diff --git a/docs/examples/hello_world.srn b/docs/examples/hello_world.srn
index 5a75c30..f3f9083 100644
--- a/docs/examples/hello_world.srn
+++ b/docs/examples/hello_world.srn
@@ -1,3 +1,3 @@
-(def a 4)
+(def a true)
 ;; (defn hello! (name)
 ;;   (println "Hello %s" name))
diff --git a/src/ast.rs b/src/ast.rs
index 10b22cc..b7a35fd 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -58,7 +58,7 @@ impl Expr {
 
 impl Expression for Expr {
     fn eval() {}
-    fn code_gen<'ctx>(&self, compiler: &'ctx Compiler) -> ExprResult<'ctx> {
+    fn code_gen<'ctx, 'val: 'ctx>(&self, compiler: &'ctx mut Compiler<'val>) -> ExprResult<'val> {
         match self {
             Expr::Sym(s) => s.code_gen(compiler),
             Expr::Cons(s) => s.code_gen(compiler),
diff --git a/src/builtins/def.rs b/src/builtins/def.rs
index 0d4e739..f3bcc21 100644
--- a/src/builtins/def.rs
+++ b/src/builtins/def.rs
@@ -14,11 +14,13 @@
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+use crate::ast::Expr;
 use crate::compiler::Compiler;
 use crate::types::collections::core::Seq;
-use crate::types::{ExprResult, List};
+use crate::types::{ExprResult, Expression, List};
+use crate::values::Value;
 
-pub fn def<'a>(compiler: &'a Compiler, args: List) -> ExprResult<'a> {
+pub fn def<'ctx, 'val: 'ctx>(compiler: &'ctx mut Compiler<'val>, args: List) -> ExprResult<'val> {
     // TODO: We need to support docstrings for def
     if args.length() != 2 {
         // TODO: Raise a meaningful error by including the location
@@ -28,12 +30,24 @@ pub fn def<'a>(compiler: &'a Compiler, args: List) -> ExprResult<'a> {
         ));
     }
 
-    //let def_ = &args.first;1
-    let name = args.first();
-    let value = args.rest().first();
+    let sym = match args.first() {
+        Some(e) => match e {
+            Expr::Sym(e) => e,
+            _ => return Err("First argument of 'def' has to be a symbol".to_string()),
+        },
+        _ => return Err("First argument of 'def' has to be a symbol".to_string()),
+    };
 
-    println!("<<<< {:?} \n {:?}", name, value);
-    // TODO: make sure that `def_` is a symbol and its name is "def"
+    let value = match args.rest().first() {
+        Some(e) => {
+            let generated_code = e.code_gen(compiler);
+            Value::new(Some(sym.name.clone()), e, generated_code)
+        }
+        _ => return Err("Missing the second arugment for 'def'.".to_string()),
+    };
 
-    Err("Is not completed".to_string())
+    compiler
+        .current_ns()
+        .unwrap()
+        .define(sym.name.clone(), value, true)
 }
diff --git a/src/compiler.rs b/src/compiler.rs
index 196e69c..62849ec 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -16,7 +16,7 @@
 */
 use inkwell::builder::Builder;
 use inkwell::context::Context;
-use inkwell::passes::PassManager;
+//use inkwell::passes::PassManager;
 use inkwell::values::{AnyValueEnum, BasicValue, FloatValue, FunctionValue, PointerValue};
 
 use crate::namespace::Namespace;
@@ -35,9 +35,9 @@ pub struct Compiler<'ctx> {
     // /// two entries in this hashmap. One would be the ns name itself which
     // /// is `abc.xyz` in this case and the otherone would be
     // /// `/path/to/abc/xyz.srn` file that contains the ns.
-    pub namespaces: HashMap<&'ctx str, Namespace<'ctx>>,
+    pub namespaces: HashMap<String, Namespace<'ctx>>,
     //pub fpm: &'a PassManager<FunctionValue<'ctx>>,
-    current_ns_name: Option<&'ctx str>,
+    current_ns_name: Option<String>,
 }
 
 impl<'ctx> Compiler<'ctx> {
@@ -64,24 +64,28 @@ impl<'ctx> Compiler<'ctx> {
         }
     }
 
