diff --git a/tests/attribute_doc_comments/expected.md b/tests/attribute_doc_comments/expected.md
index 9ef4304..7777b75 100644
--- a/tests/attribute_doc_comments/expected.md
+++ b/tests/attribute_doc_comments/expected.md
@@ -19,15 +19,29 @@ pub mod trinitrix {
     }
 }
 /* C API */
-pub mod trinitrix_c {}
+pub mod trinitrix_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+}
 #[no_mangle]
 pub extern "C" fn trinitrix_hi(
     output: *mut trixy::types::String,
-    name: String,
+    name: trixy::types::String,
 ) -> core::ffi::c_int {
     let output_val: trixy::types::String = {
         let (tx, rx) = trixy::oneshot::channel();
-        callback_function(trinitrix_hi);
+        callback_function(
+            Commands::Trinitrix(crate::trinitrix::Trinitrix::hi {
+                trixy_output: tx,
+                name: match name.try_into() {
+                    Ok(ok) => ok,
+                    Err(err) => {
+                        trixy::types::traits::errno::set(err.into());
+                        return 0;
+                    }
+                },
+            }),
+        );
         let recv = rx
             .recv()
             .expect("The channel should not be closed until this value is received");
diff --git a/tests/doc_comments/expected.md b/tests/doc_comments/expected.md
index ec849a5..ff803d5 100644
--- a/tests/doc_comments/expected.md
+++ b/tests/doc_comments/expected.md
@@ -19,15 +19,29 @@ pub mod trinitrix {
     }
 }
 /* C API */
-pub mod trinitrix_c {}
+pub mod trinitrix_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+}
 #[no_mangle]
 pub extern "C" fn trinitrix_hi(
     output: *mut trixy::types::String,
-    name: String,
+    name: trixy::types::String,
 ) -> core::ffi::c_int {
     let output_val: trixy::types::String = {
         let (tx, rx) = trixy::oneshot::channel();
-        callback_function(trinitrix_hi);
+        callback_function(
+            Commands::Trinitrix(crate::trinitrix::Trinitrix::hi {
+                trixy_output: tx,
+                name: match name.try_into() {
+                    Ok(ok) => ok,
+                    Err(err) => {
+                        trixy::types::traits::errno::set(err.into());
+                        return 0;
+                    }
+                },
+            }),
+        );
         let recv = rx
             .recv()
             .expect("The channel should not be closed until this value is received");
diff --git a/tests/empty_doc_comment/expected.md b/tests/empty_doc_comment/expected.md
index 767bc77..14e86f2 100644
--- a/tests/empty_doc_comment/expected.md
+++ b/tests/empty_doc_comment/expected.md
@@ -17,7 +17,10 @@ pub mod test {
     pub enum Test {}
 }
 /* C API */
-pub mod test_c {}
+pub mod test_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+}
 // vim: filetype=rust
 ```
 
diff --git a/tests/functions/expected.md b/tests/functions/expected.md
index 96c0e2f..30b7ac4 100644
--- a/tests/functions/expected.md
+++ b/tests/functions/expected.md
@@ -9,7 +9,9 @@ File path: `out/dir/api.rs`
 pub enum Commands {
     /// Call out an outstanding person
     #[allow(non_camel_case_types)]
-    call_me_back_outstanding { callback: fn(String) -> String },
+    call_me_back_outstanding {
+        callback: extern "C" fn(trixy::types::String) -> trixy::types::String,
+    },
     One(one::One),
 }
 pub mod one {
@@ -17,21 +19,44 @@ pub mod one {
