From 8581abcc0c80de312a0b62f33e8faffe75b64e6b Mon Sep 17 00:00:00 2001
From: Alex Kotov <kotovalexarian@gmail.com>
Date: Fri, 5 May 2023 14:03:32 +0400
Subject: [PATCH] Add booleans

---
 src/builtins.c |   2 +-
 src/ctype.c    |  13 +-
 src/ctype.h    |   1 +
 src/lexer.c    |  63 ++++++++++
 src/main.c     | 320 +++++++++++++++++++------------------------------
 src/object.c   |   2 +-
 src/parser.c   |  16 +++
 src/tokens.c   |   1 +
 src/tokens.h   |   1 +
 9 files changed, 219 insertions(+), 200 deletions(-)

diff --git a/src/builtins.c b/src/builtins.c
index 3583564..87d873c 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -293,7 +293,7 @@ struct Object *func_display(struct Object *const args)
         printf(")");
         break;
     case TYPE_BOOLEAN:
-        printf("%s", object->boolean ? "#t" : "#f");
+        printf("%s", object->boolean ? "#true" : "#false");
         break;
     case TYPE_CHAR:
         printf("#\\TODO"); // TODO
diff --git a/src/ctype.c b/src/ctype.c
index c4bb557..b9012e4 100644
--- a/src/ctype.c
+++ b/src/ctype.c
@@ -2,7 +2,7 @@
 
 #include <ctype.h>
 
-bool is_space(char chr)
+bool is_space(const char chr)
 {
     // ' '  (space)
     // '\f' (form-feed)
@@ -13,7 +13,12 @@ bool is_space(char chr)
     return isspace(chr);
 }
 
-bool is_ident_head(char chr)
+bool is_tag(const char chr)
+{
+    return isalnum(chr);
+}
+
+bool is_ident_head(const char chr)
 {
     return isalpha(chr) ||
       chr == '!' ||
@@ -36,12 +41,12 @@ bool is_ident_head(char chr)
       chr == '~';
 }
 
-bool is_ident_tail(char chr)
+bool is_ident_tail(const char chr)
 {
     return is_ident_head(chr) || isdigit(chr);
 }
 
-bool is_number(char chr)
+bool is_number(const char chr)
 {
     return isdigit(chr);
 }
diff --git a/src/ctype.h b/src/ctype.h
index 2d293ac..5d30daa 100644
--- a/src/ctype.h
+++ b/src/ctype.h
@@ -4,6 +4,7 @@
 #include <stdbool.h>
 