-    pub fn create_ns(&mut self, ns_name: &'ctx str) {
-        self.namespaces
-            .insert(ns_name, Namespace::new(&self.context, ns_name));
+    pub fn create_ns(&mut self, ns_name: String, source_file: Option<&'ctx str>) {
+        self.namespaces.insert(
+            ns_name.clone(),
+            Namespace::new(&self.context, ns_name, None),
+        );
     }
 
-    pub fn set_current_ns(&mut self, ns_name: &'ctx str) {
+    pub fn set_current_ns(&mut self, ns_name: String) {
         self.current_ns_name = Some(ns_name);
     }
 
     #[inline]
-    pub fn current_ns(&self) -> Option<&Namespace<'ctx>> {
-        let ns = self.current_ns_name?;
-        self.namespaces.get(ns).map(|x| x)
+    pub fn current_ns(&mut self) -> Option<&mut Namespace<'ctx>> {
+        match &self.current_ns_name {
+            Some(ns) => self.namespaces.get_mut(ns).map(|x| x),
+            _ => None,
+        }
     }
 
     /// Returns the `FunctionValue` representing the function being compiled.
     #[inline]
-    pub fn current_fn(&self) -> FunctionValue<'ctx> {
+    pub fn current_fn(&mut self) -> FunctionValue<'ctx> {
         self.current_ns().unwrap().current_fn()
     }
 
@@ -106,16 +110,16 @@ pub fn create_context() -> Context {
 
 /// Compiles the given `ast` using the given `compiler` into
 /// LLVM IR.
-pub fn compile<'ctx>(
-    compiler: &'ctx Compiler,
+pub fn compile<'ctx, 'val: 'ctx>(
+    compiler: &'ctx mut Compiler<'val>,
     ast: Vec<impl Expression>,
-) -> Vec<Result<AnyValueEnum<'ctx>, String>> {
+) -> Vec<Result<AnyValueEnum<'val>, String>> {
     match compiler.current_ns() {
         Some(ns) => ns,
         None => panic!("Current namespace is not set."),
     };
 
-    let mut generated_code = vec![];
+    let mut generated_code: Vec<Result<AnyValueEnum<'val>, String>> = vec![];
 
     for expr in &ast {
         generated_code.push(expr.code_gen(compiler));
diff --git a/src/main.rs b/src/main.rs
index fd8f107..aa4d4f1 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -39,8 +39,8 @@ fn main() -> io::Result<()> {
     let context = compiler::create_context();
     let mut compiler = compiler::Compiler::new(&context);
 
-    compiler.create_ns("user");
-    compiler.set_current_ns("user");
+    compiler.create_ns("user".to_string(), None);
+    compiler.set_current_ns("user".to_string());
 
     if let Some(input) = args.value_of("INPUT") {
         let mut f = File::open(input)?;
@@ -51,7 +51,7 @@ fn main() -> io::Result<()> {
             Ok(v) => {
                 println!("AST: {:#?}", v);
 
-                let g = compiler::compile(&compiler, v);
+                let g = compiler::compile(&mut compiler, v);
                 println!("GEN: {:?}", g)
             }
             Err(e) => println!(">> error {:?}", e),
diff --git a/src/namespace.rs b/src/namespace.rs
index 6c91118..0c32ff4 100644
--- a/src/namespace.rs
+++ b/src/namespace.rs
@@ -15,9 +15,12 @@
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 use crate::scope::Scope;
+use crate::types::ExprResult;
+use crate::values::Value;
 use inkwell::context::Context;
 use inkwell::module::Module;
-use inkwell::values::FunctionValue;
+use inkwell::types::{AnyTypeEnum, BasicType, FunctionType};
+use inkwell::values::{AnyValueEnum, FunctionValue};
 