     pub enum One {
         /// Call out a person
         #[allow(non_camel_case_types)]
-        call_me_back { callback: fn(u32) },
+        call_me_back { callback: extern "C" fn(trixy::types::u32) },
     }
 }
 /* C API */
 #[no_mangle]
 pub extern "C" fn call_me_back_outstanding(
-    callback: fn(String) -> String,
+    callback: extern "C" fn(trixy::types::String) -> trixy::types::String,
 ) -> core::ffi::c_int {
-    callback_function(call_me_back_outstanding);
+    callback_function(crate::Commands::call_me_back_outstanding {
+        callback: match callback.try_into() {
+            Ok(ok) => ok,
+            Err(err) => {
+                trixy::types::traits::errno::set(err.into());
+                return 0;
+            }
+        },
+    });
     return 1;
 }
-pub mod one_c {}
+pub mod one_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+}
 #[no_mangle]
-pub extern "C" fn one_call_me_back(callback: fn(u32)) -> core::ffi::c_int {
-    callback_function(one_call_me_back);
+pub extern "C" fn one_call_me_back(
+    callback: extern "C" fn(trixy::types::u32),
+) -> core::ffi::c_int {
+    callback_function(
+        crate::Commands::One(crate::one::One::call_me_back {
+            callback: match callback.try_into() {
+                Ok(ok) => ok,
+                Err(err) => {
+                    trixy::types::traits::errno::set(err.into());
+                    return 0;
+                }
+            },
+        }),
+    );
     return 1;
 }
 // vim: filetype=rust
@@ -61,7 +86,7 @@ extern int one_call_me_back (void (*callback) (uint32_t));
 
 struct one
 {
-  int (*call_me_back) ();
+  int (*call_me_back) (void (*callback) (uint32_t));
 };
 
 const struct one one = {
diff --git a/tests/multi_line_doc_comment/expected.md b/tests/multi_line_doc_comment/expected.md
index 42386a6..3544702 100644
--- a/tests/multi_line_doc_comment/expected.md
+++ b/tests/multi_line_doc_comment/expected.md
@@ -22,15 +22,29 @@ pub mod trinitrix {
     }
 }
 /* C API */
-pub mod trinitrix_c {}
+pub mod trinitrix_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+}
 #[no_mangle]
 pub extern "C" fn trinitrix_hi(
     output: *mut trixy::types::String,
-    name: String,
+    name: trixy::types::String,
 ) -> core::ffi::c_int {
     let output_val: trixy::types::String = {
         let (tx, rx) = trixy::oneshot::channel();
-        callback_function(trinitrix_hi);
+        callback_function(
+            Commands::Trinitrix(crate::trinitrix::Trinitrix::hi {
+                trixy_output: tx,
+                name: match name.try_into() {
+                    Ok(ok) => ok,
+                    Err(err) => {
+                        trixy::types::traits::errno::set(err.into());
+                        return 0;
+                    }
+                },
+            }),
+        );
         let recv = rx
             .recv()
             .expect("The channel should not be closed until this value is received");
diff --git a/tests/trinitrix_api/expected.md b/tests/trinitrix_api/expected.md
index cc6af7d..5d50051 100644
--- a/tests/trinitrix_api/expected.md
+++ b/tests/trinitrix_api/expected.md
@@ -12,7 +12,7 @@ pub enum Commands {
 pub mod trinitrix {
     #[derive(Debug)]
     pub enum Trinitrix {
-        Std(std::Std),
+        Stdi(stdi::Stdi),
         Api(api::Api),
     }
     /// Language specific functions, which mirror the `trinitrix.api` namespace.
