diff --git a/include/ast/decl.hh b/include/ast/decl.hh
index 1739948..332c715 100644
--- a/include/ast/decl.hh
+++ b/include/ast/decl.hh
@@ -50,7 +50,7 @@ namespace rift
         class DeclVar: public Decl
         {
             public:
-                DeclVar(const Token&identifier): identifier(identifier), expr(nullptr) {};
+                DeclVar(const Token &identifier): identifier(identifier), expr(nullptr) {};
                 DeclVar(const Token &identifier, std::unique_ptr<Expr> expr): identifier(identifier), expr(std::move(expr)) {};
                 Tokens accept(const Visitor &visitor) const override { return visitor.visit_decl_var(*this); }
 
diff --git a/include/ast/env.hh b/include/ast/env.hh
index 7d73dcb..61f41ec 100644
--- a/include/ast/env.hh
+++ b/include/ast/env.hh
@@ -17,6 +17,7 @@
 // #include <absl/container/flat_hash_map.h>
 #include <scanner/tokens.hh>
 #include <unordered_map>
+#include <unordered_set>
 #include <iostream>
 
 using Token = rift::scanner::Token;
@@ -71,12 +72,13 @@ namespace rift
                 Environment(Environment *child) : child(child) {}
                 ~Environment() = default;
                 Token getEnv(const str_t& name) const;
-                void setEnv(const str_t& name, const Token& value);
+                void setEnv(const str_t& name, const Token& value, bool is_const);
                 void printState();
                 Environment *child;
             protected:
                 // absl::flat_hash_map<str_t, rift::scanner::Token> values;
                 std::unordered_map<str_t, rift::scanner::Token> values = {};
+                std::unordered_set<str_t> const_keys = {};
         };
     }
 }
\ No newline at end of file
diff --git a/include/ast/parser.hh b/include/ast/parser.hh
index f01b507..9887a24 100644
--- a/include/ast/parser.hh
+++ b/include/ast/parser.hh
@@ -85,8 +85,8 @@ namespace rift
                 /// @note rules in order of precedence <Decl>
                 /// @example var x = 1;
                 std::unique_ptr<DeclStmt> declaration_statement();
-                /// @example var x = 1;
-                std::unique_ptr<DeclVar> declaration_variable();
+                /// @example mut x = 1; mut! x = 5;
+                std::unique_ptr<DeclVar> declaration_variable(bool mut);
 
                 /// @example while(true) print("hi");
                 std::unique_ptr<For> for_();
@@ -100,6 +100,8 @@ namespace rift
                 void synchronize();
                 /// @brief returns any statements that might be executed 
                 std::unique_ptr<Stmt> ret_stmt();
+                /// @brief returns any declarations that might be executed
+                vec_prog ret_decl();
         };
 
         class ParserException : public ReaderException
diff --git a/include/scanner/scanner.hh b/include/scanner/scanner.hh
index a78caa5..1ecdc66 100644
--- a/include/scanner/scanner.hh
+++ b/include/scanner/scanner.hh
@@ -21,7 +21,7 @@
 #include <stdlib.h>
 // #include <map>
 
-#include <unordered_map>
+#include <map>
 #include <vector>
 
 using namespace rift::reader;
@@ -37,7 +37,7 @@ namespace rift
         {
             std::shared_ptr<std::vector<char>> source;
             std::vector<Token> tokens;
-            std::unordered_map<std::string, Type> keywords;
+            std::map<str_t, Type, std::greater<str_t> > keywords;
 
             Scanner(std::shared_ptr<std::vector<char>> source);
             ~Scanner(){}
diff --git a/include/scanner/tokens.hh b/include/scanner/tokens.hh
index d46b785..98c6500 100644
--- a/include/scanner/tokens.hh
+++ b/include/scanner/tokens.hh
@@ -62,6 +62,7 @@ namespace rift
 
             // Literals
             IDENTIFIER,
+            C_IDENTIFIER,
             STRINGLITERAL,
             NUMERICLITERAL,
 
@@ -80,6 +81,7 @@ namespace rift
             THIS,
             TRUE,
             VAR,
+            CONST,
             WHILE,
             
             IGNORE,
@@ -130,7 +132,7 @@ namespace rift
                 << ", Line=" << token.line << ")"*/;
                 return os;
             }
-            bool operator==(const Token &token);
+            bool operator==(const Token &token) const;
 
             std::any getLiteral() const;
         };
diff --git a/lib/ast/env.cc b/lib/ast/env.cc
index 94d8599..79d9401 100644
--- a/lib/ast/env.cc
+++ b/lib/ast/env.cc
@@ -31,12 +31,17 @@ namespace rift
             return values.at(name);
         }
 
