diff --git a/bin/serene.cpp b/bin/serene.cpp
index 9b8ddbf..26a272d 100644
--- a/bin/serene.cpp
+++ b/bin/serene.cpp
@@ -22,7 +22,7 @@
  * SOFTWARE.
  */
 
-#include "serene/serene.hpp"
+#include "serene/serene.h"
 #include "serene/reader/reader.hpp"
 #include "serene/sir/sir.hpp"
 #include <iostream>
diff --git a/include/serene/exprs/expression.h b/include/serene/exprs/expression.h
new file mode 100644
index 0000000..4916eb9
--- /dev/null
+++ b/include/serene/exprs/expression.h
@@ -0,0 +1,69 @@
+/* -*- 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_EXPRESSION_H
+#define EXPRS_EXPRESSION_H
+
+#include <memory>
+
+namespace serene {
+
+/// Contains all the builtin expressions including those which do not appear in
+/// the syntax directly. Like function definitions.
+namespace exprs {
+
+/// 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**
+class Expression {
+public:
+  template <typename T>
+  Expression(T e) : self(new ExpressionImpl<T>(std::move(e))){};
+
+private:
+  /// The generic interface which each type of expression has to implement
+  /// in order to act like an `Expression`
+  struct ExpressionConcept {
+    virtual ~ExpressionConcept() = default;
+    virtual ExpressionConcept *copy_() const = 0;
+  };
+
+  /// The generic implementation of `ExpressionConcept` which acts as the
+  /// dispatcher on type.
+  template <typename T> struct ExpressionImpl : ExpressionConcept {
+    ExpressionImpl(T e) : expr(std::move(e)){};
+    ExpressionConcept *copy_() const { return new ExpressionImpl(*this); }
+
+    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;
+};
+
+} // namespace exprs
+} // namespace serene
+
+#endif
diff --git a/include/serene/exprs/list.h b/include/serene/exprs/list.h
new file mode 100644
index 0000000..d0a338e
--- /dev/null
+++ b/include/serene/exprs/list.h
@@ -0,0 +1,43 @@
+/* -*- 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_SYMBOL_H
+#define EXPRS_SYMBOL_H
+
+#include "serene/exprs/expression.h"
+#include "llvm/ADT/SmallVector.h"
+#include <string>
+
+namespace serene {
+
+namespace exprs {
+
+struct List {
+  llvm::SmallVector<Expression, 0> elements;
+};
+
+} // namespace exprs
+} // namespace serene
+
+#endif
diff --git a/include/serene/exprs/symbol.h b/include/serene/exprs/symbol.h
new file mode 100644
index 0000000..aadfa3b
--- /dev/null
+++ b/include/serene/exprs/symbol.h
@@ -0,0 +1,41 @@
+/* -*- 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_SYMBOL_H
+#define EXPRS_SYMBOL_H
+
+#include <string>
+
+namespace serene {
+
+namespace exprs {
+
+struct Symbol {
+  std::string name;
+};
+
+} // namespace exprs
+} // namespace serene
+
+#endif
diff --git a/include/serene/reader/reader.hpp b/include/serene/reader/reader.hpp
index 1908921..7e369b7 100644
--- a/include/serene/reader/reader.hpp
+++ b/include/serene/reader/reader.hpp
@@ -37,7 +37,7 @@
 #include "serene/list.hpp"
 #include "serene/logger.hpp"
 #include "serene/reader/location.hpp"
-#include "serene/serene.hpp"
+#include "serene/serene.h"
 #include "serene/symbol.hpp"
 
 #if defined(ENABLE_READER_LOG) || defined(ENABLE_LOG)
diff --git a/include/serene/serene.hpp b/include/serene/serene.h
similarity index 95%
rename from include/serene/serene.hpp
rename to include/serene/serene.h
index 6003ca7..3a13f2b 100644
--- a/include/serene/serene.hpp
+++ b/include/serene/serene.h
@@ -1,7 +1,7 @@
-/**
+/*
  * Serene programming language.
  *
- *  Copyright (c) 2020 Sameer Rahmani <lxsameer@gnu.org>
+ *  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
diff --git a/include/serene/sir/generator.hpp b/include/serene/sir/generator.hpp
index cb91504..fe913f4 100644
--- a/include/serene/sir/generator.hpp
+++ b/include/serene/sir/generator.hpp
@@ -55,8 +55,8 @@ private:
   // TODO: Should we use builder here? maybe there is a better option
   ::mlir::Location toMLIRLocation(serene::reader::Location *);
 