@@ -20,9 +20,9 @@ pub mod trinitrix {
     /// one as it will most likely be more high-level and easier to use (as it isn't abstracted
     /// over multiple languages). Feel free to drop down to the lower level api, if you feel
     /// like that more, it should be as stable and user-oriented as the `std` functions
-    pub mod std {
+    pub mod stdi {
         #[derive(Debug)]
-        pub enum Std {}
+        pub enum Stdi {}
     }
     /// General API to change stuff in Trinitrix
     pub mod api {
@@ -54,9 +54,9 @@ pub mod trinitrix {
             impl From<crate::trinitrix_c::api_c::ui_c::Mode_c> for Mode {
                 fn from(value: crate::trinitrix_c::api_c::ui_c::Mode_c) -> Self {
                     match value {
-                        Mode_c::Normal => Self::Normal,
-                        Mode_c::Insert => Self::Insert,
-                        Mode_c::Command => Self::Command,
+                        crate::trinitrix_c::api_c::ui_c::Mode_c::Normal => Self::Normal,
+                        crate::trinitrix_c::api_c::ui_c::Mode_c::Insert => Self::Insert,
+                        crate::trinitrix_c::api_c::ui_c::Mode_c::Command => Self::Command,
                     }
                 }
             }
@@ -105,7 +105,7 @@ pub mod trinitrix {
             pub enum Keymaps {
                 /// Add a new keymapping
                 #[allow(non_camel_case_types)]
-                add { mode: String, key: String, callback: fn() },
+                add { mode: String, key: String, callback: extern "C" fn() },
                 /// Remove a keymapping
                 ///
                 /// Does nothing, if the keymapping doesn't exists yet
@@ -147,104 +147,279 @@ pub mod trinitrix {
     }
 }
 /* C API */
-pub mod trinitrix_c {}
-pub mod std_c {}
-pub mod api_c {}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_exit() -> core::ffi::c_int {
-    callback_function(trinitrix_api_exit);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_room_message_send(message: String) -> core::ffi::c_int {
-    callback_function(trinitrix_api_room_message_send);
-    return 1;
-}
-pub mod ui_c {
-    #[allow(non_camel_case_types)]
-    #[repr(C)]
-    #[derive(Debug)]
-    pub enum Mode_c {
-        /// Default mode (navigation mode)
-        Normal,
-        /// Allows you to insert things
-        Insert,
-        /// actives the command line
-        Command,
+pub mod trinitrix_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+    pub mod stdi_c {
+        #[allow(unused_imports)]
+        use crate::callback_function;
     }
-    impl From<crate::trinitrix::api::ui::Mode> for Mode_c {
-        fn from(value: crate::trinitrix::api::ui::Mode) -> Self {
-            match value {
-                Mode::Normal => Self::Normal,
-                Mode::Insert => Self::Insert,
-                Mode::Command => Self::Command,
+    pub mod api_c {
+        #[allow(unused_imports)]
+        use crate::callback_function;
+        pub mod ui_c {
+            #[allow(unused_imports)]
+            use crate::callback_function;
+            #[allow(non_camel_case_types)]
+            #[repr(C)]
+            #[derive(Debug)]
+            pub enum Mode_c {
+                /// Default mode (navigation mode)
+                Normal,
+                /// Allows you to insert things
+                Insert,
+                /// actives the command line
+                Command,
+            }
+            impl From<crate::trinitrix::api::ui::Mode> for Mode_c {
+                fn from(value: crate::trinitrix::api::ui::Mode) -> Self {
+                    match value {
+                        crate::trinitrix::api::ui::Mode::Normal => Self::Normal,
+                        crate::trinitrix::api::ui::Mode::Insert => Self::Insert,
+                        crate::trinitrix::api::ui::Mode::Command => Self::Command,
+                    }
+                }
             }
         }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_ui_set_mode(
+            mode: crate::trinitrix_c::api_c::ui_c::Mode_c,
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Ui(crate::trinitrix::api::ui::Ui::set_mode {
+                            mode: match mode.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_ui_cycle_planes() -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Ui(