 bool is_space(char chr);
+bool is_tag(char chr);
 bool is_ident_head(char chr);
 bool is_ident_tail(char chr);
 bool is_number(char chr);
diff --git a/src/lexer.c b/src/lexer.c
index b2259f6..b0dc7e4 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -17,6 +17,8 @@ enum State {
     STATE_CURLY_OPEN,
     STATE_CURLY_CLOSE,
     STATE_QUOTE,
+    STATE_SHARP,
+    STATE_TAG,
     STATE_IDENT,
     STATE_NUM,
 };
@@ -58,6 +60,7 @@ State_to_token_type(const enum State state, enum TokenType *const token_type)
     case STATE_CURLY_CLOSE:  *token_type = TOKEN_CURLY_CLOSE;  break;
     case STATE_QUOTE:        *token_type = TOKEN_QUOTE;        break;
     case STATE_IDENT:        *token_type = TOKEN_IDENT;        break;
+    case STATE_TAG:          *token_type = TOKEN_TAG;          break;
     case STATE_NUM:          *token_type = TOKEN_NUM;          break;
     default: return false;
     }
@@ -112,6 +115,8 @@ void Lexer_lex(const Lexer self, const char chr)
         } else if (chr == '\'') {
             state = STATE_QUOTE;
             buffer_add(chr);
+        } else if (chr == '#') {
+            state = STATE_SHARP;
         } else if (is_space(chr)) {
             state = STATE_WHITESPACE;
             buffer_add(chr);
@@ -161,6 +166,10 @@ void Lexer_lex(const Lexer self, const char chr)
             buffer_clean();
             state = STATE_QUOTE;
             buffer_add(chr);
+        } else if (chr == '#') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_SHARP;
         } else if (is_space(chr)) {
             buffer_add(chr);
         } else if (is_ident_head(chr)) {
@@ -219,6 +228,10 @@ void Lexer_lex(const Lexer self, const char chr)
             buffer_clean();
             state = STATE_QUOTE;
             buffer_add(chr);
+        } else if (chr == '#') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_SHARP;
         } else if (is_space(chr)) {
             token_add(self->tokens, state, buffer);
             buffer_clean();
@@ -238,6 +251,56 @@ void Lexer_lex(const Lexer self, const char chr)
             abort();
         }
         break;
+    case STATE_SHARP:
+        if (is_tag(chr)) {
+            state = STATE_TAG;
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
+    case STATE_TAG:
+        if (chr == '(') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_ROUND_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_ROUND_CLOSE;
+            buffer_add(chr);
+        } else if (chr == '[') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_SQUARE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ']') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_SQUARE_CLOSE;
+            buffer_add(chr);
+        } else if (chr == '{') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_CURLY_OPEN;
+            buffer_add(chr);
+        } else if (chr == '}') {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_CURLY_CLOSE;
+            buffer_add(chr);
+        } else if (is_space(chr)) {
+            token_add(self->tokens, state, buffer);
+            buffer_clean();
+            state = STATE_WHITESPACE;
+            buffer_add(chr);
+        } else if (is_tag(chr)) {
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
     case STATE_IDENT:
         if (chr == '(') {
             token_add(self->tokens, state, buffer);
diff --git a/src/main.c b/src/main.c
index 4951f09..22333a2 100644
--- a/src/main.c
+++ b/src/main.c
@@ -260,8 +260,8 @@ void test()
     struct Object *const sharp_true = Object_new_boolean(true);
     struct Object *const num_123    = Object_new_number(123);
 
-    // #t
-    // #t
+    // #true
+    // #true
     assert(eval(sharp_true) == sharp_true);
 
     // 123
@@ -276,8 +276,8 @@ void test()
         ) == sym_foo
     );
 
-    // (quote #t)
-    // #t
+    // (quote #true)
+    // #true
     assert(
         eval(
             Object_build_list(2, Object_new_symbol("quote"), sharp_true)
@@ -306,7 +306,7 @@ void test_if()
     struct Object *const num_123 = Object_new_number(123);
     struct Object *const num_456 = Object_new_number(456);
 
-    // (if #t 123 456)
+    // (if #true 123 456)
     assert(eval(Object_build_list(
         4,
         Object_new_symbol("if"),
@@ -324,7 +324,7 @@ void test_if()
         num_456
     )) == num_123);
 
-    // (if #f 123 456)
+    // (if #false 123 456)
     assert(eval(Object_build_list(
         4,
         Object_new_symbol("if"),
@@ -419,31 +419,23 @@ void test_list()
 void test_booleanQN()
 {
     // (boolean? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(boolean? +)")));
 
     // (boolean? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(boolean? '())")));
 
-    // (boolean? #t)
-    // #t
-    assert(Object_is_true(eval(Object_build_list(
-        2,
-        Object_new_symbol("boolean?"),
-        Object_new_boolean(true)
-    ))));
+    // (boolean? #true)
+    // #true
+    assert(Object_is_true(eval_str("(boolean? #true)")));
 
-    // (boolean? #f)
-    // #t
-    assert(Object_is_true(eval(Object_build_list(
-        2,
-        Object_new_symbol("boolean?"),
-        Object_new_boolean(false)
-    ))));
+    // (boolean? #false)
+    // #true
+    assert(Object_is_true(eval_str("(boolean? #false)")));
 
