diff --git a/Cargo.lock b/Cargo.lock
index ff32633..9af7062 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -190,6 +190,7 @@ checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
 name = "nixide"
 version = "0.1.0"
 dependencies = [
+ "libc",
  "nixide-sys",
  "serial_test",
  "stdext",
diff --git a/nixide/Cargo.toml b/nixide/Cargo.toml
index e97d5fe..7a1b4e4 100644
--- a/nixide/Cargo.toml
+++ b/nixide/Cargo.toml
@@ -24,8 +24,9 @@ util = []
 gc = []
 
 [dependencies]
-nixide-sys = { path = "../nixide-sys", version = "0.1.0" }
+libc = "0.2.183"
 stdext = "0.3.3"
+nixide-sys = { path = "../nixide-sys", version = "0.1.0" }
 
 [dev-dependencies]
 serial_test = "3.4.0"
diff --git a/nixide/src/errors/error.rs b/nixide/src/errors/error.rs
index bcebcf8..29696f1 100644
--- a/nixide/src/errors/error.rs
+++ b/nixide/src/errors/error.rs
@@ -137,15 +137,15 @@ impl Display for NixideError {
     }
 }
 
-pub trait AsErr<T> {
-    fn as_err(self) -> Result<(), T>;
-}
+// pub trait AsErr<T> {
+//     fn as_err(self) -> Result<(), T>;
+// }
 
-impl AsErr<NixideError> for Option<NixideError> {
-    fn as_err(self) -> Result<(), NixideError> {
-        match self {
-            Some(err) => Err(err),
-            None => Ok(()),
-        }
-    }
-}
+// impl AsErr<NixideError> for Option<NixideError> {
+//     fn as_err(self) -> Result<(), NixideError> {
+//         match self {
+//             Some(err) => Err(err),
+//             None => Ok(()),
+//         }
+//     }
+// }
diff --git a/nixide/src/lib.rs b/nixide/src/lib.rs
index 05a1738..5b363b4 100644
--- a/nixide/src/lib.rs
+++ b/nixide/src/lib.rs
@@ -1,5 +1,9 @@
 // #![warn(missing_docs)]
 
+// #[allow(unused_extern_crates)]
+pub extern crate libc;
+pub extern crate nixide_sys as sys;
+
 pub(crate) mod errors;
 // mod expr;
 // mod flake;
@@ -15,8 +19,6 @@ pub use store::{Store, StorePath};
 pub use verbosity::NixVerbosity;
 pub use version::NixVersion;
 
-pub use nixide_sys as sys;
-
 /// Sets the verbosity level
 ///
 /// # Arguments
diff --git a/nixide/src/store/mod.rs b/nixide/src/store/mod.rs
index 7c057d7..0d52edb 100644
--- a/nixide/src/store/mod.rs
+++ b/nixide/src/store/mod.rs
@@ -23,7 +23,7 @@ use std::result::Result;
 