+                            crate::trinitrix::api::ui::Ui::cycle_planes,
+                        ),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_ui_cycle_planes_rev() -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Ui(
+                            crate::trinitrix::api::ui::Ui::cycle_planes_rev,
+                        ),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        pub mod keymaps_c {
+            #[allow(unused_imports)]
+            use crate::callback_function;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_keymaps_add(
+            mode: trixy::types::String,
+            key: trixy::types::String,
+            callback: extern "C" fn(),
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Keymaps(crate::trinitrix::api::keymaps::Keymaps::add {
+                            mode: match mode.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                            key: match key.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                            callback: match callback.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_keymaps_remove(
+            mode: trixy::types::String,
+            key: trixy::types::String,
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Keymaps(crate::trinitrix::api::keymaps::Keymaps::remove {
+                            mode: match mode.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                            key: match key.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_keymaps_get(
+            mode: trixy::types::String,
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Keymaps(crate::trinitrix::api::keymaps::Keymaps::get {
+                            mode: match mode.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        pub mod raw_c {
+            #[allow(unused_imports)]
+            use crate::callback_function;
+            pub mod __private_c {
+                #[allow(unused_imports)]
+                use crate::callback_function;
+            }
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_raw_raise_error(
+            error_message: trixy::types::String,
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Raw(crate::trinitrix::api::raw::Raw::raise_error {
+                            error_message: match error_message.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_raw_display_output(
+            output_message: trixy::types::String,
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Raw(crate::trinitrix::api::raw::Raw::display_output {
+                            output_message: match output_message.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+        #[no_mangle]
+        pub extern "C" fn trinitrix_api_raw_send_input_unprocessed(
+            input: trixy::types::String,
+        ) -> core::ffi::c_int {
+            callback_function(
+                crate::Commands::Trinitrix(
+                    crate::trinitrix::Trinitrix::Api(
+                        crate::trinitrix::api::Api::Raw(crate::trinitrix::api::raw::Raw::send_input_unprocessed {
+                            input: match input.try_into() {
+                                Ok(ok) => ok,
+                                Err(err) => {
+                                    trixy::types::traits::errno::set(err.into());
+                                    return 0;
+                                }
+                            },
+                        }),
+                    ),
+                ),
+            );
+            return 1;
+        }
+    }
+    #[no_mangle]
+    pub extern "C" fn trinitrix_api_exit() -> core::ffi::c_int {
+        callback_function(
+            crate::Commands::Trinitrix(
+                crate::trinitrix::Trinitrix::Api(crate::trinitrix::api::Api::exit),
+            ),
+        );
+        return 1;
+    }
+    #[no_mangle]
+    pub extern "C" fn trinitrix_api_room_message_send(
+        message: trixy::types::String,
+    ) -> core::ffi::c_int {
+        callback_function(
+            crate::Commands::Trinitrix(
+                crate::trinitrix::Trinitrix::Api(crate::trinitrix::api::Api::room_message_send {
+                    message: match message.try_into() {
+                        Ok(ok) => ok,