 pub struct Namespace<'ctx> {
     /// Each namespace in serene contains it's own LLVM module. You can
@@ -36,9 +39,17 @@ pub struct Namespace<'ctx> {
 }
 
 impl<'ctx> Namespace<'ctx> {
-    pub fn new(context: &'ctx Context, name: &str) -> Namespace<'ctx> {
+    pub fn new(
+        context: &'ctx Context,
+        name: String,
+        source_file: Option<&'ctx str>,
+    ) -> Namespace<'ctx> {
+        let module = context.create_module(&name);
+
+        module.set_source_file_name(source_file.unwrap_or(&name));
+
         Namespace {
-            module: context.create_module(&name),
+            module,
             //scope: Scope::new(None),
             current_fn_opt: None,
             scope: Scope::new(None),
@@ -56,4 +67,58 @@ impl<'ctx> Namespace<'ctx> {
     pub fn current_fn(&self) -> FunctionValue<'ctx> {
         self.current_fn_opt.unwrap()
     }
+
+    fn define_function(
+        &self,
+        name: String,
+        value: Value<'ctx>,
+        public: bool,
+        f: FunctionType<'ctx>,
+    ) -> ExprResult<'ctx> {
+        Err("NotImpelemnted".to_string())
+    }
+
+    fn define_value(
+        &mut self,
+        name: String,
+        value: Value<'ctx>,
+        public: bool,
+        t: impl BasicType<'ctx>,
+    ) -> ExprResult<'ctx> {
+        let c = self.module.add_global(t, None, &name);
+        match value.llvm_value {
+            Ok(v) => {
+                match v {
+                    AnyValueEnum::ArrayValue(a) => c.set_initializer(&a),
+                    AnyValueEnum::IntValue(i) => c.set_initializer(&i),
+                    AnyValueEnum::FloatValue(f) => c.set_initializer(&f),
+                    AnyValueEnum::PointerValue(p) => c.set_initializer(&p),
+                    AnyValueEnum::StructValue(s) => c.set_initializer(&s),
+                    AnyValueEnum::VectorValue(v) => c.set_initializer(&v),
+                    _ => panic!("It shoudn't happen!!!"),
+                };
+
+                self.scope.insert(&name, value, public);
+                Ok(v)
+            }
+
+            Err(e) => Err(e),
+        }
+    }
+
+    pub fn define(&mut self, name: String, value: Value<'ctx>, public: bool) -> ExprResult<'ctx> {
+        match value.llvm_value {
+            Ok(r) => match r.get_type() {
+                AnyTypeEnum::FunctionType(f) => self.define_function(name, value, public, f),
+                AnyTypeEnum::IntType(i) => self.define_value(name, value, public, i),
+                AnyTypeEnum::ArrayType(a) => self.define_value(name, value, public, a),
+                AnyTypeEnum::FloatType(f) => self.define_value(name, value, public, f),
+                AnyTypeEnum::PointerType(p) => self.define_value(name, value, public, p),
+                AnyTypeEnum::StructType(s) => self.define_value(name, value, public, s),
+                AnyTypeEnum::VectorType(v) => self.define_value(name, value, public, v),
+                _ => Err(format!("Data type '{:?}' is not supported", r.get_type())),
+            },
+            Err(e) => Err(e),
+        }
+    }
 }
diff --git a/src/types/collections/list.rs b/src/types/collections/list.rs
index 74138c3..3133bcd 100644
--- a/src/types/collections/list.rs
+++ b/src/types/collections/list.rs
@@ -47,10 +47,11 @@ impl List {
 
 impl Expression for List {
     fn eval() {}
-    fn code_gen<'ctx>(&self, compiler: &'ctx Compiler) -> ExprResult<'ctx> {
+    fn code_gen<'ctx, 'val: 'ctx>(&self, compiler: &'ctx mut Compiler<'val>) -> ExprResult<'val> {
         match self.first() {
             Some(e) => match e {
                 Expr::Sym(s) if s.is_def() => def(compiler, self.rest()),
+
                 _ => Err("Not implemented on list".to_string()),
             },
 
