diff --git a/bin/serene.cpp b/bin/serene.cpp
index 78f3275..f4ff2c5 100644
--- a/bin/serene.cpp
+++ b/bin/serene.cpp
@@ -60,7 +60,13 @@ int main(int argc, char *argv[]) {
   case Action::DumpIR: {
     reader::FileReader *r = new reader::FileReader(inputFile);
 
-    serene::sir::dumpSIR(*r->read());
+    auto ast = r->read();
+
+    if (!ast) {
+      throw ast.takeError();
+    }
+
+    serene::sir::dumpSIR(*ast);
     delete r;
     return 0;
   }
diff --git a/include/serene/errors.h b/include/serene/errors.h
new file mode 100644
index 0000000..0188302
--- /dev/null
+++ b/include/serene/errors.h
@@ -0,0 +1,31 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef SERENE_ERRORS_H
+#define SERENE_ERRORS_H
+
+#include "serene/errors/errc.h"
+#include "serene/errors/error.h"
+
+#endif
diff --git a/include/serene/errors/errc.h b/include/serene/errors/errc.h
new file mode 100644
index 0000000..0238cdf
--- /dev/null
+++ b/include/serene/errors/errc.h
@@ -0,0 +1,83 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef SERENE_ERRORS_ERRC_H
+#define SERENE_ERRORS_ERRC_H
+
+#include "llvm/Support/Errc.h"
+
+namespace serene {
+
+/// A collection of common error codes in Serene
+enum class errc {
+  argument_list_too_long = int(std::errc::argument_list_too_long),
+  argument_out_of_domain = int(std::errc::argument_out_of_domain),
+  bad_address = int(std::errc::bad_address),
+  bad_file_descriptor = int(std::errc::bad_file_descriptor),
+  broken_pipe = int(std::errc::broken_pipe),
+  device_or_resource_busy = int(std::errc::device_or_resource_busy),
+  directory_not_empty = int(std::errc::directory_not_empty),
+  executable_format_error = int(std::errc::executable_format_error),
+  file_exists = int(std::errc::file_exists),
+  file_too_large = int(std::errc::file_too_large),
+  filename_too_long = int(std::errc::filename_too_long),
+  function_not_supported = int(std::errc::function_not_supported),
+  illegal_byte_sequence = int(std::errc::illegal_byte_sequence),
+  inappropriate_io_control_operation =
+      int(std::errc::inappropriate_io_control_operation),
+  interrupted = int(std::errc::interrupted),
+  invalid_argument = int(std::errc::invalid_argument),
+  invalid_seek = int(std::errc::invalid_seek),
+  io_error = int(std::errc::io_error),
+  is_a_directory = int(std::errc::is_a_directory),
+  no_child_process = int(std::errc::no_child_process),
+  no_lock_available = int(std::errc::no_lock_available),
+  no_space_on_device = int(std::errc::no_space_on_device),
+  no_such_device_or_address = int(std::errc::no_such_device_or_address),
+  no_such_device = int(std::errc::no_such_device),
+  no_such_file_or_directory = int(std::errc::no_such_file_or_directory),
+  no_such_process = int(std::errc::no_such_process),
+  not_a_directory = int(std::errc::not_a_directory),
+  not_enough_memory = int(std::errc::not_enough_memory),
+  not_supported = int(std::errc::not_supported),
+  operation_not_permitted = int(std::errc::operation_not_permitted),
+  permission_denied = int(std::errc::permission_denied),
+  read_only_file_system = int(std::errc::read_only_file_system),
+  resource_deadlock_would_occur = int(std::errc::resource_deadlock_would_occur),
+  resource_unavailable_try_again =
+      int(std::errc::resource_unavailable_try_again),
+  result_out_of_range = int(std::errc::result_out_of_range),
+  too_many_files_open_in_system = int(std::errc::too_many_files_open_in_system),
+  too_many_files_open = int(std::errc::too_many_files_open),
+  too_many_links = int(std::errc::too_many_links)
+};
+
+/// The **official way** to create `std::error_code` in context of Serene.
+inline std::error_code make_error_code(errc E) {
+  return std::error_code(static_cast<int>(E), std::generic_category());
+};
+
+}; // namespace serene
+
+#endif
diff --git a/include/serene/errors/error.h b/include/serene/errors/error.h
new file mode 100644
index 0000000..26c6d9f
--- /dev/null
+++ b/include/serene/errors/error.h
@@ -0,0 +1,30 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef SERENE_ERRORS_ERROR_H
+#define SERENE_ERRORS_ERROR_H
+
+#include "llvm/Support/Error.h"
+
+#endif
diff --git a/include/serene/exprs/expression.h b/include/serene/exprs/expression.h
index 1ef6ea1..dd23194 100644
--- a/include/serene/exprs/expression.h
+++ b/include/serene/exprs/expression.h
@@ -30,136 +30,67 @@
 
 namespace serene {
 
-/// Contains all the builtin expressions including those which do not appear in
-/// the syntax directly. Like function definitions.
+/// Contains all the builtin AST expressions including those which do not appear
+/// in the syntax directly. Like function definitions.
 namespace exprs {
 