-  mlir::FuncOp generateFn(serene::reader::Location, std::string, List *,
-                          List *);
+  // mlir::FuncOp generateFn(serene::reader::Location, std::string, List *,
+  //                         List *);
 
 public:
   Generator(mlir::MLIRContext &context, ::serene::Namespace *ns)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3f06a34..f9b77c6 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,6 +1,14 @@
 set(HEADER_LIST
+  "${INCLUDE_DIR}/serene/serene.h"
+
+  "${INCLUDE_DIR}/serene/exprs/expression.h"
+  "${INCLUDE_DIR}/serene/exprs/symbol.h"
+  "${INCLUDE_DIR}/serene/exprs/list.h"
+
+
+
   "${INCLUDE_DIR}/serene/expr.hpp"
-  "${INCLUDE_DIR}/serene/serene.hpp"
+
   "${INCLUDE_DIR}/serene/number.hpp"
   "${INCLUDE_DIR}/serene/symbol.hpp"
   "${INCLUDE_DIR}/serene/list.hpp"
@@ -19,6 +27,9 @@ set(HEADER_LIST
 
 # Make an automatic library - will be static or dynamic based on user setting
 add_library(serene
+  exprs/symbol.cpp
+  exprs/list.cpp
+
   serene.cpp
   symbol.cpp
   list.cpp
diff --git a/src/exprs/list.cpp b/src/exprs/list.cpp
new file mode 100644
index 0000000..0fda9d8
--- /dev/null
+++ b/src/exprs/list.cpp
@@ -0,0 +1,25 @@
+/*
+ * 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/list.h"
diff --git a/src/exprs/symbol.cpp b/src/exprs/symbol.cpp
new file mode 100644
index 0000000..ed0739c
--- /dev/null
+++ b/src/exprs/symbol.cpp
@@ -0,0 +1,25 @@
+/*
+ * 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/symbol.h"
diff --git a/src/serene.cpp b/src/serene.cpp
index 196c3d8..c0e58e4 100644
--- a/src/serene.cpp
+++ b/src/serene.cpp
@@ -22,6 +22,6 @@
  * SOFTWARE.
  */
 
-#include "serene/serene.hpp"
+#include "serene/serene.h"
 #include "serene/reader/reader.hpp"
 #include <iostream>
diff --git a/src/sir/generator.cpp b/src/sir/generator.cpp
index 3f22b15..2bee14e 100644
--- a/src/sir/generator.cpp
+++ b/src/sir/generator.cpp
@@ -40,139 +40,144 @@ namespace serene {
 namespace sir {
 
 mlir::ModuleOp Generator::generate() {
-  for (auto x : ns->Tree()) {
-    generate(x.get());
-  }
+  // for (auto x : ns->Tree()) {
+  //   generate(x.get());
+  // }
 
   return module;
 };
 
 mlir::Operation *Generator::generate(AExpr *x) {
-  switch (x->getType()) {
-  case SereneType::Number: {
-    return generate(llvm::cast<Number>(x));
-  }
+  // switch (x->getType()) {
+  // case SereneType::Number: {
+  //   return generate(llvm::cast<Number>(x));
+  // }
 
-  case SereneType::List: {
-    generate(llvm::cast<List>(x));
-    return nullptr;
-  }
+  // case SereneType::List: {
+  //   generate(llvm::cast<List>(x));
+  //   return nullptr;
+  // }
 
-  default: {
-    return builder.create<ValueOp>(builder.getUnknownLoc(), (uint64_t)3);
-  }
-  }
+  // default: {
+  return builder.create<ValueOp>(builder.getUnknownLoc(), (uint64_t)3);
+  // }
+  // }
 };
 
 mlir::Value Generator::generate(List *l) {
-  auto first = l->at(0);
+  // auto first = l->at(0);
 
-  if (!first) {
-    // Empty list.
-    // TODO: Return Nil or empty list.
+  // if (!first) {
+  //   // Empty list.
+  //   // TODO: Return Nil or empty list.
 