 use crate::errors::{new_nixide_error, ErrorContext};
 use crate::stdext::CCharPtrExt;
-use crate::util::wrap::{self, UserData};
+use crate::util::wrap;
 use crate::util::wrappers::AsInnerPtr;
 use crate::{NixideError, NixideResult};
 use nixide_sys as sys;
@@ -87,96 +87,42 @@ impl Store {
     pub fn realise<F>(
         &self,
         path: &StorePath,
-        callback: fn(&str, &StorePath),
-    ) -> NixideResult<(String, StorePath)> {
-        // // Type alias for our userdata: (outputs vector, context)
-        // type Userdata = (
-        //     Vec<(String, StorePath)>,
-        //     Arc<ErrorContext>,
-        //     fn(&str, &StorePath),
-        // );
-        //
-        // // Callback function that will be called for each realized output
-        // unsafe extern "C" fn realise_callback(
-        //     userdata: *mut c_void,
-        //     out_name_ptr: *const c_char,
-        //     out_path_ptr: *const sys::StorePath,
-        // ) {
-        //     // SAFETY: userdata is a valid pointer to our (Vec, Arc<Context>) tuple
-        //     let (outputs, ctx, callback) = unsafe { &mut *(userdata as *mut Userdata) };
-        //
-        //     // SAFETY: outname is a valid C string from Nix
-        //     let output_name = if !out_name_ptr.is_null() {
-        //         unsafe { CStr::from_ptr(out_name_ptr).to_string_lossy().into_owned() }
-        //     } else {
-        //         String::from("out") // Default output name
-        //     };
-        //
-        //     // SAFETY: out is a valid StorePath pointer from Nix, we need to clone it
-        //     // because Nix owns the original and may free it after the callback
-        //     if !out_path_ptr.is_null() {
-        //         let cloned_path_ptr =
-        //             unsafe { sys::nix_store_path_clone(out_path_ptr as *mut sys::StorePath) };
-        //         if let Some(inner) = NonNull::new(cloned_path_ptr) {
-        //             let store_path = StorePath { inner };
-        //
-        //             callback(output_name.as_ref(), &store_path);
-        //
-        //             outputs.push((output_name, store_path));
-        //         }
-        //     }
-        // }
-        //
-        // // Create userdata with empty outputs vector and context
-        // let mut userdata: Userdata = (Vec::new(), Arc::new(ErrorContext::new()), callback);
-        // let userdata_ptr = &mut userdata as *mut Userdata as *mut std::os::raw::c_void;
-        //
-        // // SAFETY: All pointers are valid, callback is compatible with the FFI signature
-        // // - self._context is valid for the duration of this call
-        // // - self.inner is valid (checked in Store::open)
-        // // - path.inner is valid (checked in StorePath::parse)
-        // // - userdata_ptr points to valid stack memory
-        // // - realize_callback matches the expected C function signature
-        // let err = unsafe {
-        //     sys::nix_store_realise(
-        //         ctx.as_ptr(),
-        //         self.inner.as_ptr(),
-        //         path.as_ptr(),
-        //         userdata_ptr,
-        //         Some(realise_callback),
-        //     )
-        // };
-
+        user_callback: fn(&str, &StorePath),
+    ) -> NixideResult<Vec<(String, StorePath)>> {
         wrap::nix_callback!(
             |; userdata: fn(&str, &StorePath);
              output_name_ptr: *const c_char,
              output_path_ptr: *const sys::StorePath|
-             -> NixideResult<(String, StorePath)> {
+             -> Vec<(String, StorePath)> {
                 // XXX: TODO: test to see if this is ever null ("out" as a default feels unsafe...)
-                // let output_name = output_name_ptr.to_utf8_string().unwrap_or("out".to_owned());
                 // NOTE: this also ensures `output_name_ptr` isn't null
-                let output_name = output_name_ptr.to_utf8_string()?;
+                let output_name = output_name_ptr.to_utf8_string().expect("IDK1");
 
                 let inner = wrap::nix_ptr_fn!(|ctx| unsafe {
                     sys::nix_store_path_clone(output_path_ptr as *mut sys::StorePath)
-                })?;
+                }).expect("IDK2");
                 let store_path = StorePath { inner };
 
                 let callback = unsafe { (*userdata).inner };
                 callback(output_name.as_ref(), &store_path);
 
-                Ok((output_name, store_path))
+                (output_name, store_path);
             },
             |callback,
-             state: *mut UserData<fn(&str, &StorePath), NixideResult<(String, StorePath)>>,
+             state: *mut __UserData,
              ctx: &ErrorContext| unsafe {
+                // register userdata
+                // WARNING: Using `write` instead of assignment via `=`
+                // WARNING: to not call `drop` on the old, uninitialized value.
+                (&raw mut (*state).inner).write(user_callback);
+
                 sys::nix_store_realise(
                     ctx.as_ptr(),
                     self.inner.as_ptr(),
                     path.as_ptr(),
                     (*state).inner_ptr() as *mut c_void,
                     Some(callback),
-                )
+                );
             }
         )
     }
diff --git a/nixide/src/store/tests.rs b/nixide/src/store/tests.rs
index d0b7744..da72ae7 100644
--- a/nixide/src/store/tests.rs
+++ b/nixide/src/store/tests.rs
@@ -16,9 +16,6 @@ fn test_store_opening() {
         sys::nix_libstore_init(ctx.as_ptr());
         ctx.pop()
             .expect("nix_libstore_init failed with bad ErrorContext");
-        sys::nix_libexpr_init(ctx.as_ptr());
-        ctx.pop()
-            .expect("nix_libexpr_init failed with bad ErrorContext");
     };
 
     let _store = Store::open(None).expect("Failed to open store");
@@ -35,9 +32,6 @@ fn test_store_path_parse() {
         sys::nix_libstore_init(ctx.as_ptr());
         ctx.pop()
             .expect("nix_libstore_init failed with bad ErrorContext");
-        sys::nix_libexpr_init(ctx.as_ptr());
-        ctx.pop()
-            .expect("nix_libexpr_init failed with bad ErrorContext");
     };
 