 /// This enum represent the expression type and **not** the value type.
 enum class ExprType {
   Symbol,
   List,
+  Number,
 };
 
-/// The polymorphic type that works as the entry point to the exprs system.
-/// Each expression has to define the interface of the `ExpressionConcept`
-/// class as generic functions. **REMEMBER TO NOT INHERIT FROM THESE CLASSES**
+/// The base class of the expressions which provides the common interface for
+/// the expressions to implement.
 class Expression {
 public:
+  /// The location range provide information regarding to where in the input
+  /// string the current expression is used.
   reader::LocationRange location;
 
   Expression(const reader::LocationRange &loc) : location(loc){};
   virtual ~Expression() = default;
 
+  /// Returns the type of the expression. We need this funciton to perform
+  /// dynamic casting of expression object to implementations such as lisp or
+  /// symbol.
   virtual ExprType getType() const = 0;
+
+  /// The AST representation of an expression
   virtual std::string toString() const = 0;
 };
+using node = std::shared_ptr<Expression>;
+using ast = llvm::SmallVector<node, 0>;
 
-/// Create a new Expression of type `T` and forwards any given parameter
+/// Create a new `node` of type `T` and forwards any given parameter
 /// to the constructor of type `T`. This is the **official way** to create
 /// a new `Expression`. Here is an example:
 /// \code
-/// auto list = Expression::make<List>();
+/// auto list = make<List>();
 /// \endcode
 ///
-/// \param loc A `serene::reader::LocationRange` instance to point to exact
-/// location of the expression in the input string.
 /// \param[args] Any argument with any type passed to this function will be
 ///              passed to the constructor of type T.
-/// \return A new expression containing a value of type T and act as tyep T.
-// template <typename T, typename... Args> std::shared_ptr<T> make(Args
-// &&...args);
-template <typename T, typename... Args>
-std::shared_ptr<T> make(Args &&...args) {
+/// \return A shared pointer to an Expression
+template <typename T, typename... Args> node make(Args &&...args) {
   return std::shared_ptr<T>(new T(std::forward<Args>(args)...));
 };
 
-using node = std::shared_ptr<Expression>;
-using ast = llvm::SmallVector<node, 0>;
-// /// Creates a new expression by moving the given object of the type T into
-// /// a new internal container.
-// ///
-// /// \param e and expression of type T
-// template <typename T> Expression(T e) : self(new Impl<T>(std::move(e))){};
-
-// /// The copy constructor which actually just move the other expression into
-// /// a new implementation container.
-// ///
-// /// \param e is the other expression to copy from
-// Expression(const Expression &e) : self(e.self->copy_()){}; // Copy ctor
-// Expression(Expression &&e) noexcept = default;             // Move ctor
-
-// Expression &operator=(const Expression &e);
-// Expression &operator=(Expression &&e) noexcept = default;
-
-// /// Returns the type of the expression. More precisely, It returns the type
-// /// of the expression that it contains.
-// ///
-// /// \return The type of expression.
-// ExprType getType();
-
-// /// Return the string representation of the expression in the context
-// /// of the AST. Think of it as dump of the AST for each expression.
-// ///
-// /// \return the exoression in string format.
-// std::string toString();
-
-// /// Create a new Expression of type `T` and forwards any given parameter
-// /// to the constructor of type `T`. This is the **official way** to create
-// /// a new `Expression`. Here is an example:
-// /// \code
-// /// auto list = Expression::make<List>();
-// /// \endcode
-// ///
-// /// \param loc A `serene::reader::LocationRange` instance to point to exact
-// /// location of the expression in the input string.
-// /// \param[args] Any argument with any type passed to this function will be
-// ///              passed to the constructor of type T.
-// /// \return A new expression containing a value of type T and act as tyep T.
-// template <typename T, typename... Args>
-// static Expression make(Args &&...args) {
-//   return Expression(T(std::forward<Args>(args)...));
-// };
-
-// template <typename T> std::unique_ptr<T> *to();
-// // template <typename T> static Expression make(reader::LocationRange &&loc)
-// {
-// //   Expression e(T(std::forward<reader::LocationRange>(loc)));
-// //   return e;
-// // };
-
-// /// The generic interface which each type of expression has to implement
-// /// in order to act like an `Expression`
-// class ExpressionConcept {
-// public:
-//   virtual ~ExpressionConcept() = default;
-//   virtual ExpressionConcept *copy_() const = 0;
-
-//   /// Return the type of the expression
-//   virtual ExprType getType() = 0;
-
-//   /// Return the string representation of the expression in the context
-//   /// of the AST. Think of it as dump of the AST for each expression
-//   virtual std::string toString() = 0;
-// };
-
-// /// The generic implementation of `ExpressionConcept` which acts as the
-// /// dispatcher on type.
-// template <typename T> struct Impl : ExpressionConcept {
-//   Impl(T e) : expr(std::move(e)){};
-
-//   ExpressionConcept *copy_() const { return new Impl(*this); }
-
-//   /// In order to make llvm's RTTI to work we need this method.
-//   ExprType getType() const { return expr.getType(); }
-
-//   std::string toString() { return expr.toString(); }
-
-//   T expr;
-// };
-
-// /// The internal container to keep the object implementing the
-// /// `ExpressionConcept`. This might be a `List` for example or a `Symbol`.
-// std::unique_ptr<ExpressionConcept> self;
+/// Create a new `node` of type `T` and forwards any given parameter
+/// to the constructor of type `T`. This is the **official way** to create
+/// a new `Expression`. Here is an example:
+/// \code
+/// auto list = make<List>();
+/// \endcode
+///
+/// \param[args] Any argument with any type passed to this function will be
+///              passed to the constructor of type T.
+/// \return A shared pointer to a value of type T.
+template <typename T, typename... Args>
+std::shared_ptr<T> makeAndCast(Args &&...args) {
+  return std::shared_ptr<T>(new T(std::forward<Args>(args)...));
+};
 