     // (boolean? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("boolean?"),
@@ -451,11 +443,11 @@ void test_booleanQN()
     ))));
 
     // (boolean? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(boolean? 'foo)")));
 
     // (boolean? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("boolean?"),
@@ -463,42 +455,34 @@ void test_booleanQN()
     ))));
 
     // (boolean? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(boolean? 123)")));
 
     // (boolean? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(boolean? (cons 123 456))")));
 }
 
 void test_charQN()
 {
     // (char? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(char? +)")));
 
     // (char? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(char? '())")));
 
-    // (char? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("char?"),
-        Object_new_boolean(true)
-    ))));
+    // (char? #true)
+    // #false
+    assert(Object_is_false(eval_str("(char? #true)")));
 
-    // (char? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("char?"),
-        Object_new_boolean(false)
-    ))));
+    // (char? #false)
+    // #false
+    assert(Object_is_false(eval_str("(char? #false)")));
 
     // (char? #\n)
-    // #t
+    // #true
     assert(Object_is_true(eval(Object_build_list(
         2,
         Object_new_symbol("char?"),
@@ -506,11 +490,11 @@ void test_charQN()
     ))));
 
     // (char? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(char? 'foo)")));
 
     // (char? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("char?"),
@@ -518,42 +502,34 @@ void test_charQN()
     ))));
 
     // (char? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(char? 123)")));
 
     // (char? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(char? (cons 123 456))")));
 }
 
 void test_nullQN()
 {
     // (null? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(null? +)")));
 
     // (null? '())
-    // #t
+    // #true
     assert(Object_is_true(eval_str("(null? '())")));
 
-    // (null? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("null?"),
-        Object_new_boolean(true)
-    ))));
+    // (null? #true)
+    // #false
+    assert(Object_is_false(eval_str("(null? #true)")));
 
-    // (null? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("null?"),
-        Object_new_boolean(false)
-    ))));
+    // (null? #false)
+    // #false
+    assert(Object_is_false(eval_str("(null? #false)")));
 
     // (null? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("null?"),
@@ -561,11 +537,11 @@ void test_nullQN()
     ))));
 
     // (null? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(null? 'foo)")));
 
     // (null? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("null?"),
@@ -573,42 +549,34 @@ void test_nullQN()
     ))));
 
     // (null? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(null? 123)")));
 
     // (null? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(null? (cons 123 456))")));
 }
 
 void test_numberQN()
 {
     // (number? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(number? +)")));
 
     // (number? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(number? '())")));
 
-    // (number? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("number?"),
-        Object_new_boolean(true)
-    ))));
+    // (number? #true)
+    // #false
+    assert(Object_is_false(eval_str("(number? #true)")));
 
-    // (number? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("number?"),
-        Object_new_boolean(false)
-    ))));
+    // (number? #false)
+    // #false
+    assert(Object_is_false(eval_str("(number? #false)")));
 
     // (number? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("number?"),
@@ -616,11 +584,11 @@ void test_numberQN()
     ))));
 
     // (number? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(number? 'foo)")));
 
     // (number? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("number?"),
@@ -628,42 +596,34 @@ void test_numberQN()
     ))));
 
     // (number? 123)
-    // #t
+    // #true
     assert(Object_is_true(eval_str("(number? 123)")));
 
     // (number? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(number? (cons 123 456))")));
 }
 
 void test_pairQN()
 {
     // (pair? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(pair? +)")));
 
     // (pair? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(pair? '())")));
 
-    // (pair? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("pair?"),
-        Object_new_boolean(true)
-    ))));
+    // (pair? #true)
+    // #false
+    assert(Object_is_false(eval_str("(pair? #true)")));
 
-    // (pair? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("pair?"),
-        Object_new_boolean(false)
-    ))));
+    // (pair? #false)
+    // #false
+    assert(Object_is_false(eval_str("(pair? #false)")));
 
     // (pair? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("pair?"),
@@ -671,11 +631,11 @@ void test_pairQN()
     ))));
 