-        void Environment::setEnv(const str_t& name, const Token& value)
+        void Environment::setEnv(const str_t& name, const Token& value, bool is_const)
         {
             if (!values.contains(name) && child != nullptr) {
-                child->setEnv(name, value);
+                child->setEnv(name, value, is_const);
             } else {
-                values[name] = value;
+                if (values.contains(name) && const_keys.contains(name)) {
+                    error::report(0, "Environment", "Cannot reassign a constant variable", values.at(name), std::exception());
+                } else {
+                    values[name] = value;
+                    if (is_const) const_keys.insert(name);
+                }
             }
         }
 
diff --git a/lib/ast/eval.cc b/lib/ast/eval.cc
index 3a10c94..216f5c9 100644
--- a/lib/ast/eval.cc
+++ b/lib/ast/eval.cc
@@ -112,7 +112,7 @@ namespace rift
         Token Visitor::visit_assign(const Assign& expr) const
         {
             auto name = castString(expr.name);
-            env::getInstance().setEnv(name, expr.value->accept(*this));
+            env::getInstance().setEnv(name, expr.value->accept(*this), expr.name.type == TokenType::C_IDENTIFIER);
             return env::getInstance().getEnv(name);;
         }
 
@@ -363,7 +363,7 @@ namespace rift
                 toks.push_back(decl.expr->accept(*this));
             } else {
                 auto niltok = Token(TokenType::NIL, "null", nullptr, decl.identifier.line);
-                env::getInstance().setEnv(decl.identifier.lexeme, niltok);
+                env::getInstance().setEnv(decl.identifier.lexeme, niltok, decl.identifier.type == TokenType::C_IDENTIFIER);
                 toks.push_back(niltok);
             }
             return toks;
diff --git a/lib/ast/parser.cc b/lib/ast/parser.cc
index 1eee5fb..7fc2883 100644
--- a/lib/ast/parser.cc
+++ b/lib/ast/parser.cc
@@ -295,9 +295,10 @@ namespace rift
             return std::make_unique<DeclStmt>(std::move(stmt));
         }
 
-        std::unique_ptr<DeclVar> Parser::declaration_variable()
+        std::unique_ptr<DeclVar> Parser::declaration_variable(bool mut)
         {
             // make sure there is an identifier
+            auto tok_t = mut ? TokenType::IDENTIFIER : TokenType::C_IDENTIFIER;
             auto idt = consume(Token(TokenType::IDENTIFIER, "", "", line), std::unique_ptr<ParserException>(new ParserException("Expected variable name")));
             prevance();
             // make sure the identifier is not already declared
@@ -305,18 +306,20 @@ namespace rift
             ///       this also checks if any outer block has already declared this variable
             if (env::getInstance().getEnv(castString(idt)) != Token())
                 rift::error::report(line, "declaration_variable", "🛑 Variable '" + castString(idt) + "' already declared at line: " + castNumberString(idt.line), idt, ParserException("Variable '" + castString(idt) + "' already declared"));
-            env::getInstance().setEnv(castString(idt), idt);
+            env::getInstance().setEnv(castString(idt), idt, idt.type == TokenType::C_IDENTIFIER);
 
             if(peekNext() == Token(TokenType::EQUAL, "=", "", line)) {
                 auto expr = assignment();
                 consume(Token(TokenType::SEMICOLON, ";", "", line), std::unique_ptr<ParserException>(new ParserException("Expected ';' after variable assignment")));
+                idt.type = tok_t;
                 return std::make_unique<DeclVar>(idt, std::move(expr));
+            } else if (!mut) {
+                rift::error::report(line, "declaration_variable", "🛑 Constants must be defined", idt, ParserException("Constants must be defined"));
             }
 
             idt = consume(Token(TokenType::IDENTIFIER, "", "", line), std::unique_ptr<ParserException>(new ParserException("Expected variable name")));
             consume(Token(TokenType::SEMICOLON, ";", "", line), std::unique_ptr<ParserException>(new ParserException("Expected ';' after variable declaration")));
-            // return std::make_unique<DeclVar>(idt, std::unique_ptr<Literal>(new Literal(Token(TokenType::NIL, "nil", "", line))));
-            return std::make_unique<DeclVar>(idt);
+            return std::unique_ptr<DeclVar>(new DeclVar(Token(tok_t, idt.lexeme, idt.literal, idt.line)));
         }
 
         std::unique_ptr<For> Parser::for_()
@@ -326,7 +329,9 @@ namespace rift
 
             // first ;
             if (match({Token(TokenType::VAR, "", "", line)})) {
-                _for->decl = std::move(declaration_variable());
+                _for->decl = std::move(declaration_variable(true));
+            } else if (match({Token(TokenType::CONST, "", "", line)}))  {
+                _for->decl = std::move(declaration_variable(false));
             } else if(peek(Token(TokenType::IDENTIFIER, "", "", line))) {
                 _for->stmt_l = std::move(ret_stmt());
             }
@@ -339,9 +344,8 @@ namespace rift
             consume(Token(TokenType::SEMICOLON, ";", "", line), std::unique_ptr<ParserException>(new ParserException("Expected ';' after for second statement")));
 