 } // namespace exprs
 } // namespace serene
diff --git a/include/serene/exprs/list.h b/include/serene/exprs/list.h
index 8bef7e5..95b6c0a 100644
--- a/include/serene/exprs/list.h
+++ b/include/serene/exprs/list.h
@@ -33,8 +33,12 @@ namespace serene {
 
 namespace exprs {
 
+/// This class represents a List in the AST level and not the List as the data
+/// type.
 class List : public Expression {
 public:
+  // Internal elements of the lest (small vector of shared pointers to
+  // expressions)
   ast elements;
 
   List(const List &l);               // Copy ctor
@@ -47,6 +51,8 @@ public:
   ExprType getType() const;
   std::string toString() const;
 
+  void append(node);
+
   static bool classof(const Expression *e);
 
   ~List() = default;
diff --git a/include/serene/exprs/number.h b/include/serene/exprs/number.h
new file mode 100644
index 0000000..ebed3e7
--- /dev/null
+++ b/include/serene/exprs/number.h
@@ -0,0 +1,59 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef EXPRS_NUMBER_H
+#define EXPRS_NUMBER_H
+
+#include "serene/exprs/expression.h"
+
+namespace serene {
+
+namespace exprs {
+
+/// This data structure represent the Lisp symbol. Just a symbol
+/// in the context of the AST and nothing else.
+struct Number : public Expression {
+  std::string value;
+
+  bool isNeg;
+  bool isFloat;
+
+  Number(reader::LocationRange &loc, const std::string &num, bool isNeg,
+         bool isFloat)
+      : Expression(loc), value(num), isNeg(isNeg), isFloat(isFloat){};
+
+  ExprType getType() const;
+  std::string toString() const;
+
+  int64_t toI64();
+
+  static bool classof(const Expression *e);
+
+  ~Number() = default;
+};
+
+} // namespace exprs
+} // namespace serene
+
+#endif
diff --git a/include/serene/exprs/symbol.h b/include/serene/exprs/symbol.h
index 68b2078..91fc3d6 100644
--- a/include/serene/exprs/symbol.h
+++ b/include/serene/exprs/symbol.h
@@ -33,6 +33,8 @@ namespace serene {
 
 namespace exprs {
 
+/// This data structure represent the Lisp symbol. Just a symbol
+/// in the context of the AST and nothing else.
 struct Symbol : public Expression {
   std::string name;
 
diff --git a/include/serene/namespace.hpp b/include/serene/namespace.h
similarity index 88%
rename from include/serene/namespace.hpp
rename to include/serene/namespace.h
index 7b20670..d1cd9eb 100644
--- a/include/serene/namespace.hpp
+++ b/include/serene/namespace.h
@@ -27,18 +27,15 @@
 
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/Value.h"
-#include "serene/expr.hpp"
+#include "serene/exprs/expression.h"
 #include "serene/llvm/IR/Value.h"
 #include "serene/logger.hpp"
 #include "llvm/ADT/DenseMap.h"
 #include <llvm/IR/Module.h>
 #include <string>
 
-#if defined(ENABLE_LOG) || defined(ENABLE_NAMESPACE_LOG)
-#define NAMESPACE_LOG(...) __LOG("NAMESPACE", __VA_ARGS__);
-#else
-#define NAMESPACE_LOG(...) ;
-#endif
+#define NAMESPACE_LOG(...)                                                     \
+  DEBUG_WITH_TYPE("NAMESPACE", llvm::dbgs() << __VA_ARGS__ << "\n");
 
 using ScopeMap = llvm::DenseMap<llvm::StringRef, mlir::Value>;
 using PairT = std::pair<llvm::StringRef, mlir::Value>;
@@ -48,7 +45,7 @@ class AExpr;
 
 class Namespace {
 private:
-  ast_tree tree{};
+  exprs::ast tree{};
   bool initialized = false;
 
   ScopeMap rootScope;
@@ -59,8 +56,8 @@ public:
 
   Namespace(llvm::StringRef ns_name, llvm::Optional<llvm::StringRef> filename);
 