     // (pair? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(pair? 'foo)")));
 
     // (pair? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("pair?"),
@@ -683,42 +643,34 @@ void test_pairQN()
     ))));
 
     // (pair? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(pair? 123)")));
 
     // (pair? (cons 123 456))
-    // #t
+    // #true
     assert(Object_is_true(eval_str("(pair? (cons 123 456))")));
 }
 
 void test_procedureQN()
 {
     // (procedure? +)
-    // #t
+    // #true
     assert(Object_is_true(eval_str("(procedure? +)")));
 
     // (procedure? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(procedure? '())")));
 
-    // (procedure? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("procedure?"),
-        Object_new_boolean(true)
-    ))));
+    // (procedure? #true)
+    // #false
+    assert(Object_is_false(eval_str("(procedure? #true)")));
 
-    // (procedure? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("procedure?"),
-        Object_new_boolean(false)
-    ))));
+    // (procedure? #false)
+    // #false
+    assert(Object_is_false(eval_str("(procedure? #false)")));
 
     // (procedure? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("procedure?"),
@@ -726,11 +678,11 @@ void test_procedureQN()
     ))));
 
     // (procedure? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(procedure? 'foo)")));
 
     // (procedure? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("procedure?"),
@@ -738,42 +690,34 @@ void test_procedureQN()
     ))));
 
     // (procedure? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(procedure? 123)")));
 
     // (procedure? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(procedure? (cons 123 456))")));
 }
 
 void test_stringQN()
 {
     // (string? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(string? +)")));
 
     // (string? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(string? '())")));
 
-    // (string? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("string?"),
-        Object_new_boolean(true)
-    ))));
+    // (string? #true)
+    // #false
+    assert(Object_is_false(eval_str("(string? #true)")));
 
-    // (string? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("string?"),
-        Object_new_boolean(false)
-    ))));
+    // (string? #false)
+    // #false
+    assert(Object_is_false(eval_str("(string? #false)")));
 
     // (string? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("string?"),
@@ -781,11 +725,11 @@ void test_stringQN()
     ))));
 
     // (string? 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(string? 'foo)")));
 
     // (string? "foo")
-    // #t
+    // #true
     assert(Object_is_true(eval(Object_build_list(
         2,
         Object_new_symbol("string?"),
@@ -793,42 +737,34 @@ void test_stringQN()
     ))));
 
     // (string? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(string? 123)")));
 
     // (string? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(string? (cons 123 456))")));
 }
 
 void test_symbolQN()
 {
     // (symbol? +)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(symbol? +)")));
 
     // (symbol? '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(symbol? '())")));
 
-    // (symbol? #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("symbol?"),
-        Object_new_boolean(true)
-    ))));
+    // (symbol? #true)
+    // #false
+    assert(Object_is_false(eval_str("(symbol? #true)")));
 
-    // (symbol? #f)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("symbol?"),
-        Object_new_boolean(false)
-    ))));
+    // (symbol? #false)
+    // #false
+    assert(Object_is_false(eval_str("(symbol? #false)")));
 
     // (symbol? #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("symbol?"),
@@ -836,11 +772,11 @@ void test_symbolQN()
     ))));
 
     // (symbol? 'foo)
-    // #t
+    // #true
     assert(Object_is_true(eval_str("(symbol? 'foo)")));
 
     // (symbol? "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("symbol?"),
@@ -848,11 +784,11 @@ void test_symbolQN()
     ))));
 
     // (symbol? 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(symbol? 123)")));
 
     // (symbol? (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(symbol? (cons 123 456))")));
 }
 
@@ -887,30 +823,26 @@ void test_numberTOstring()
     assert(strcmp(result->s, "1e240") == 0);
 }
 
+/*********************
+ * Logical operators *
+ *********************/
+
 void test_not()
 {
     // (not '())
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(not '())")));
 
