diff --git a/lib/src/io.gsc b/lib/src/io.gsc
index 1adb655..d57b1f9 100644
--- a/lib/src/io.gsc
+++ b/lib/src/io.gsc
@@ -22,33 +22,33 @@ handle: nullHandle = 0 as handle
 # -- Implementation note
 # On Linux this will return 0 as is it convention under UNIX (see: https://www.man7.org/linux/man-pages/man3/stdin.3.html)
 # On Windows the library will call `GetStdHandle(STD_INPUT_HANDLE)`
-fun getStdinHandle(out handle: stdin)
+fun handle:getStdinHandle()
 
 # Returns a handle to this processes standard input I/O handle
 # -- Implementation note
 # On Linux this will return 1 as is it convention under UNIX (see: https://www.man7.org/linux/man-pages/man3/stdout.3.html)
 # On Windows the library will call `GetStdHandle(STD_OUTPUT_HANDLE)`
-fun getStdoutHandle(out handle: stdout)
+fun handle:getStdoutHandle()
 
 # Returns a handle to this processes standard input I/O handle
 # -- Implementation note
 # On Linux this will return 1 as is it convention under UNIX (see: https://www.man7.org/linux/man-pages/man3/stderr.3.html)
 # On Windows the library will call `GetStdHandle(STD_OUTPUT_HANDLE)`
-fun getStderrHandle(out handle: stderr)
+fun handle:getStderrHandle()
 
 # Write `len` number of bytes from `buf` into the I/O resource specified
 # by `dev`. Returns the number of bytes written.
 # -- Implementation note
 # On Linux this will use the syscall write
 # On Windows this will use the WriteFile function
-fun writeBytes(in handle: dev, in ref u8: buf, in u32: len)(out u32: written)
+fun u32:writeBytes(in handle: dev, in ref u8: buf, in u32: len)
 
 # Read atmost `len` bytes to `buf` from the I/O resource specified by `dev`
 # Returns the number of read bytes in `written`
 # -- Implementation note
 # On Linux this will use the syscall read
 # On Windows this will use the ReadFile function
-fun readBytes(in handle: dev, in ref u8: buf, in u32: len)(out u32: read)
+fun u32:readBytes(in handle: dev, in ref u8: buf, in u32: len)
 
 # Flushes the buffers of the I/O resource specified by `dev`
 # -- Implementation note
diff --git a/lib/src/io/api.h b/lib/src/io/api.h
index c642185..0064b9a 100644
--- a/lib/src/io/api.h
+++ b/lib/src/io/api.h
@@ -6,15 +6,15 @@
 
 typedef ptr handle;
 
-void getStdinHandle(handle* stdin);
+handle getStdinHandle();
 
-void getStdoutHandle(handle* stdout);
+handle getStdoutHandle();
 
-void getStderrHandle(handle* stderr);
+handle getStderrHandle();
 
-void writeBytes(handle dev, u8* buf, u32 len, u32* written);
+u32 writeBytes(handle dev, u8* buf, u32 len);
 
-void readBytes(handle dev, u8* buf, u32 len, u32* read);
+u32 readBytes(handle dev, u8* buf, u32 len);
 
 void flush(handle dev);
 
diff --git a/lib/src/io/impl.c b/lib/src/io/impl.c
index 4de453b..5879375 100644
--- a/lib/src/io/impl.c
+++ b/lib/src/io/impl.c
@@ -11,24 +11,28 @@
 // FIXME: error in case GetStdHandle return INVALID_HANDLE_VALUE 
 // FIXME: error in case functions return 0 
 
-void getStdinHandle(handle* stdin) {
-    *stdin = (handle) GetStdHandle(STD_INPUT_HANDLE);
+handle getStdinHandle(handle* stdin) {
+    return GetStdHandle(STD_INPUT_HANDLE);
 }
 
-void getStdoutHandle(handle* stdout) {
-    *stdout = (handle) GetStdHandle(STD_OUTPUT_HANDLE);
+handle getStdoutHandle(handle* stdout) {
+    return GetStdHandle(STD_OUTPUT_HANDLE);
 }
 