-  ast_tree &Tree();
-  mlir::LogicalResult setTree(ast_tree);
+  exprs::ast &Tree();
+  mlir::LogicalResult setTree(exprs::ast &);
   // TODO: Fix it to return llvm::Optional<mlir::Value> instead
   llvm::Optional<mlir::Value> lookup(llvm::StringRef name);
   mlir::LogicalResult insert_symbol(llvm::StringRef name, mlir::Value v);
diff --git a/include/serene/reader/errors.h b/include/serene/reader/errors.h
new file mode 100644
index 0000000..01288fe
--- /dev/null
+++ b/include/serene/reader/errors.h
@@ -0,0 +1,64 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef SERENE_READER_ERRORS_H
+#define SERENE_READER_ERRORS_H
+#include "serene/errors.h"
+
+namespace serene {
+namespace reader {
+
+class ReadError : public std::exception {
+private:
+  char *message;
+
+public:
+  ReadError(char *msg) : message(msg){};
+  const char *what() const throw() { return message; }
+};
+
+class MissingFileError : public llvm::ErrorInfo<MissingFileError> {
+
+  using llvm::ErrorInfo<MissingFileError>::log;
+  using llvm::ErrorInfo<MissingFileError>::convertToErrorCode;
+
+public:
+  static char ID;
+  std::string path;
+
+  // TODO: Move this to an error namespace somewhere.
+  int file_is_missing = int();
+
+  void log(llvm::raw_ostream &os) const {
+    os << "File does not exist: " << path << "\n";
+  }
+
+  MissingFileError(llvm::StringRef path) : path(path.str()){};
+  std::error_code convertToErrorCode() const {
+    return make_error_code(errc::no_such_file_or_directory);
+  }
+};
+} // namespace reader
+} // namespace serene
+#endif
diff --git a/include/serene/reader/reader.h b/include/serene/reader/reader.h
index e23d9f0..8640e78 100644
--- a/include/serene/reader/reader.h
+++ b/include/serene/reader/reader.h
@@ -29,15 +29,19 @@
 #include <sstream>
 #include <stdexcept>
 #include <string>
+#include <system_error>
 #include <vector>
 
-#include "serene/expr.hpp"
-#include "serene/list.hpp"
+#include "serene/errors.h"
+#include "serene/exprs/expression.h"
+#include "serene/exprs/list.h"
+#include "serene/exprs/symbol.h"
 #include "serene/logger.hpp"
+#include "serene/reader/errors.h"
 #include "serene/reader/location.h"
 #include "serene/serene.h"
-#include "serene/symbol.hpp"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
 
 #define READER_LOG(...)                                                        \
   DEBUG_WITH_TYPE("READER", llvm::dbgs() << __VA_ARGS__ << "\n");
@@ -45,15 +49,6 @@
 namespace serene {
 namespace reader {
 
-class ReadError : public std::exception {
-private:
-  char *message;
-
-public:
-  ReadError(char *msg) : message(msg){};
-  const char *what() const throw() { return message; }
-};
-
 class Reader {
 private:
   char current_char = ';'; // Some arbitary char to begin with
@@ -65,19 +60,19 @@ private:
   bool isValidForIdentifier(char c);
 
   // The property to store the ast tree
-  ast_tree ast;
-  ast_node readSymbol();
-  ast_node readNumber(bool);
-  ast_list_node readList();
-  ast_node readExpr();
+  exprs::ast ast;
+  exprs::node readSymbol();
+  exprs::node readNumber(bool);
+  exprs::node readList();
+  exprs::node readExpr();
 
 public:
   Reader() : input_stream(""){};
-  Reader(const std::string);
+  Reader(const llvm::StringRef string);
 
-  void setInput(const std::string);
+  void setInput(const llvm::StringRef string);
 
-  std::unique_ptr<ast_tree> read();
+  llvm::Expected<exprs::ast> read();
 
   // Dumps the AST data to stdout
   void dumpAST();
@@ -95,7 +90,7 @@ public:
   // Dumps the AST data to stdout
   void dumpAST();
 
-  std::unique_ptr<ast_tree> read();
+  llvm::Expected<exprs::ast> read();
 
   ~FileReader();
 };
diff --git a/include/serene/sir/generator.hpp b/include/serene/sir/generator.hpp
index fe913f4..be8ad7c 100644
--- a/include/serene/sir/generator.hpp
+++ b/include/serene/sir/generator.hpp
@@ -30,7 +30,7 @@
 #include "mlir/IR/MLIRContext.h"
 #include "serene/expr.hpp"
 #include "serene/list.hpp"
-#include "serene/namespace.hpp"
+#include "serene/namespace.h"
 #include "serene/number.hpp"
 #include "serene/symbol.hpp"
 #include "llvm/ADT/ScopedHashTable.h"
diff --git a/include/serene/sir/sir.hpp b/include/serene/sir/sir.hpp
index 1dcd797..a2ed24a 100644
--- a/include/serene/sir/sir.hpp
+++ b/include/serene/sir/sir.hpp
@@ -26,7 +26,7 @@
 
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/MLIRContext.h"
-#include "serene/expr.hpp"
+#include "serene/exprs/expression.h"
 #include "serene/sir/generator.hpp"
 #include <memory>
 
@@ -41,12 +41,12 @@ private:
 public:
   SIR();
 