     let store = Store::open(None).expect("Failed to open store");
@@ -58,9 +52,6 @@ fn test_store_path_clone() {
         sys::nix_libstore_init(ctx.as_ptr());
         ctx.pop()
             .expect("nix_libstore_init failed with bad ErrorContext");
-        sys::nix_libexpr_init(ctx.as_ptr());
-        ctx.pop()
-            .expect("nix_libexpr_init failed with bad ErrorContext");
     };
 
     let store = Store::open(None).expect("Failed to open store");
diff --git a/nixide/src/util/panic.rs b/nixide/src/util/panic.rs
index 51f2f34..b9e5e95 100644
--- a/nixide/src/util/panic.rs
+++ b/nixide/src/util/panic.rs
@@ -9,10 +9,10 @@ macro_rules! panic_issue {
 
 macro_rules! panic_issue_call_failed {
     () => {{
-        crate::util::panic_issue!("[nixide] call to `{}` failed", stdext::debug_name!())
+        crate::util::panic_issue!("[nixide] call to `{}` failed", $crate::stdext::debug_name!())
     }};
     ($($arg:expr),*) => {{
-        crate::util::panic_issue!("[nixide] call to `{}` failed with \"{}\"", stdext::debug_name!(), format!($($arg),*))
+        crate::util::panic_issue!("[nixide] call to `{}` failed with \"{}\"", $crate::stdext::debug_name!(), format!($($arg),*))
     }};
 }
 
diff --git a/nixide/src/util/wrap.rs b/nixide/src/util/wrap.rs
index 595511b..33790c9 100644
--- a/nixide/src/util/wrap.rs
+++ b/nixide/src/util/wrap.rs
@@ -4,6 +4,8 @@ pub(crate) struct UserData<S, T> {
     pub inner: S,
     pub retval: T,
 
+    // XXX: TODO: write impl functions to set and get these values,
+    // XXX: TODO: and another one to unwrap a `MaybeUninit<UserData<S, T>>`
     #[cfg(debug_assertions)]
     pub init_inner: bool,
 
@@ -18,14 +20,6 @@ impl<S, T> AsMut<UserData<S, T>> for UserData<S, T> {
 }
 
 impl<S, T> UserData<S, T> {
-    /// # Warning
-    ///
-    /// Ensure `self.retval` has been initialised before unwrapping!
-    ///
-    // pub unsafe fn unwrap(self) -> (S, T) {
-    //     (self.inner, self.retval)
-    // }
-
     pub unsafe fn as_mut_ptr(&mut self) -> *mut Self {
         self as *mut Self
     }
@@ -36,10 +30,6 @@ impl<S, T> UserData<S, T> {
             &raw mut (*ptr).inner
         }
     }
-
-    // pub unsafe fn retval_ptr(&mut self) -> *mut c_void {
-    //     &mut self.retval as *mut T as *mut c_void
-    // }
 }
 
 macro_rules! nonnull {
@@ -73,42 +63,27 @@ macro_rules! nix_ptr_fn {
 }
 pub(crate) use nix_ptr_fn;
 
-macro_rules! __nix_callback {
-    ($userdata_type:ty, $ret:ty, $callback:expr) => {{
-        let mut __ctx = $crate::errors::ErrorContext::new();
-        let mut __state: ::std::mem::MaybeUninit<__UserData> = ::std::mem::MaybeUninit::uninit();
-
-        $callback(__wrapper_callback, __state.as_mut_ptr(), &__ctx);
-
-        // add type annotations for compiler
-        let __return: $ret = __ctx
-            .pop()
-            .and_then(|_| unsafe { __state.assume_init().retval });
-        __return
-    }};
-}
-#[allow(unused_imports)] // XXX: TODO: replace the tail of `nix_callback!` with this macro
-pub(crate) use __nix_callback;
-
 /// `libnix` functions consistently either expect the `userdata`/`user_data` (inconsistently named in the API...)
 /// field to be the first or last parameter (differs between function). The `nix_callback!` macro allows the
 /// position to be specified by either the following syntax:
 ///
 /// ```rs
-/// nix_callback(userdata; ...); // first parameter
-/// nix_callback(...; userdata); // last parameter
+/// nix_callback!(; userdata; ...); // first parameter
+/// nix_callback!(...; userdata; ); // last parameter
 /// ```
 ///
 macro_rules! nix_callback {
     ( | $( $($pre:ident : $pre_ty:ty),+ $(,)? )? ; $userdata:ident : $userdata_type:ty ; $( $($post:ident : $post_ty:ty),+ $(,)? )? | -> $ret:ty $body:block, $function:expr $(,)? ) => {{
         type __UserData = $crate::util::wrap::UserData<$userdata_type, $ret>;
         // create a function item that wraps the closure body (so it has a concrete type)
+        // WARNING: this function must have no return type, use the `UserData.inner`
+        // WARNING: field instead as an `out` pointer.
         #[allow(unused_variables)]
         unsafe extern "C" fn __captured_fn(
             $($( $pre: $pre_ty, )*)?
             $userdata: *mut __UserData,
             $($( $post: $post_ty, )*)?
-        ) -> $ret { $body }
+        ) { $body }
 