             // third ;
-            if(peek(Token(TokenType::IDENTIFIER, "", "", line))) {
+            if(peek(Token(TokenType::IDENTIFIER, "", "", line)))
                 _for->stmt_r = std::move(ret_stmt());
-            }
             consume(Token(TokenType::RIGHT_PAREN, ")", "", line), std::unique_ptr<ParserException>(new ParserException("Expected ')' after for")));
 
             if (match({Token(TokenType::LEFT_BRACE, "{", "", line)})) {
@@ -355,21 +359,34 @@ namespace rift
 
         #pragma mark - Program / Block Parsing
 
+        vec_prog Parser::ret_decl()
+        {
+            vec_prog decls = std::make_unique<std::vector<std::unique_ptr<Decl>>>();
+            if (consume (Token(TokenType::VAR, "", "", line))) {
+                auto test = declaration_variable(true);
+                decls->emplace_back(std::move(test));
+            } else if (consume (Token(TokenType::CONST, "", "", line))) {
+                auto test = declaration_variable(false);
+                decls->emplace_back(std::move(test));
+            } else if (consume (Token(TokenType::FOR, "", "", line)))  {
+                decls->emplace_back(for_());
+            } else if(match({Token(TokenType::LEFT_BRACE, "{", "", line)})) {
+                auto inner_decls = std::move(block()->decls);
+                decls->insert(decls->end(), std::make_move_iterator(inner_decls->begin()), std::make_move_iterator(inner_decls->end()));
+            } else {
+                decls->emplace_back(declaration_statement());
+            }
+            return decls;
+        }
+
         std::unique_ptr<Block> Parser::block()
         {
             vec_prog decls = std::make_unique<std::vector<std::unique_ptr<Decl>>>();
 
             env::addChild();
             while (!atEnd() && !peek(Token(TokenType::RIGHT_BRACE, "}", "", line))) {
-                if (match({Token(TokenType::LEFT_BRACE, "{", "", line)})) {
-                    auto inner_decls = std::move(block()->decls);
-                    decls->insert(decls->end(), std::make_move_iterator(inner_decls->begin()), std::make_move_iterator(inner_decls->end()));
-                } else if (consume (Token(TokenType::VAR, "", "", line))) {
-                    auto decl = declaration_variable();
-                    decls->push_back(std::move(decl));
-                } else {
-                    decls->push_back(declaration_statement());
-                }
+                auto inner = ret_decl();
+                decls->insert(decls->end(), std::make_move_iterator(inner->begin()), std::make_move_iterator(inner->end()));
             }
             env::removeChild();
 
@@ -384,16 +401,8 @@ namespace rift
             vec_prog decls = std::make_unique<std::vector<std::unique_ptr<Decl>>>();
 
             while (!atEnd()) {
-                if (consume (Token(TokenType::VAR, "", "", line))) {
-                    auto test = declaration_variable();
-                    decls->emplace_back(std::move(test)); // GIVING ME UB
-                } else if (consume (Token(TokenType::FOR, "", "", line)))  {
-                    decls->push_back(for_());
-                } else if(match({Token(TokenType::LEFT_BRACE, "{", "", line)})) {
-                    decls->push_back(block());
-                } else {
-                    decls->push_back(declaration_statement());
-                }
+                auto inner = ret_decl();
+                decls->insert(decls->end(), std::make_move_iterator(inner->begin()), std::make_move_iterator(inner->end()));
             }
 
             return std::unique_ptr<Program>(new Program(std::move(decls)));
diff --git a/lib/scanner/scanner.cc b/lib/scanner/scanner.cc
index a56876a..553a8d9 100644
--- a/lib/scanner/scanner.cc
+++ b/lib/scanner/scanner.cc
@@ -32,7 +32,7 @@ namespace rift
             this->source = source;
             this->tokens = std::vector<Token>();
 
-            keywords = std::unordered_map<std::string, Type>();
+            keywords = {};
             keywords["and"] = Type::LOG_AND;
             keywords["class"] = Type::CLASS;
             keywords["false"] = Type::FALSE;
@@ -48,6 +48,7 @@ namespace rift
             keywords["super"] = Type::SUPER;
             keywords["this"] = Type::THIS;
             keywords["true"] = Type::TRUE;
+            keywords["mut!"] = Type::CONST;
             keywords["mut"] = Type::VAR;
             keywords["while"] = Type::WHILE;
         }
diff --git a/lib/scanner/tokens.cc b/lib/scanner/tokens.cc
index 7411f2e..eaef7c0 100644
--- a/lib/scanner/tokens.cc
+++ b/lib/scanner/tokens.cc
@@ -67,7 +67,9 @@ std::string Token::convertTypeString(TokenType type) {
         case THIS: return "THIS";
         case TRUE: return "TRUE";
         case VAR: return "VAR";
+        case CONST: return "CONST";
         case WHILE: return "WHILE";
+        case C_IDENTIFIER: return "C_IDENTIFIER";
         case IGNORE: return "IGNORE";
         case EOFF: return "EOFF";
     }
@@ -209,7 +211,7 @@ std::any Token::getLiteral() const
 
 #pragma mark - Operators
 
-bool Token::operator==(const Token &token)
+bool Token::operator==(const Token &token) const
 {
     return this->type == token.type;
 }
\ No newline at end of file