-  mlir::OwningModuleRef generate(::serene::Namespace *ns);
+  mlir::OwningModuleRef generate(serene::Namespace *ns);
 
   ~SIR();
 };
 
-void dumpSIR(ast_tree &t);
+void dumpSIR(exprs::ast &t);
 } // namespace sir
 
 } // namespace serene
diff --git a/include/serene/state.hpp b/include/serene/state.hpp
index 979edae..5d4e0b5 100644
--- a/include/serene/state.hpp
+++ b/include/serene/state.hpp
@@ -27,7 +27,7 @@
 
 #include "serene/llvm/IR/Value.h"
 #include "serene/logger.hpp"
-//#include "serene/namespace.hpp"
+//#include "serene/namespace.h"
 #include <llvm/IR/Module.h>
 #include <string>
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0368fda..c8e916e 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -4,10 +4,16 @@ set(HEADER_LIST
   "${INCLUDE_DIR}/serene/exprs/expression.h"
   "${INCLUDE_DIR}/serene/exprs/symbol.h"
   "${INCLUDE_DIR}/serene/exprs/list.h"
+  "${INCLUDE_DIR}/serene/exprs/number.h"
 
   # Reader
   "${INCLUDE_DIR}/serene/reader/reader.h"
   "${INCLUDE_DIR}/serene/reader/location.h"
+  "${INCLUDE_DIR}/serene/reader/errors.h"
+
+  "${INCLUDE_DIR}/serene/errors.h"
+  "${INCLUDE_DIR}/serene/errors/error.h"
+  "${INCLUDE_DIR}/serene/errors/errc.h"
 
 
   "${INCLUDE_DIR}/serene/expr.hpp"
@@ -23,13 +29,15 @@ set(HEADER_LIST
   "${INCLUDE_DIR}/serene/sir/sir.hpp"
   "${INCLUDE_DIR}/serene/sir/dialect.hpp"
   "${INCLUDE_DIR}/serene/sir/generator.hpp"
-  "${INCLUDE_DIR}/serene/namespace.hpp")
+  "${INCLUDE_DIR}/serene/namespace.h")
 
 # Make an automatic library - will be static or dynamic based on user setting
 add_library(serene
   exprs/expression.cpp
   exprs/symbol.cpp
   exprs/list.cpp
+  exprs/number.cpp
+
 
   serene.cpp
   symbol.cpp
@@ -42,6 +50,7 @@ add_library(serene
   # Reader
   reader/reader.cpp
   reader/location.cpp
+  reader/errors.cpp
 
   # IR
   sir/sir.cpp
diff --git a/src/error.cpp b/src/error.cpp
index 56631e6..708ac9b 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -25,7 +25,7 @@
 #include "serene/error.hpp"
 #include "serene/expr.hpp"
 #include "serene/llvm/IR/Value.h"
-#include "serene/namespace.hpp"
+#include "serene/namespace.h"
 #include "serene/state.hpp"
 #include <assert.h>
 #include <fmt/core.h>
diff --git a/src/exprs/list.cpp b/src/exprs/list.cpp
index 58027f9..47eb092 100644
--- a/src/exprs/list.cpp
+++ b/src/exprs/list.cpp
@@ -53,5 +53,6 @@ bool List::classof(const Expression *e) {
   return e->getType() == ExprType::List;
 };
 
+void List::append(node n) { elements.push_back(n); }
 } // namespace exprs
 } // namespace serene
diff --git a/src/exprs/number.cpp b/src/exprs/number.cpp
new file mode 100644
index 0000000..004b11e
--- /dev/null
+++ b/src/exprs/number.cpp
@@ -0,0 +1,50 @@
+/*
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "serene/exprs/number.h"
+#include "llvm/Support/FormatVariadic.h"
+
+namespace serene {
+namespace exprs {
+
+int64_t Number::toI64() {
+  // TODO: Handle float case as well
+  // TODO: Cache the value
+  return std::stoi(value);
+};
+
+ExprType Number::getType() const { return ExprType::Number; };
+
+std::string Number::toString() const {
+  return llvm::formatv("<Symbol [loc: {0} | {1}]: {2}>",
+                       this->location.start.toString(),
+                       this->location.end.toString(), this->value);
+}
+
+bool Number::classof(const Expression *e) {
+  return e->getType() == ExprType::Number;
+};
+
+} // namespace exprs
+} // namespace serene
diff --git a/src/exprs/symbol.cpp b/src/exprs/symbol.cpp
index 5c036cf..85d021c 100644
--- a/src/exprs/symbol.cpp
+++ b/src/exprs/symbol.cpp
@@ -28,7 +28,6 @@
 namespace serene {
 namespace exprs {
 
-
 ExprType Symbol::getType() const { return ExprType::Symbol; };
 
 std::string Symbol::toString() const {
@@ -37,7 +36,7 @@ std::string Symbol::toString() const {
                        this->location.end.toString(), this->name);
 }
 
-  bool Symbol::classof(const Expression *e) {
+bool Symbol::classof(const Expression *e) {
   return e->getType() == ExprType::List;
 };
 
diff --git a/src/namespace.cpp b/src/namespace.cpp
index 085cc77..1a93dde 100644
--- a/src/namespace.cpp
+++ b/src/namespace.cpp
@@ -22,8 +22,8 @@
  * SOFTWARE.
  */
 