-void getStderrHandle(handle* stderr) {
-    *stderr = (handle) GetStdHandle(STD_ERROR_HANDLE);
+handle getStderrHandle(handle* stderr) {
+    return GetStdHandle(STD_ERROR_HANDLE);
 }
 
-void writeBytes(handle dev, u8* buf, u32 len, u32* bytesWritten) {
-    WriteFile((HANDLE) dev, buf, len, bytesRead, NULL);
+u32 writeBytes(handle dev, u8* buf, u32 len) {
+    u32 bytesWritten = 0;
+    WriteFile((HANDLE) dev, buf, len, &bytesWritten, NULL);
+    return bytesWritten;
 }
 
-void readBytes(handle dev, u8* buf, u32 len, u32* bytesRead) {
-    ReadFile((HANDLE) dev, buf, len, bytesRead, NULL);
+u32 readBytes(handle dev, u8* buf, u32 len) {
+    u32 bytesRead = 0;
+    ReadFile((HANDLE) dev, buf, len, &bytesRead, NULL);
+    return bytesRead;
 }
 
 void flush(handle dev) {
@@ -47,24 +51,24 @@ void flush(handle dev) {
 // which are stored as 64-bit by zero extending
 #define TO_INT(x) ((int)(long int)(x))
 
-void getStdinHandle(handle* stdin) {
-    *stdin = (handle) STDIN_FILENO;
+handle getStdinHandle() {
+    return (handle) STDIN_FILENO;
 }
 
-void getStdoutHandle(handle* stdout) {
-    *stdout = (handle) STDOUT_FILENO;
+handle getStdoutHandle() {
+    return (handle) STDOUT_FILENO;
 }
 
-void getStderrHandle(handle* stderr) {
-    *stderr = (handle) STDERR_FILENO;
+handle getStderrHandle() {
+    return (handle) STDERR_FILENO;
 }
 
-void writeBytes(handle dev, u8* buf, u32 len, u32* bytesWritten) {
-    *bytesWritten = write(TO_INT(dev), buf, len);
+u32 writeBytes(handle dev, u8* buf, u32 len) {
+    return write(TO_INT(dev), buf, len);
 }
 
-void readBytes(handle dev, u8* buf, u32 len, u32* bytesRead) {
-    *bytesRead = read(TO_INT(dev), buf, len);
+u32 readBytes(handle dev, u8* buf, u32 len) {
+    return read(TO_INT(dev), buf, len);
 }
 
 void flush(handle dev) {
diff --git a/tests/stdlib/src/matrix.gsc b/tests/stdlib/src/matrix.gsc
index 21de436..0569dd9 100644
--- a/tests/stdlib/src/matrix.gsc
+++ b/tests/stdlib/src/matrix.gsc
@@ -50,15 +50,13 @@ fun printU32(in u32: val)
 
     u32ToCstr(val)(str, len)
 
-    handle: stdout = nullHandle
-    getStdoutHandle(stdout)
+    handle: stdout = getStdoutHandle()
 
-    u32: written = 0 as u32
-    writeBytes(stdout, str, len, written)
+    writeBytes(stdout, str, len)
 
     heapFree(str)
 
-    writeBytes(stdout, " ", 1 as u32, written)
+    writeBytes(stdout, " ", 1 as u32)
 }
 
 fun test_matrix()
@@ -67,8 +65,7 @@ fun test_matrix()
     heapAlloc((8 * 4) as u32)(matrix as ref u8)
 
     u32: written = 0 as u32
-    handle: stdout = nullHandle
-    getStdoutHandle(stdout)
+    handle: stdout = getStdoutHandle()
 
     u32: idx = 0 as u32
     while idx < 4 {
@@ -82,7 +79,7 @@ fun test_matrix()
 
             idy = idy + 1 as u32
         }
-        writeBytes(stdout, "\n", 1 as u32, written)
+        writeBytes(stdout, "\n", 1 as u32)
 
         heapFree(matrix[idx] as ref u8)
         idx = idx + 1 as u32