-    // (not #t)
-    // #f
-    assert(Object_is_false(eval(Object_build_list(
-        2,
-        Object_new_symbol("not"),
-        Object_new_boolean(true)
-    ))));
+    // (not #true)
+    // #false
+    assert(Object_is_false(eval_str("(not #true)")));
 
-    // (not #f)
-    // #t
-    assert(Object_is_true(eval(Object_build_list(
-        2,
-        Object_new_symbol("not"),
-        Object_new_boolean(false)
-    ))));
+    // (not #false)
+    // #true
+    assert(Object_is_true(eval_str("(not #false)")));
 
     // (not #\n)
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("not"),
@@ -918,11 +850,11 @@ void test_not()
     ))));
 
     // (not 'foo)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(not 'foo)")));
 
     // (not "foo")
-    // #f
+    // #false
     assert(Object_is_false(eval(Object_build_list(
         2,
         Object_new_symbol("not"),
@@ -930,10 +862,10 @@ void test_not()
     ))));
 
     // (not 123)
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(not 123)")));
 
     // (not (cons 123 456))
-    // #f
+    // #false
     assert(Object_is_false(eval_str("(not (cons 123 456))")));
 }
diff --git a/src/object.c b/src/object.c
index 16bcc20..ecd5530 100644
--- a/src/object.c
+++ b/src/object.c
@@ -190,7 +190,7 @@ void Object_print(struct Object *const self, const unsigned indent)
         Object_print(self->pair.b, indent + 1);
         break;
     case TYPE_BOOLEAN:
-        printf("%s\n", self->boolean ? "#t" : "#f");
+        printf("%s\n", self->boolean ? "#true" : "#false");
         break;
     case TYPE_CHAR:
         printf("%c\n", self->chr);
diff --git a/src/parser.c b/src/parser.c
index f677b48..4daaa36 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -6,6 +6,7 @@
 #include <assert.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 
 static void expect(Tokens tokens, enum TokenType token_type);
 
@@ -35,6 +36,21 @@ struct Object *expr(const Tokens tokens)
     case TOKEN_QUOTE:
         Tokens_pop(tokens);
         return Object_build_list(2, Object_new_symbol("quote"), expr(tokens));
+    case TOKEN_TAG:
+    {
+        struct Object *object = NULL;
+        const char *const val = Tokens_top(tokens)->val;
+        assert(val);
+        if (strcmp(val, "f") == 0 || strcmp(val, "false") == 0) {
+            object = Object_new_boolean(false);
+        } else if (strcmp(val, "t") == 0 || strcmp(val, "true") == 0) {
+            object = Object_new_boolean(true);
+        } else {
+            assert(0);
+        }
+        Tokens_pop(tokens);
+        return object;
+    }
     case TOKEN_IDENT:
     {
         struct Object *const object = Object_new_symbol(Tokens_top(tokens)->val);
diff --git a/src/tokens.c b/src/tokens.c
index 196c8bc..0ea2dc9 100644
--- a/src/tokens.c
+++ b/src/tokens.c
@@ -16,6 +16,7 @@ const char *TokenType_to_str(const enum TokenType token_type)
     case TOKEN_CURLY_OPEN:   return "TOKEN_CURLY_OPEN";
     case TOKEN_CURLY_CLOSE:  return "TOKEN_CURLY_CLOSE";
     case TOKEN_QUOTE:        return "TOKEN_QUOTE";
+    case TOKEN_TAG:          return "TOKEN_TAG";
     case TOKEN_IDENT:        return "TOKEN_IDENT";
     case TOKEN_NUM:          return "TOKEN_NUM";
     }
diff --git a/src/tokens.h b/src/tokens.h
index 3ed8255..01d66e3 100644
--- a/src/tokens.h
+++ b/src/tokens.h
@@ -17,6 +17,7 @@ enum TokenType {
     TOKEN_CURLY_OPEN,
     TOKEN_CURLY_CLOSE,
     TOKEN_QUOTE,
+    TOKEN_TAG,
     TOKEN_IDENT,
     TOKEN_NUM,
 };