-#include "serene/namespace.hpp"
-#include "serene/expr.hpp"
+#include "serene/namespace.h"
+#include "serene/exprs/expression.h"
 #include "serene/llvm/IR/Value.h"
 #include "llvm/ADT/StringRef.h"
 #include <fmt/core.h>
@@ -41,7 +41,7 @@ Namespace::Namespace(llvm::StringRef ns_name,
   this->name = ns_name;
 };
 
-ast_tree &Namespace::Tree() { return this->tree; }
+exprs::ast &Namespace::Tree() { return this->tree; }
 
 llvm::Optional<mlir::Value> Namespace::lookup(llvm::StringRef name) {
   if (auto value = rootScope.lookup(name)) {
@@ -51,7 +51,7 @@ llvm::Optional<mlir::Value> Namespace::lookup(llvm::StringRef name) {
   return llvm::None;
 };
 
-mlir::LogicalResult Namespace::setTree(ast_tree t) {
+mlir::LogicalResult Namespace::setTree(exprs::ast &t) {
   if (initialized) {
     return mlir::failure();
   }
diff --git a/src/number.cpp b/src/number.cpp
index 39da1fc..4977d92 100644
--- a/src/number.cpp
+++ b/src/number.cpp
@@ -25,7 +25,7 @@
 #include "serene/number.hpp"
 #include "serene/expr.hpp"
 #include "serene/llvm/IR/Value.h"
-#include "serene/namespace.hpp"
+#include "serene/namespace.h"
 #include "serene/state.hpp"
 #include <assert.h>
 #include <fmt/core.h>
diff --git a/src/reader/errors.cpp b/src/reader/errors.cpp
new file mode 100644
index 0000000..965e828
--- /dev/null
+++ b/src/reader/errors.cpp
@@ -0,0 +1,32 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "serene/reader/errors.h"
+
+namespace serene {
+namespace reader {
+/// This one should be here, llvm's rules
+char MissingFileError::ID;
+}; // namespace reader
+}; // namespace serene
diff --git a/src/reader/reader.cpp b/src/reader/reader.cpp
index 032422c..1d3ebe9 100644
--- a/src/reader/reader.cpp
+++ b/src/reader/reader.cpp
@@ -24,49 +24,48 @@
 
 #include "serene/reader/reader.h"
 #include "serene/error.hpp"
-#include "serene/list.hpp"
-#include "serene/number.hpp"
-#include "serene/symbol.hpp"
+#include "serene/exprs/list.h"
+#include "serene/exprs/number.h"
+#include "serene/exprs/symbol.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/MemoryBuffer.h"
 
 #include <assert.h>
 #include <fstream>
-#include <iostream>
 #include <memory>
 #include <string>
 
-using namespace std;
-
 namespace serene {
 
 namespace reader {
-Reader::Reader(const string input) { this->setInput(input); };
 
-/**
- * Set the input of the reader.
- * @param input Set the input to the given string
- */
-void Reader::setInput(const string input) {
-  input_stream.write(input.c_str(), input.size());
+Reader::Reader(const llvm::StringRef input) { this->setInput(input); };
+
+/// Set the input of the reader.
+///\param input Set the input to the given string
+void Reader::setInput(const llvm::StringRef input) {
+  input_stream.write(input.str().c_str(), input.size());
 };
 
 Reader::~Reader() { READER_LOG("Destroying the reader"); }
 
-/**
- * Return the next character in the buffer.
- * @param skip_whitespace If true it will skip whitespaces and EOL chars
- */
+/// Return the next character in the buffer and moves the location.
+///\param skip_whitespace If true it will skip whitespaces and EOL chars
+/// \return next char in the buffer.
 char Reader::getChar(bool skip_whitespace) {
   for (;;) {
     char c = input_stream.get();
 
     this->current_char = c;
+
+    // TODO: Handle the end of line with respect to the OS.
+    // increase the current position in the buffer with respect to the end
+    // of line.
     inc_location(current_location, c == '\n');
 
     if (skip_whitespace == true && isspace(c)) {
-
       continue;
     } else {
       return c;
@@ -74,12 +73,15 @@ char Reader::getChar(bool skip_whitespace) {
   }
 };
 
+/// Moves back the location by one char. Basically unreads the last character.
 void Reader::ungetChar() {
   input_stream.unget();
   // The char that we just unget
   dec_location(current_location, this->current_char == '\n');
 };
 
+/// A predicate function indicating whether the given char `c` is a valid
+/// char for the starting point of a symbol or not.
 bool Reader::isValidForIdentifier(char c) {
   switch (c) {
   case '!':
@@ -110,7 +112,7 @@ bool Reader::isValidForIdentifier(char c) {
   return false;
 }
 