-    // Just for now.
-    return builder.create<ValueOp>(builder.getUnknownLoc(), (uint64_t)0);
-  }
-
-  if (first->get()->getType() == SereneType::Symbol) {
-    auto fnNameSymbol = llvm::dyn_cast<Symbol>(first->get());
-
-    if (fnNameSymbol->getName() == "fn") {
-      if (l->count() <= 3) {
-        module.emitError("'fn' form needs exactly 2 arguments.");
-      }
-
-      auto args = llvm::dyn_cast<List>(l->at(1).getValue().get());
-      auto body = llvm::dyn_cast<List>(l->from(2).get());
-
-      if (!args) {
-        module.emitError("The first element of 'def' has to be a symbol.");
-      }
-
-      // Create a new anonymous function and push it to the anonymous functions
-      // map, later on we
-      auto loc(fnNameSymbol->location->start);
-      auto anonymousName = fmt::format("__fn_{}__", anonymousFnCounter);
-      anonymousFnCounter++;
-
-      auto fn = generateFn(loc, anonymousName, args, body);
-      mlir::Identifier fnid = builder.getIdentifier(anonymousName);
-      anonymousFunctions.insert({fnid, fn});
-      return builder.create<FnIdOp>(builder.getUnknownLoc(), fnid.str());
-    }
-  }
-  // auto rest = l->from(1);
-  // auto loc = toMLIRLocation(&first->get()->location->start);
-  // for (auto x : *rest) {
-  //   generate(x.get());
+  //   // Just for now.
+  //   return builder.create<ValueOp>(builder.getUnknownLoc(), (uint64_t)0);
   // }
 
+  // if (first->get()->getType() == SereneType::Symbol) {
+  //   auto fnNameSymbol = llvm::dyn_cast<Symbol>(first->get());
+
+  //   if (fnNameSymbol->getName() == "fn") {
+  //     if (l->count() <= 3) {
+  //       module.emitError("'fn' form needs exactly 2 arguments.");
+  //     }
+
+  //     auto args = llvm::dyn_cast<List>(l->at(1).getValue().get());
+  //     auto body = llvm::dyn_cast<List>(l->from(2).get());
+
+  //     if (!args) {
+  //       module.emitError("The first element of 'def' has to be a symbol.");
+  //     }
+
+  //     // Create a new anonymous function and push it to the anonymous
+  //     functions
+  //     // map, later on we
+  //     auto loc(fnNameSymbol->location->start);
+  //     auto anonymousName = fmt::format("__fn_{}__", anonymousFnCounter);
+  //     anonymousFnCounter++;
+
+  //     auto fn = generateFn(loc, anonymousName, args, body);
+  //     mlir::Identifier fnid = builder.getIdentifier(anonymousName);
+  //     anonymousFunctions.insert({fnid, fn});
+  //     return builder.create<FnIdOp>(builder.getUnknownLoc(), fnid.str());
+  //   }
+  // }
+  // // auto rest = l->from(1);
+  // // auto loc = toMLIRLocation(&first->get()->location->start);
+  // // for (auto x : *rest) {
+  // //   generate(x.get());
+  // // }
+
   return builder.create<ValueOp>(builder.getUnknownLoc(), (uint64_t)100);
 };
 
-mlir::FuncOp Generator::generateFn(serene::reader::Location loc,
-                                   std::string name, List *args, List *body) {
+// mlir::FuncOp Generator::generateFn(serene::reader::Location loc,
+//                                    std::string name, List *args, List *body)
+//                                    {
 
-  auto location = toMLIRLocation(&loc);
-  llvm::SmallVector<mlir::Type, 4> arg_types(args->count(),
-                                             builder.getI64Type());
-  auto func_type = builder.getFunctionType(arg_types, builder.getI64Type());
-  auto proto = mlir::FuncOp::create(location, name, func_type);
-  mlir::FuncOp fn(proto);
+//   auto location = toMLIRLocation(&loc);
+//   llvm::SmallVector<mlir::Type, 4> arg_types(args->count(),
+//                                              builder.getI64Type());
+//   auto func_type = builder.getFunctionType(arg_types, builder.getI64Type());
+//   auto proto = mlir::FuncOp::create(location, name, func_type);
+//   mlir::FuncOp fn(proto);
 
