diff --git a/nixide/src/expr/tests.rs b/nixide/src/expr/tests.rs
index 9d2df97..0b32729 100644
--- a/nixide/src/expr/tests.rs
+++ b/nixide/src/expr/tests.rs
@@ -126,7 +126,7 @@ fn test_value_formatting() {
     assert_eq!(format!("{quoted_str}"), "say \"hello\"");
     assert_eq!(
         format!("{quoted_str:?}"),
-        "Value::String(NixString(say \"hello\"))"
+        "Value::String(NixString(\"say \"hello\"\"))"
     );
 
     // Test null formatting
@@ -141,11 +141,14 @@ fn test_value_formatting() {
         .eval_from_string("{ a = 1; }", "<eval>")
         .expect("Failed to evaluate attrs");
     assert_eq!(format!("{attrs_val}"), "{ <attrs> }");
-    assert_eq!(format!("{attrs_val:?}"), "Value::Attrs({ <attrs> })");
+    assert_eq!(
+        format!("{attrs_val:?}"),
+        "Value::Attrs(NixAttrs({ <attrs> }))"
+    );
 
     let list_val = state
         .eval_from_string("[ 1 2 3 ]", "<eval>")
         .expect("Failed to evaluate list");
     assert_eq!(format!("{list_val}"), "[ <list> ]");
-    assert_eq!(format!("{list_val:?}"), "Value::List([ <list> ])");
+    assert_eq!(format!("{list_val:?}"), "Value::List(NixList([ <list> ]))");
 }
diff --git a/nixide/src/stdext/cchar_ptr.rs b/nixide/src/stdext/cchar_ptr.rs
index 0a91b86..bf1840e 100644
--- a/nixide/src/stdext/cchar_ptr.rs
+++ b/nixide/src/stdext/cchar_ptr.rs
@@ -1,9 +1,9 @@
-use std::ffi::{c_char, CStr};
+use std::ffi::{CStr, c_char};
 use std::slice::from_raw_parts;
 use std::str::from_utf8;
 
-use crate::errors::new_nixide_error;
 use crate::NixideResult;
+use crate::errors::new_nixide_error;
 
 pub trait AsCPtr<T> {
     #[allow(unused)]
@@ -56,7 +56,7 @@ impl CCharPtrExt for *const c_char {
         if self.is_null() || n == 0 {
             return Err(new_nixide_error!(NullPtr));
         }
-        let bytes = unsafe { from_raw_parts(self.cast::<u8>(), n as usize) };
+        let bytes = unsafe { from_raw_parts(self as *const u8, n as usize) };
         match from_utf8(bytes) {
             Ok(s) => Ok(s.to_string()),
             Err(_) => Err(new_nixide_error!(StringNotUtf8)),
diff --git a/nixide/src/util/wrap.rs b/nixide/src/util/wrap.rs
index 33790c9..5b9898e 100644
--- a/nixide/src/util/wrap.rs
+++ b/nixide/src/util/wrap.rs
@@ -38,7 +38,7 @@ macro_rules! nonnull {
             ::std::option::Option::Some(p) => ::std::result::Result::Ok(p),
             ::std::option::Option::None => {
                 ::std::result::Result::Err($crate::errors::new_nixide_error!(NullPtr))
-            }
+            },
         }
     }};
 }
@@ -57,9 +57,7 @@ macro_rules! nix_fn {
 pub(crate) use nix_fn;
 
 macro_rules! nix_ptr_fn {
-    ($callback:expr $(,)? ) => {{
-        $crate::util::wrap::nix_fn!($callback).and_then(|ptr| $crate::util::wrap::nonnull!(ptr))
-    }};
+    ($callback:expr $(,)? ) => {{ $crate::util::wrap::nix_fn!($callback).and_then(|ptr| $crate::util::wrap::nonnull!(ptr)) }};
 }
 pub(crate) use nix_ptr_fn;
 
@@ -114,34 +112,25 @@ pub(crate) use nix_callback;
 
 macro_rules! nix_string_callback {
     ($function:expr $(,)?) => {{
-        #[repr(C)]
-        struct __ReturnType {
-            start: *const ::std::ffi::c_char,
-            n: ::std::ffi::c_uint,
-        }
-
         let __result = $crate::util::wrap::nix_callback!(
-            |start: *const ::std::ffi::c_char, n: ::std::ffi::c_uint; userdata: ();| -> (*const ::std::ffi::c_char, ::std::ffi::c_uint) {
+            |start: *const ::std::ffi::c_char, n: ::std::ffi::c_uint; userdata: ();| -> $crate::NixideResult<String> {
                 unsafe {
                     let retval = &raw mut (*userdata).retval;
-                    retval.write((start, n))
+                    retval.write($crate::stdext::CCharPtrExt::to_utf8_string_n(start, n as usize))
                 }
             },
             $function
         );
 
-        __result.and_then(|(start, n)| {
-            let __return = $crate::stdext::CCharPtrExt::to_utf8_string_n(start, n as usize);
-
-            __return
-        })
+        match __result {
+            Ok(res) => res,
+            Err(res) => Err(res),
+        }
     }};
 }
 pub(crate) use nix_string_callback;
 
 macro_rules! nix_pathbuf_callback {
-    ($function:expr $(,)?) => {{
-        $crate::util::wrap::nix_string_callback!($function).map(::std::path::PathBuf::from)
-    }};
+    ($function:expr $(,)?) => {{ $crate::util::wrap::nix_string_callback!($function).map(::std::path::PathBuf::from) }};
 }
 pub(crate) use nix_pathbuf_callback;