diff --git a/README.md b/README.md
index 2f9101e..194e57c 100644
--- a/README.md
+++ b/README.md
@@ -4,12 +4,12 @@ A very cool language
 
 ## Syntax
 ```go
-func fib[n: U32] : U32
+func fib[n: I64] : I64
     if n <= 1
         return n
     return fib(n-2) + fib(n-1)
 
-func main[]
+func main[] : I64
     for i in 0..20
-        fib(i) |> U32.to_string() |> IO.print()
+        fib(i) |> I64.to_string() |> print()
 ```
\ No newline at end of file
diff --git a/examples/euler10.zr b/examples/euler10.zr
index 57b3e80..db23dff 100644
--- a/examples/euler10.zr
+++ b/examples/euler10.zr
@@ -3,18 +3,18 @@ func print_i64[x: I64] : I64
 
 func is_prime[n: I64]: I64
     if n <= 1
-        return 0
+        return false
     if n == 2 || n == 3
-        return 1
+        return true
     if n % 2 == 0 || n % 3 == 0
-        return 0
-    
+        return false
+
     let i: I64 = 5
     while i * i <= n
         if n % i == 0 || n % (i + 2) == 0
-            return 0
+            return false
         i = i + 6
-    return 1
+    return true
 
 func main[] : I64
     let sum: I64 = 0
diff --git a/examples/euler12.zr b/examples/euler12.zr
index c358b2e..c18b91e 100644
--- a/examples/euler12.zr
+++ b/examples/euler12.zr
@@ -3,7 +3,7 @@ func print_i64[x: I64] : I64
 
 func num_divisors[n: I64] : I64
     let end: I64 = isqrt(n)
-    
+
     let result: I64 = 0
     let i: I64 = 1
     while i < end + 1
diff --git a/examples/euler4.zr b/examples/euler4.zr
index 454283a..66b9c2a 100644
--- a/examples/euler4.zr
+++ b/examples/euler4.zr
@@ -1,7 +1,7 @@
 func print_i64[x: I64] : I64
     printf("%ld\n", x)
 
-func i64_to_string[n: I64] : String
+func I64.to_string[n: I64] : String
     let x: I64 = malloc(21)
     sprintf(x, "%ld", n)
     return x
@@ -14,7 +14,7 @@ func main[] : I64
         let b: I64 = 500
         while b < 1000
             if a * b > out
-                let s: String = i64_to_string(a * b)
+                let s: String = I64.to_string(a * b)
                 let s_rev: String = strrev(s)
                 if strcmp(s, s_rev) == 0
                     out = a * b
diff --git a/examples/euler7.zr b/examples/euler7.zr
index 9b4c0a8..b4b08a0 100644
--- a/examples/euler7.zr
+++ b/examples/euler7.zr
@@ -3,18 +3,18 @@ func print_i64[x: I64] : I64
 
 func is_prime[n: I64]: I64
     if n <= 1
-        return 0
+        return false
     if n == 2 || n == 3
-        return 1
+        return true
     if n % 2 == 0 || n % 3 == 0
-        return 0
-    
+        return false
+
     let i: I64 = 5
     while i * i <= n
         if n % i == 0 || n % (i + 2) == 0
-            return 0
+            return false
         i = i + 6
-    return 1
+    return true
 
 func main[] : I64
     let found: I64 = 0
diff --git a/examples/strings.zr b/examples/strings.zr
index 5b0318b..f6ba059 100644
--- a/examples/strings.zr
+++ b/examples/strings.zr
@@ -1,12 +1,12 @@
 func print_i64[x: I64] : I64
     printf("%ld\n", x)
 
-func i64_to_string[n: I64] : String
-    let x: I64 = malloc(21)
-    sprintf(x, "%d", n)
+func I64.to_string[n: I64] : String
+    let x: String = malloc(21)
+    sprintf(x, "%ld", n)
     return x
 
 func main[] : I64
-    let s: String = i64_to_string(58394)
+    let s: String = I64.to_string(58394)
     print_i64(strlen(s))
     free(s)
\ No newline at end of file
diff --git a/src/codegen_x86_64.rs b/src/codegen_x86_64.rs
index f7c55a2..e5cf401 100644
--- a/src/codegen_x86_64.rs
+++ b/src/codegen_x86_64.rs
@@ -58,7 +58,7 @@ macro_rules! emit {
 }
 
 static REGISTERS: [&str; 6] = ["rdi", "rsi", "rdx", "rcx", "r8", "r9"];
-static TYPES: [&str; 2] = ["I64", "String"];
+static TYPES: [&str; 3] = ["I64", "String", "Bool"];
 
 pub struct CodegenX86_64 {
     output: String,
@@ -259,7 +259,11 @@ nth:
 
                 self.compile_stmt(env, *body)?;
 
-                emit!(&mut self.output, "    mov rax, 0"); // TODO: remove default return value
+                if name.lexeme == "main" {
+                    // default exit code
+                    emit!(&mut self.output, "    mov rax, 0");
+                }
+
                 emit!(&mut self.output, "    mov rsp, rbp");
                 emit!(&mut self.output, "    pop rbp");
                 emit!(&mut self.output, "    ret");
@@ -366,6 +370,12 @@ nth:
                     emit!(&mut self.output, "    mov rax, S{}", self.data_counter);
                     self.data_counter += 1;
                 }
+                TokenType::True => {
+                    emit!(&mut self.output, "    mov rax, 1");
+                }
+                TokenType::False => {
+                    emit!(&mut self.output, "    mov rax, 0");
+                }
                 _ => unreachable!(),
             },
             Expr::Unary { op, right } => {
diff --git a/src/parser.rs b/src/parser.rs
index 7f0ba5f..9dfcdcd 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -396,7 +396,12 @@ impl Parser {
     }
 
     fn primary(&mut self) -> Result<Expr, ZernError> {
-        if self.match_token(&[TokenType::Number, TokenType::String]) {
+        if self.match_token(&[
+            TokenType::Number,
+            TokenType::String,
+            TokenType::True,
+            TokenType::False,
+        ]) {
             Ok(Expr::Literal(self.previous().clone()))
         } else if self.match_token(&[TokenType::LeftParen]) {
             let expr = self.expression()?;
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index 4ff4222..e911fca 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -30,6 +30,8 @@ pub enum TokenType {
     Identifier,
     String,
     Number,
+    True,
+    False,
 
     KeywordLet,
     KeywordIf,
@@ -305,6 +307,8 @@ impl Tokenizer {
             "while" => TokenType::KeywordWhile,
             "func" => TokenType::KeywordFunc,
             "return" => TokenType::KeywordReturn,
+            "true" => TokenType::True,
+            "false" => TokenType::False,
             _ => TokenType::Identifier,
         })
     }