
+    },
+    Number {
+        value: isize,
+
+        // Post-Semantic Analysis
+        type_id: Option<TypeId>,
     },
-    Number(isize),
     StringLiteral(String),
     CharLiteral(char),
 }
 
+#[derive(Debug, Clone)]
+pub struct Call {
+    pub name: Name,
+    pub args: Vec<Expression>,
+}
+
 impl Expression {
     pub fn is_pure(&self) -> bool {
         match self {
-            Expression::Number(_) => true,
+            Expression::Number { .. } => true,
             Expression::StringLiteral(_) => true,
             Expression::CharLiteral(_) => true,
             Expression::Call { .. } => false,
@@ -159,6 +208,29 @@ impl Expression {
             Expression::Variable { .. } => true,
         }
     }
+
+    pub fn type_id(&self) -> Result<TypeId, CompilerError> {
+        match self {
+            Expression::Number { type_id, .. } => {
+                type_id.clone().ok_or(CompilerError::UnknownType)
+            }
+            Expression::StringLiteral(_) => Ok(TypeId::Ptr(Box::new(TypeId::Char))),
+            Expression::CharLiteral(_) => Ok(TypeId::Char),
+            Expression::Call { type_id, .. } => {
+                type_id.clone().ok_or(CompilerError::UnknownType)
+            }
+            Expression::Binary { type_id, .. } => {
+                type_id.clone().ok_or(CompilerError::UnknownType)
+            }
+            Expression::Unary { type_id, .. } => {
+                type_id.clone().ok_or(CompilerError::UnknownType)
+            }
+            Expression::Empty => Ok(TypeId::Void),
+            Expression::Variable { expr_type, .. } => {
+                expr_type.clone().ok_or(CompilerError::UnknownType)
+            }
+        }
+    }
 }
 
 #[allow(unused)]