+                        Err(err) => {
+                            trixy::types::traits::errno::set(err.into());
+                            return 0;
+                        }
+                    },
+                }),
+            ),
+        );
+        return 1;
     }
 }
-#[no_mangle]
-pub extern "C" fn trinitrix_api_ui_set_mode(
-    mode: crate::trinitrix::api::ui::Mode,
-) -> core::ffi::c_int {
-    callback_function(trinitrix_api_ui_set_mode);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_ui_cycle_planes() -> core::ffi::c_int {
-    callback_function(trinitrix_api_ui_cycle_planes);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_ui_cycle_planes_rev() -> core::ffi::c_int {
-    callback_function(trinitrix_api_ui_cycle_planes_rev);
-    return 1;
-}
-pub mod keymaps_c {}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_keymaps_add(
-    mode: String,
-    key: String,
-    callback: fn(),
-) -> core::ffi::c_int {
-    callback_function(trinitrix_api_keymaps_add);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_keymaps_remove(
-    mode: String,
-    key: String,
-) -> core::ffi::c_int {
-    callback_function(trinitrix_api_keymaps_remove);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_keymaps_get(mode: String) -> core::ffi::c_int {
-    callback_function(trinitrix_api_keymaps_get);
-    return 1;
-}
-pub mod raw_c {}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_raw_raise_error(
-    error_message: String,
-) -> core::ffi::c_int {
-    callback_function(trinitrix_api_raw_raise_error);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_raw_display_output(
-    output_message: String,
-) -> core::ffi::c_int {
-    callback_function(trinitrix_api_raw_display_output);
-    return 1;
-}
-#[no_mangle]
-pub extern "C" fn trinitrix_api_raw_send_input_unprocessed(
-    input: String,
-) -> core::ffi::c_int {
-    callback_function(trinitrix_api_raw_send_input_unprocessed);
-    return 1;
-}
-pub mod __private_c {}
 // vim: filetype=rust
 ```
 
@@ -347,7 +522,7 @@ extern int trinitrix_api_raw_send_input_unprocessed (const char *input);
  * the lower level api, if you feel like that more, it should be as stable and
  * user-oriented as the `std` functions
  */
-struct std
+struct stdi
 {
 };
 
@@ -356,7 +531,7 @@ struct std
  */
 struct ui
 {
-  int (*set_mode) ();
+  int (*set_mode) (enum Mode);
   int (*cycle_planes) (void);
   int (*cycle_planes_rev) (void);
 };
@@ -392,9 +567,9 @@ struct ui
  */
 struct keymaps
 {
-  int (*add) ();
-  int (*remove) ();
-  int (*get) ();
+  int (*add) (const char *, const char *, void (*callback) ());
+  int (*remove) (const char *, const char *);
+  int (*get) (const char *);
 };
 
 /**
@@ -413,9 +588,9 @@ struct __private
  */
 struct raw
 {
-  int (*raise_error) ();
-  int (*display_output) ();
-  int (*send_input_unprocessed) ();
+  int (*raise_error) (const char *);
+  int (*display_output) (const char *);
+  int (*send_input_unprocessed) (const char *);
   struct __private __private;
 };
 
@@ -425,7 +600,7 @@ struct raw
 struct api
 {
   int (*exit) (void);
-  int (*room_message_send) ();
+  int (*room_message_send) (const char *);
   struct ui ui;
   struct keymaps keymaps;
   struct raw raw;
@@ -433,11 +608,11 @@ struct api
 
 struct trinitrix
 {
-  struct std std;
+  struct stdi stdi;
   struct api api;
 };
 
-const struct std std = {};
+const struct stdi stdi = {};
 const struct ui ui = {
   .set_mode = trinitrix_api_ui_set_mode,
   .cycle_planes = trinitrix_api_ui_cycle_planes,
@@ -463,7 +638,7 @@ const struct api api = {
   .raw = raw,
 };
 const struct trinitrix trinitrix = {
-  .std = std,
+  .stdi = stdi,
   .api = api,
 };
 
diff --git a/tests/trinitrix_api/input.tri b/tests/trinitrix_api/input.tri
index ea33579..8d7f6de 100644
--- a/tests/trinitrix_api/input.tri
+++ b/tests/trinitrix_api/input.tri
@@ -33,7 +33,7 @@ mod trinitrix {
     /// one as it will most likely be more high-level and easier to use (as it isn't abstracted
     /// over multiple languages). Feel free to drop down to the lower level api, if you feel
     /// like that more, it should be as stable and user-oriented as the `std` functions
-    mod std {}
+    mod stdi {}
 
     /// General API to change stuff in Trinitrix