-ast_node Reader::readNumber(bool neg) {
+exprs::node Reader::readNumber(bool neg) {
   std::string number(neg ? "-" : "");
   bool floatNum = false;
   bool empty = false;
@@ -141,13 +143,13 @@ ast_node Reader::readNumber(bool neg) {
   if (!empty) {
     ungetChar();
     loc.end = current_location;
-    return makeNumber(loc, number, neg, floatNum);
+    return exprs::make<exprs::Number>(loc, number, neg, floatNum);
   }
 
   return nullptr;
 };
 
-ast_node Reader::readSymbol() {
+exprs::node Reader::readSymbol() {
   bool empty = true;
   char c = getChar(false);
 
@@ -186,16 +188,15 @@ ast_node Reader::readSymbol() {
   if (!empty) {
     ungetChar();
     loc.end = current_location;
-    return makeSymbol(loc, sym);
+    return exprs::make<exprs::Symbol>(loc, sym);
   }
 
   // TODO: it should never happens
   return nullptr;
 };
 
-// std::unique_ptr<List> list
-ast_list_node Reader::readList() {
-  auto list = makeList(current_location);
+exprs::node Reader::readList() {
+  auto list = exprs::makeAndCast<exprs::List>(current_location);
 
   char c = getChar(true);
   assert(c == '(');
@@ -210,7 +211,7 @@ ast_list_node Reader::readList() {
       throw ReadError(const_cast<char *>("EOF reached before closing of list"));
     case ')':
       list_terminated = true;
-      list->location->end = current_location;
+      list->location.end = current_location;
 
       break;
 
@@ -222,9 +223,9 @@ ast_list_node Reader::readList() {
   } while (!list_terminated);
 
   return list;
-}
+};
 
-ast_node Reader::readExpr() {
+exprs::node Reader::readExpr() {
   char c = getChar(false);
   READER_LOG("CHAR: " << c);
 
@@ -241,9 +242,9 @@ ast_node Reader::readExpr() {
   default:
     return readSymbol();
   }
-}
+};
 
-std::unique_ptr<ast_tree> Reader::read() {
+llvm::Expected<exprs::ast> Reader::read() {
   char c = getChar(true);
 
   while (c != EOF) {
@@ -255,18 +256,25 @@ std::unique_ptr<ast_tree> Reader::read() {
     c = getChar(true);
   }
 
-  return std::make_unique<ast_tree>(this->ast);
-}
+  return this->ast;
+};
 
 void Reader::dumpAST() {
-  ast_tree ast = *this->read();
+  auto maybeAst = read();
   std::string result = "";
-  for (auto &node : ast) {
-    result = fmt::format("{0} {1}", result, node->dumpAST());
-  }
-}
 
-std::unique_ptr<ast_tree> FileReader::read() {
+  if (!maybeAst) {
+    throw maybeAst.takeError();
+  }
+
+  exprs::ast ast = *maybeAst;
+
+  for (auto &node : ast) {
+    result = llvm::formatv("{0} {1}", result, node->toString());
+  }
+};
+
+llvm::Expected<exprs::ast> FileReader::read() {
 
   // TODO: Add support for relative path as well
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> fileOrErr =
@@ -276,7 +284,7 @@ std::unique_ptr<ast_tree> FileReader::read() {
     llvm::errs() << "Could not open input file: " << EC.message() << "\n";
     llvm::errs() << fmt::format("File: '{}'\n", file);
     llvm::errs() << "Use absolute path for now\n";
-    return nullptr;
+    return llvm::make_error<MissingFileError>(file);
   }
 
   reader->setInput(fileOrErr.get()->getBuffer().str());
@@ -285,17 +293,19 @@ std::unique_ptr<ast_tree> FileReader::read() {
 
 void FileReader::dumpAST() {
   auto maybeAst = this->read();
-  ast_tree ast;
+  exprs::ast ast;
 
-  if (maybeAst) {
-    ast = *maybeAst;
+  if (!maybeAst) {
+    throw maybeAst.takeError();
   }
 
+  ast = *maybeAst;
+
   std::string result = "";
   for (auto &node : ast) {
-    result = fmt::format("{0} {1}", result, node->dumpAST());
+    result = llvm::formatv("{0} {1}", result, node->toString());
   }
-  cout << result << endl;
+  llvm::outs() << result << "\n";
 }
 
 FileReader::~FileReader() {
diff --git a/src/sir/sir.cpp b/src/sir/sir.cpp
index 465afb9..a965910 100644
--- a/src/sir/sir.cpp
+++ b/src/sir/sir.cpp
@@ -24,7 +24,7 @@
 
 #include "serene/sir/sir.hpp"
 #include "mlir/IR/MLIRContext.h"
-#include "serene/expr.hpp"
+#include "serene/exprs/expression.h"
 #include "serene/sir/dialect.hpp"
 #include "serene/sir/generator.hpp"
 #include <memory>
@@ -41,7 +41,7 @@ mlir::OwningModuleRef SIR::generate(::serene::Namespace *ns) {
 
 SIR::~SIR() {}
 
-void dumpSIR(ast_tree &t) {
+void dumpSIR(exprs::ast &t) {
   auto ns = new ::serene::Namespace("user", llvm::None);
 
   SIR s{};
diff --git a/src/state.cpp b/src/state.cpp
index 4d05882..ffc59e4 100644
--- a/src/state.cpp
+++ b/src/state.cpp
@@ -24,7 +24,7 @@
 