diff --git a/src/types/core.rs b/src/types/core.rs
index a404898..bbf171e 100644
--- a/src/types/core.rs
+++ b/src/types/core.rs
@@ -15,11 +15,13 @@
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 use crate::compiler::Compiler;
-use inkwell::values::AnyValueEnum;
+use inkwell::values::{AnyValue, AnyValueEnum};
 
-pub type ExprResult<'a> = Result<AnyValueEnum<'a>, String>;
+type ExprResultBase<'a, T: AnyValue<'a>> = Result<T, String>;
+
+pub type ExprResult<'a> = ExprResultBase<'a, AnyValueEnum<'a>>;
 
 pub trait Expression {
     fn eval();
-    fn code_gen<'ctx>(&self, compiler: &'ctx Compiler) -> ExprResult<'ctx>;
+    fn code_gen<'ctx, 'val: 'ctx>(&self, compiler: &'ctx mut Compiler<'val>) -> ExprResult<'val>;
 }
diff --git a/src/types/number.rs b/src/types/number.rs
index d4ddb80..95340fd 100644
--- a/src/types/number.rs
+++ b/src/types/number.rs
@@ -46,7 +46,7 @@ impl Eq for Number {}
 
 impl Expression for Number {
     fn eval() {}
-    fn code_gen<'ctx>(&self, compiler: &'ctx Compiler) -> ExprResult<'ctx> {
+    fn code_gen<'ctx, 'val: 'ctx>(&self, compiler: &'ctx mut Compiler<'val>) -> ExprResult<'val> {
         Err("Not implemented on numbers".to_string())
     }
 }
diff --git a/src/types/symbol.rs b/src/types/symbol.rs
index b8e9557..4613af4 100644
--- a/src/types/symbol.rs
+++ b/src/types/symbol.rs
@@ -16,6 +16,7 @@
 */
 use crate::compiler::Compiler;
 use crate::types::core::{ExprResult, Expression};
+use inkwell::types::IntType;
 use inkwell::values::AnyValueEnum;
 
 #[derive(Debug, Clone)]
@@ -33,8 +34,8 @@ impl Eq for Symbol {}
 
 impl Expression for Symbol {
     fn eval() {}
-    fn code_gen<'ctx>(&self, compiler: &'ctx Compiler) -> ExprResult<'ctx> {
-        let bool_t = compiler.context.bool_type();
+    fn code_gen<'ctx, 'val: 'ctx>(&self, compiler: &'ctx mut Compiler<'val>) -> ExprResult<'val> {
+        let bool_t: IntType<'val> = compiler.context.bool_type();
         if self.name == "true" {
             Ok(AnyValueEnum::IntValue(bool_t.const_int(1, false)))
         } else if self.name == "false" {
diff --git a/src/values.rs b/src/values.rs
index 4b5c32e..8b0fdb8 100644
--- a/src/values.rs
+++ b/src/values.rs
@@ -15,10 +15,21 @@
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 use crate::ast::Expr;
-use inkwell::values::AnyValueEnum;
+use crate::types::ExprResult;
 
+#[derive(Debug, Eq, PartialEq, Clone)]
 pub struct Value<'a> {
-    llvm_id: Option<&'a str>,
-    lllvm_value: AnyValueEnum<'a>,
-    expr: &'a Expr,
+    pub llvm_id: Option<String>,
+    pub llvm_value: ExprResult<'a>,
+    pub expr: Expr,
+}
+
+impl<'a> Value<'a> {
+    pub fn new(name: Option<String>, expr: Expr, value: ExprResult<'a>) -> Value {
+        Value {
+            llvm_id: name,
+            llvm_value: value,
+            expr: expr,
+        }
+    }
 }