diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9df12bb..96bc99e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,7 +4,7 @@ project(RiDDLe VERSION 0.2.0 LANGUAGES C CXX)
 include(CTest)
 enable_testing()
 
-add_library(RiDDLe src/scope.cpp src/env.cpp src/core.cpp src/type.cpp src/constructor.cpp src/method.cpp src/item.cpp)
+add_library(RiDDLe src/scope.cpp src/env.cpp src/core.cpp src/type.cpp src/constructor.cpp src/method.cpp src/conjunction.cpp src/item.cpp src/expression.cpp)
 target_include_directories(RiDDLe PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>)
 
 set(CPACK_PROJECT_NAME ${PROJECT_NAME})
diff --git a/include/conjunction.hpp b/include/conjunction.hpp
new file mode 100644
index 0000000..f5d093a
--- /dev/null
+++ b/include/conjunction.hpp
@@ -0,0 +1,16 @@
+#pragma once
+
+#include "scope.hpp"
+#include "env.hpp"
+
+namespace riddle
+{
+  class conjunction : public scope
+  {
+  public:
+    conjunction(std::shared_ptr<scope> parent, std::shared_ptr<env> ctx);
+
+  private:
+    std::shared_ptr<env> ctx;
+  };
+} // namespace riddle
diff --git a/include/core.hpp b/include/core.hpp
index 84e8044..2d7c208 100644
--- a/include/core.hpp
+++ b/include/core.hpp
@@ -11,6 +11,20 @@ namespace riddle
     core();
     virtual ~core() = default;
 
+    /**
+     * @brief Create a new bool expression.
+     *
+     * @return std::shared_ptr<item> The bool expression.
+     */
+    virtual std::shared_ptr<item> new_bool() = 0;
+    /**
+     * @brief Create a new bool expression with a value.
+     *
+     * @param value The value of the bool expression.
+     * @return std::shared_ptr<item> The bool expression.
+     */
+    virtual std::shared_ptr<item> new_bool(bool value) = 0;
+
     /**
      * @brief Get a field by name.
      *
diff --git a/include/expression.hpp b/include/expression.hpp
new file mode 100644
index 0000000..8a1209f
--- /dev/null
+++ b/include/expression.hpp
@@ -0,0 +1,29 @@
+#pragma once
+
+#include "item.hpp"
+#include "lexer.hpp"
+
+namespace riddle
+{
+  class scope;
+
+  class expression
+  {
+  public:
+    expression() = default;
+    virtual ~expression() = default;
+
+    virtual std::shared_ptr<item> evaluate(scope &scp, env &ctx) = 0;
+  };
+
+  class bool_expression final : public expression
+  {
+  public:
+    bool_expression(const bool_token &l) : l(l) {}
+
+    std::shared_ptr<item> evaluate(scope &scp, env &ctx) override;
+
+  private:
+    bool_token l;
+  };
+} // namespace riddle
diff --git a/include/lexer.hpp b/include/lexer.hpp
new file mode 100644
index 0000000..485111e
--- /dev/null
+++ b/include/lexer.hpp
@@ -0,0 +1,82 @@
+#pragma once
+
+#include <cstddef>
+
+namespace riddle
+{
+  enum symbol
+  {
+    BOOL_ID,          // `bool`
+    INT_ID,           // `int`
+    REAL_ID,          // `real`
+    TIME_ID,          // `time`
+    STRING_ID,        // `string`
+    TYPEDEF_ID,       // `typedef`
+    ENUM_ID,          // `enum`
+    CLASS_ID,         // `class`
+    GOAL_ID,          // `goal`
+    FACT_ID,          // `fact`
+    PREDICATE_ID,     // `predicate`
+    NEW_ID,           // `new`
+    OR_ID,            // `or`
+    FOR_ID,           // `for`
+    THIS_ID,          // `this`
+    VOID_ID,          // `void`
+    RETURN_ID,        // `return`
+    DOT_ID,           // `.`
+    COMMA_ID,         // `,`
+    COLON_ID,         // `:`
+    SEMICOLON_ID,     // `;`
+    LPAREN_ID,        // `(`
+    RPAREN_ID,        // `)`
+    LBRACKET_ID,      // `[`
+    RBRACKET_ID,      // `]`
+    LBRACE_ID,        // `{`
+    RBRACE_ID,        // `}`
+    PLUS_ID,          // `+`
+    MINUS_ID,         // `-`
+    STAR_ID,          // `*`
+    SLASH_ID,         // `/`
+    AMP_ID,           // `&`
+    BAR_ID,           // `|`
+    EQ_ID,            // `=`
+    GT_ID,            // `>`
+    LT_ID,            // `<`
+    BANG_ID,          // `!`
+    EQEQ_ID,          // `==`
+    LTEQ_ID,          // `<=`
+    GTEQ_ID,          // `>=`
+    BANGEQ_ID,        // `!=`
+    IMPLICATION_ID,   // `->`
+    CARET_ID,         // `^`
+    ID_ID,            // (`a`..`z`|`A`..`Z`|`_`) (`a`..`z`|`A`..`Z`|`0`..`9`|`_`)*
+    BoolLiteral_ID,   // `true` | `false`
+    IntLiteral_ID,    // [0-9]+
+    RealLiteral_ID,   // [0-9]+ `.` [0-9]+)? | `.` [0-9]+
+    StringLiteral_ID, // `" . . ."`
+    EOF_ID
+  };
+
+  class token
+  {
+  public:
+    token(const symbol &sym, const size_t &start_line, const size_t &start_pos, const size_t &end_line, const size_t &end_pos) : sym(sym), start_line(start_line), start_pos(start_pos), end_line(end_line), end_pos(end_pos) {}
+    virtual ~token() = default;
+
+    const symbol sym;
+    const size_t start_line, start_pos, end_line, end_pos;
+  };
+
+  class bool_token final : public token
+  {
+  public:
+    bool_token(const bool &value, const size_t &start_line, const size_t &start_pos, const size_t &end_line, const size_t &end_pos) : token(BOOL_ID, start_line, start_pos, end_line, end_pos), value(value) {}
+    virtual ~bool_token() = default;
+
+    const bool value;
+  };
+
+  class lexer
+  {
+  };
+} // namespace riddle
diff --git a/src/conjunction.cpp b/src/conjunction.cpp
new file mode 100644
index 0000000..7f5fdb7
--- /dev/null
+++ b/src/conjunction.cpp
@@ -0,0 +1,6 @@
+#include "conjunction.hpp"
+
+namespace riddle
+{
+    conjunction::conjunction(std::shared_ptr<scope> parent, std::shared_ptr<env> ctx) : scope(parent->get_core(), parent), ctx(ctx) {}
+} // namespace riddle
\ No newline at end of file
diff --git a/src/expression.cpp b/src/expression.cpp
new file mode 100644
index 0000000..119ed59
--- /dev/null
+++ b/src/expression.cpp
@@ -0,0 +1,7 @@
+#include "expression.hpp"
+#include "core.hpp"
+
+namespace riddle
+{
+    std::shared_ptr<item> bool_expression::evaluate(scope &scp, env &ctx) { return scp.get_core().new_bool(l.value); }
+} // namespace riddle