 #include "serene/state.hpp"
 #include "serene/llvm/IR/Value.h"
-#include "serene/namespace.hpp"
+#include "serene/namespace.h"
 #include <fmt/core.h>
 #include <string>
 
diff --git a/src/symbol.cpp b/src/symbol.cpp
index 4c972f2..5a644c7 100644
--- a/src/symbol.cpp
+++ b/src/symbol.cpp
@@ -25,7 +25,7 @@
 #include "serene/symbol.hpp"
 #include "serene/expr.hpp"
 #include "serene/llvm/IR/Value.h"
-#include "serene/namespace.hpp"
+#include "serene/namespace.h"
 #include "serene/state.hpp"
 #include <assert.h>
 #include <fmt/core.h>
diff --git a/tests/exprs/expression_tests.cpp.inc b/tests/exprs/expression_tests.cpp.inc
index dfb6a9c..4820774 100644
--- a/tests/exprs/expression_tests.cpp.inc
+++ b/tests/exprs/expression_tests.cpp.inc
@@ -37,30 +37,9 @@ TEST_CASE("Public Expression API", "[expression]") {
 
   REQUIRE(sym->getType() == ExprType::Symbol);
   REQUIRE(sym->toString() == "<Symbol [loc: 2:20:40 | 3:30:80]: example>");
-};
 
-TEST_CASE("List Expression", "[expression]") {
-  std::unique_ptr<reader::LocationRange> range(dummyLocation());
-  auto sym = make<Symbol>(*range.get(), llvm::StringRef("example"));
+  auto list = makeAndCast<List>(*range.get(), sym);
 
-  auto list = make<List>(*range.get());
-  auto list2 = make<List>(*range.get(), list);
-  auto list3 = make<List>(*range.get(), llvm::ArrayRef<node>{list, list2, sym});
-
-  REQUIRE(list->toString() == "<List [loc: 2:20:40 | 3:30:80]: ->");
-  REQUIRE(list->getType() == ExprType::List);
-
-  REQUIRE(
-      list2->toString() ==
-      "<List [loc: 2:20:40 | 3:30:80]:  <List [loc: 2:20:40 | 3:30:80]: ->>");
-  REQUIRE(list3->toString() ==
-          "<List [loc: 2:20:40 | 3:30:80]:  <List [loc: 2:20:40 | 3:30:80]: -> "
-          "<List [loc: 2:20:40 | 3:30:80]:  <List [loc: 2:20:40 | 3:30:80]: "
-          "->> <Symbol [loc: 2:20:40 | 3:30:80]: example>>");
-
-  list->elements.push_back(sym);
-
-  REQUIRE(list->getType() == ExprType::List);
   REQUIRE(list->toString() == "<List [loc: 2:20:40 | 3:30:80]:  <Symbol [loc: "
                               "2:20:40 | 3:30:80]: example>>");
 };
diff --git a/tests/exprs/list_test.cpp b/tests/exprs/list_test.cpp
new file mode 100644
index 0000000..8a06f8a
--- /dev/null
+++ b/tests/exprs/list_test.cpp
@@ -0,0 +1,61 @@
+/* -*- C++ -*-
+ * Serene programming language.
+ *
+ *  Copyright (c) 2019-2021 Sameer Rahmani <lxsameer@gnu.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "../test_helpers.cpp.inc"
+#include "serene/exprs/list.h"
+#include "serene/exprs/symbol.h"
+
+namespace serene {
+namespace exprs {
+
+TEST_CASE("List Expression", "[expression]") {
+  std::unique_ptr<reader::LocationRange> range(dummyLocation());
+
+  auto sym = make<Symbol>(*range.get(), llvm::StringRef("example"));
+  auto list = make<List>(*range.get());
+  auto list2 = make<List>(*range.get(), list);
+  auto list3 = make<List>(*range.get(), llvm::ArrayRef<node>{list, list2, sym});
+
+  REQUIRE(list->toString() == "<List [loc: 2:20:40 | 3:30:80]: ->");
+  REQUIRE(list->getType() == ExprType::List);
+
+  REQUIRE(
+      list2->toString() ==
+      "<List [loc: 2:20:40 | 3:30:80]:  <List [loc: 2:20:40 | 3:30:80]: ->>");
+  REQUIRE(list3->toString() ==
+          "<List [loc: 2:20:40 | 3:30:80]:  <List [loc: 2:20:40 | 3:30:80]: -> "
+          "<List [loc: 2:20:40 | 3:30:80]:  <List [loc: 2:20:40 | 3:30:80]: "
+          "->> <Symbol [loc: 2:20:40 | 3:30:80]: example>>");
+
+  auto l = llvm::dyn_cast<List>(list);
+
+  l.append(sym);
+
+  REQUIRE(list->getType() == ExprType::List);
+  REQUIRE(list->toString() == "<List [loc: 2:20:40 | 3:30:80]:  <Symbol [loc: "
+                              "2:20:40 | 3:30:80]: example>>");
+};
+
+} // namespace exprs
+} // namespace serene