     mod api {
diff --git a/tests/types/expected.md b/tests/types/expected.md
index cdb3f0a..3e56d91 100644
--- a/tests/types/expected.md
+++ b/tests/types/expected.md
@@ -15,7 +15,7 @@ pub mod test {
     #[derive(Debug)]
     pub struct Callback {
         /// Very important field
-        pub func: fn(String) -> String,
+        pub func: extern "C" fn(trixy::types::String) -> trixy::types::String,
         /// Very important field for keeping time constant
         pub timeout: u32,
     }
@@ -58,9 +58,9 @@ pub mod test {
     impl From<crate::test_c::CallbackPriority_c> for CallbackPriority {
         fn from(value: crate::test_c::CallbackPriority_c) -> Self {
             match value {
-                CallbackPriority_c::High => Self::High,
-                CallbackPriority_c::Medium => Self::Medium,
-                CallbackPriority_c::Low => Self::Low,
+                crate::test_c::CallbackPriority_c::High => Self::High,
+                crate::test_c::CallbackPriority_c::Medium => Self::Medium,
+                crate::test_c::CallbackPriority_c::Low => Self::Low,
             }
         }
     }
@@ -75,6 +75,8 @@ pub mod test {
 }
 /* C API */
 pub mod test_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
     /// Same thing as above (and a enum doc comment test)
     #[allow(non_camel_case_types)]
     #[repr(C)]
@@ -92,9 +94,9 @@ pub mod test_c {
     impl From<crate::test::CallbackPriority> for CallbackPriority_c {
         fn from(value: crate::test::CallbackPriority) -> Self {
             match value {
-                CallbackPriority::High => Self::High,
-                CallbackPriority::Medium => Self::Medium,
-                CallbackPriority::Low => Self::Low,
+                crate::test::CallbackPriority::High => Self::High,
+                crate::test::CallbackPriority::Medium => Self::Medium,
+                crate::test::CallbackPriority::Low => Self::Low,
             }
         }
     }
@@ -104,17 +106,43 @@ pub mod test_c {
     #[derive(Debug)]
     pub struct Callback_c {
         /// Very important field
-        pub func: fn(String) -> String,
+        pub func: extern "C" fn(trixy::types::String) -> trixy::types::String,
         /// Very important field for keeping time constant
         pub timeout: trixy::types::u32,
     }
+    impl TryFrom<crate::test::Callback> for Callback_c {
+        type Error = trixy::types::error::TypeConversionError;
+        fn try_from(value: crate::test::Callback) -> Result<Self, Self::Error> {
+            Ok(Self {
+                func: value.func.try_into()?,
+                timeout: value.timeout.try_into()?,
+            })
+        }
+    }
 }
 #[no_mangle]
 pub extern "C" fn test_execute_callback(
-    callback: crate::test::Callback,
-    priority: crate::test::CallbackPriority,
+    callback: crate::test_c::Callback_c,
+    priority: crate::test_c::CallbackPriority_c,
 ) -> core::ffi::c_int {
-    callback_function(test_execute_callback);
+    callback_function(
+        crate::Commands::Test(crate::test::Test::execute_callback {
+            callback: match callback.try_into() {
+                Ok(ok) => ok,
+                Err(err) => {
+                    trixy::types::traits::errno::set(err.into());
+                    return 0;
+                }
+            },
+            priority: match priority.try_into() {
+                Ok(ok) => ok,
+                Err(err) => {
+                    trixy::types::traits::errno::set(err.into());
+                    return 0;
+                }
+            },
+        }),
+    );
     return 1;
 }
 // vim: filetype=rust
@@ -173,7 +201,7 @@ extern int test_execute_callback (struct Callback callback,
 
 struct test
 {
-  int (*execute_callback) ();
+  int (*execute_callback) (struct Callback, enum CallbackPriority);
 };
 
 const struct test test = {
diff --git a/tests/utf8_in_doc_comment/expected.md b/tests/utf8_in_doc_comment/expected.md
index 2c02e9f..1c80c5d 100644
--- a/tests/utf8_in_doc_comment/expected.md
+++ b/tests/utf8_in_doc_comment/expected.md
@@ -17,7 +17,10 @@ pub mod trinitrix {
     pub enum Trinitrix {}
 }
 /* C API */
-pub mod trinitrix_c {}
+pub mod trinitrix_c {
+    #[allow(unused_imports)]
+    use crate::callback_function;
+}
 // vim: filetype=rust
 ```