-  if (!fn) {
-    module.emitError("Can not create the function.");
-  }
+//   if (!fn) {
+//     module.emitError("Can not create the function.");
+//   }
 
-  auto &entryBlock = *fn.addEntryBlock();
-  llvm::ScopedHashTableScope<llvm::StringRef, mlir::Value> scope(symbolTable);
+//   auto &entryBlock = *fn.addEntryBlock();
+//   llvm::ScopedHashTableScope<llvm::StringRef, mlir::Value>
+//   scope(symbolTable);
 
-  // Declare all the function arguments in the symbol table.
-  for (const auto arg :
-       llvm::zip(args->asArrayRef(), entryBlock.getArguments())) {
+//   // Declare all the function arguments in the symbol table.
+//   for (const auto arg :
+//        llvm::zip(args->asArrayRef(), entryBlock.getArguments())) {
 
-    auto argSymbol = llvm::dyn_cast<Symbol>(std::get<0>(arg).get());
-    if (!argSymbol) {
-      module.emitError("Function parameters must be symbols");
-    }
-    if (symbolTable.count(argSymbol->getName())) {
-      return nullptr;
-    }
-    symbolTable.insert(argSymbol->getName(), std::get<1>(arg));
-  }
+//     auto argSymbol = llvm::dyn_cast<Symbol>(std::get<0>(arg).get());
+//     if (!argSymbol) {
+//       module.emitError("Function parameters must be symbols");
+//     }
+//     if (symbolTable.count(argSymbol->getName())) {
+//       return nullptr;
+//     }
+//     symbolTable.insert(argSymbol->getName(), std::get<1>(arg));
+//   }
 
-  // Set the insertion point in the builder to the beginning of the function
-  // body, it will be used throughout the codegen to create operations in this
-  // function.
-  builder.setInsertionPointToStart(&entryBlock);
+//   // Set the insertion point in the builder to the beginning of the function
+//   // body, it will be used throughout the codegen to create operations in
+//   this
+//   // function.
+//   builder.setInsertionPointToStart(&entryBlock);
 
-  // Emit the body of the function.
-  if (!generate(body)) {
-    fn.erase();
-    return nullptr;
-  }
+//   // Emit the body of the function.
+//   if (!generate(body)) {
+//     fn.erase();
+//     return nullptr;
+//   }
 
-  // // Implicitly return void if no return statement was emitted.
-  // // FIXME: we may fix the parser instead to always return the last
-  // expression
-  // // (this would possibly help the REPL case later)
-  // ReturnOp returnOp;
+//   // // Implicitly return void if no return statement was emitted.
+//   // // FIXME: we may fix the parser instead to always return the last
+//   // expression
+//   // // (this would possibly help the REPL case later)
+//   // ReturnOp returnOp;
 
-  // if (!entryBlock.empty())
-  //   returnOp = dyn_cast<ReturnOp>(entryBlock.back());
-  // if (!returnOp) {
-  //   builder.create<ReturnOp>(loc(funcAST.getProto()->loc()));
-  // } else if (returnOp.hasOperand()) {
-  //   // Otherwise, if this return operation has an operand then add a result
-  //   to
-  //   // the function.
-  //   function.setType(builder.getFunctionType(function.getType().getInputs(),
-  //                                            getType(VarType{})));
-  // }
+//   // if (!entryBlock.empty())
+//   //   returnOp = dyn_cast<ReturnOp>(entryBlock.back());
+//   // if (!returnOp) {
+//   //   builder.create<ReturnOp>(loc(funcAST.getProto()->loc()));
+//   // } else if (returnOp.hasOperand()) {
+//   //   // Otherwise, if this return operation has an operand then add a
+//   result
+//   //   to
+//   //   // the function.
+//   // function.setType(builder.getFunctionType(function.getType().getInputs(),
+//   //                                            getType(VarType{})));
+//   // }
 
-  return fn;
-}
+//   return fn;
+// }
 
 mlir::Operation *Generator::generate(Number *x) {
   return builder.create<ValueOp>(builder.getUnknownLoc(), x->toI64());