         unsafe extern "C" fn __wrapper_callback(
             $($( $pre: $pre_ty, )*)?
@@ -116,17 +91,12 @@ macro_rules! nix_callback {
             $($( $post: $post_ty, )*)?
         ) {
             unsafe {
-                let userdata_ = $userdata as *mut __UserData;
-                let stored_retval = &raw mut (*userdata_).retval;
-
-                let retval =
-                    __captured_fn(
-                        $($( $pre, )*)?
-                        userdata_,
-                        $($( $post, )*)?
-                    );
-
-                stored_retval.write(retval)
+                __captured_fn(
+                    $($( $pre, )*)?
+                    // userdata_,
+                    $userdata as *mut __UserData,
+                    $($( $post, )*)?
+                );
             }
         }
 
@@ -136,21 +106,35 @@ macro_rules! nix_callback {
         $function(__wrapper_callback, __state.as_mut_ptr(), &__ctx);
 
         // type annotations for compiler
-        let __result: $ret = __ctx.pop().and_then(|_| unsafe { __state.assume_init().retval });
-        __result
+        let __return: $crate::NixideResult<$ret> = __ctx.pop().and_then(|_| ::std::result::Result::Ok(unsafe { __state.assume_init().retval }));
+        __return
     }};
 }
 pub(crate) use nix_callback;
 
-// XXX: TODO: convert these to declarative macros
 macro_rules! nix_string_callback {
     ($function:expr $(,)?) => {{
-        $crate::util::wrap::nix_callback!(
-            |start: *const ::std::ffi::c_char, n: ::std::ffi::c_uint; userdata: ();| -> $crate::NixideResult<String> {
-                $crate::stdext::CCharPtrExt::to_utf8_string_n(start, n as usize)
+        #[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) {
+                unsafe {
+                    let retval = &raw mut (*userdata).retval;
+                    retval.write((start, n))
+                }
             },
             $function
-        )
+        );
+
+        __result.and_then(|(start, n)| {
+            let __return = $crate::stdext::CCharPtrExt::to_utf8_string_n(start, n as usize);
+
+            __return
+        })
     }};
 }
 pub(crate) use nix_string_callback;
diff --git a/nixide/src/util/wrappers.rs b/nixide/src/util/wrappers.rs
index 829437a..ab43cce 100644
--- a/nixide/src/util/wrappers.rs
+++ b/nixide/src/util/wrappers.rs
@@ -1,17 +1,23 @@
-use crate::NixideError;
-
-pub trait AsErr<T> {
-    fn as_err(self) -> Result<(), T>;
-}
-
-impl AsErr<NixideError> for Option<NixideError> {
-    fn as_err(self) -> Result<(), NixideError> {
-        match self {
-            Some(err) => Err(err),
-            None => Ok(()),
-        }
-    }
-}
+// use crate::NixideError;
+//
+// pub trait AsErr<T> {
+//     fn as_err(self) -> Result<(), T>;
+// }
+//
+// impl AsErr<NixideError> for Option<NixideError> {
+//     fn as_err(self) -> Result<(), NixideError> {
+//         match self {
+//             Some(err) => Err(err),
+//             None => Ok(()),
+//         }
+//     }
+// }
+//
+// pub trait FromC<T> {
+//     /// Creates a new instance of [Self] from the underlying
+//     /// libnix C type [T].
+//     unsafe fn from_c(value: T) -> Self;
+// }
 
 pub trait AsInnerPtr<T> {
     /// Get a pointer to the underlying (`inner`) `libnix` C struct.
@@ -23,9 +29,3 @@ pub trait AsInnerPtr<T> {
     /// in `unsafe` blocks for clarity.
     unsafe fn as_ptr(&self) -> *mut T;
 }
-
-pub trait FromC<T> {
-    /// Creates a new instance of [Self] from the underlying
-    /// libnix C type [T].
-    unsafe fn from_c(value: T) -> Self;
-}