diff --git a/README.md b/README.md
index 8758f41..095849c 100644
--- a/README.md
+++ b/README.md
@@ -8,13 +8,13 @@ A very cool language
 * Sometimes works
 
 ## Syntax
-```go
+```swift
 func fib[n: I64] : I64
     if n <= 1
         return n
     return fib(n-2) + fib(n-1)
 
 func main[] : I64
-    for i in 0..20
+    for i in 0:20
         fib(i) |> I64.to_string() |> print()
 ```
\ No newline at end of file
diff --git a/examples/euler4.zr b/examples/euler4.zr
index 2a32079..a77a1c1 100644
--- a/examples/euler4.zr
+++ b/examples/euler4.zr
@@ -5,7 +5,7 @@ func main[] : I64
         for b in 500:1000
             if a * b > out
                 let s: String = I64.to_string(a * b)
-                let s_rev: String = strrev(s)
+                let s_rev: String = String.rev(s)
                 if strcmp(s, s_rev) == 0
                     out = a * b
                 free(s)
diff --git a/src/codegen_x86_64.rs b/src/codegen_x86_64.rs
index b90ad4e..d4fd18b 100644
--- a/src/codegen_x86_64.rs
+++ b/src/codegen_x86_64.rs
@@ -115,9 +115,11 @@ extern ftell
 extern fread
 extern rewind
 extern system
+extern opendir
+extern readdir
+extern closedir
 extern exit
 extern gettimeofday
-copystr equ strdup
 
 String.nth:
     movzx rax, byte [rdi + rsi]
@@ -127,7 +129,7 @@ String.set:
     mov [rdi + rsi], dl
     ret
 
-time:
+OS.time:
     push rbx
     sub rsp, 16
     mov rbx, rsp
@@ -144,6 +146,47 @@ time:
     pop rbx
     ret
 
+OS.listdir:
+    push r14
+    push rbx
+    push rax
+    mov r14, rdi
+    call Array.new
+    mov rbx, rax
+    mov rdi, r14
+    call opendir
+    mov r14, rax
+.LBB5_1:
+    mov rdi, r14
+    call readdir
+    test rax, rax
+    je .LBB5_7
+    cmp byte [rax+19], 46
+    jne .LBB5_6
+    movzx ecx, byte [rax+20]
+    test ecx, ecx
+    je .LBB5_1
+    cmp ecx, 46
+    jne .LBB5_6
+    cmp byte [rax+21], 0
+    je .LBB5_1
+.LBB5_6:
+    add rax, 19
+    mov rdi, rax
+    call strdup
+    mov rsi, rax
+    mov rdi, rbx
+    call Array.push
+    jmp .LBB5_1
+.LBB5_7:
+    mov rdi, r14
+    call closedir
+    mov rax, rbx
+    add rsp, 8
+    pop rbx
+    pop r14
+    ret
+
 Array.new:
     mov rdi, 1
     mov rsi, 24
diff --git a/src/std.zr b/src/std.zr
index 10ee35d..6b8556c 100644
--- a/src/std.zr
+++ b/src/std.zr
@@ -19,7 +19,7 @@ func substr[s: String, start: I64, length: I64] : String
     strlcpy(out, s + start, length + 1)
     return out
 
-func strrev[s: String] : String
+func String.rev[s: String] : String
     let len: I64 = strlen(s)
     let out: String = malloc(len + 1)
 
diff --git a/test.zr b/test.zr
index c4bc77a..ddd6776 100644
--- a/test.zr
+++ b/test.zr
@@ -3,39 +3,26 @@ func run_test[x: String] : I64
     printf("\033[93mBuilding %s...\033[0m", x)
     let cmd: String = concat("./target/release/zern examples/", x)
 
-    let build_start_time: I64 = time()
+    let build_start_time: I64 = OS.time()
     if system(cmd) != 0
         exit(1)
-    let build_end_time: I64 = time()
+    let build_end_time: I64 = OS.time()
 
     free(cmd)
     printf(" %ldms\n", build_end_time - build_start_time)
 
-    let run_start_time: I64 = time()
+    let run_start_time: I64 = OS.time()
     if system("./out") != 0
         exit(1)
-    let run_end_time: I64 = time()
+    let run_end_time: I64 = OS.time()
     
     printf("\033[93mRunning %s...\033[0m %ldms\n", x, run_end_time - run_start_time)
 
 func main[] : I64
     system("cargo build --release")
 
-    // TODO: listdir
-    run_test("euler1.zr")
-    run_test("euler2.zr")
-    run_test("euler3.zr")
-    run_test("euler4.zr")
-    run_test("euler5.zr")
-    run_test("euler6.zr")
-    run_test("euler7.zr")
-    run_test("euler8.zr")
-    run_test("euler9.zr")
-    run_test("euler10.zr")
-    run_test("euler12.zr")
-    run_test("euler13.zr")
-    run_test("euler14.zr")
-    run_test("euler15.zr")
-    run_test("fib.zr")
-    run_test("hello.zr")
-    run_test("strings.zr")
\ No newline at end of file
+    let files: Array = OS.listdir("examples/")
+    for i in 0:Array.size(files)
+        let file: String = Array.nth(files, i)
+        run_test(file)
+        free(file)
\ No newline at end of file