diff --git a/csbindgen-tests/src/lib.rs b/csbindgen-tests/src/lib.rs
index be42290..2ce0ac4 100644
--- a/csbindgen-tests/src/lib.rs
+++ b/csbindgen-tests/src/lib.rs
@@ -14,6 +14,28 @@ mod lz4;
 #[allow(non_camel_case_types)]
 mod lz4_ffi;
 
+#[no_mangle]
+pub extern "C" fn callback_test(cb: extern "C" fn(a: i32) -> i32) -> i32 {
+    cb(100)
+}
+
+#[no_mangle]
+pub extern "C" fn nullable_callback_test(cb: Option<extern "C" fn(a: i32) -> i32>) -> i32 {
+    match cb {
+        Some(f) => f(100),
+        None => -1,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn callback_test2() -> extern "C" fn(a: i32) -> i32 {
+    callback
+}
+
+extern "C" fn callback(a: i32) -> i32 {
+    a * a
+}
+
 #[no_mangle]
 #[allow(improper_ctypes_definitions)]
 pub extern "C" fn ignore_nop() -> (i32, i32) {
@@ -31,12 +53,6 @@ pub extern "C" fn my_add(x: i32, y: i32) -> i32 {
     x + y
 }
 
-#[no_mangle]
-pub extern "C" fn callback_test(cb: extern fn(a: i32) -> i32) -> i32 {
-    // Fn
-    cb(100)
-}
-
 #[no_mangle]
 pub extern "C" fn create_counter_context() -> *mut c_void {
     let ctx = Box::new(CounterContext {
diff --git a/csbindgen/src/emitter.rs b/csbindgen/src/emitter.rs
index 8c90036..5fe7657 100644
--- a/csbindgen/src/emitter.rs
+++ b/csbindgen/src/emitter.rs
@@ -25,7 +25,7 @@ pub fn emit_rust_method(list: &Vec<ExternMethod>, options: &BindgenOptions) -> S
                 format!(
                     "    {}: {}",
                     p.name,
-                    p.rust_type.to_string(method_type_path)
+                    p.rust_type.to_rust_string(method_type_path)
                 )
             })
             .collect::<Vec<_>>()
@@ -33,7 +33,7 @@ pub fn emit_rust_method(list: &Vec<ExternMethod>, options: &BindgenOptions) -> S
 
         let return_line = match &item.return_type {
             None => "".to_string(),
-            Some(v) => format!(" -> {}", v.to_string(method_type_path)),
+            Some(v) => format!(" -> {}", v.to_rust_string(method_type_path)),
         };
 
         let parameter_only_names = item
diff --git a/csbindgen/src/parser.rs b/csbindgen/src/parser.rs
index 163d46f..ca7e67f 100644
--- a/csbindgen/src/parser.rs
+++ b/csbindgen/src/parser.rs
@@ -1,8 +1,6 @@
 use crate::{builder::BindgenOptions, type_meta::*};
-use std::{
-    collections::{HashMap, HashSet},
-};
-use syn::{ForeignItem, Item, Pat, ReturnType};
+use std::collections::{HashMap, HashSet};
+use syn::{ForeignItem,  Item, Pat, ReturnType};
 
 enum FnItem {
     ForeignItem(syn::ForeignItemFn),
@@ -120,8 +118,8 @@ pub fn collect_type_alias(ast: &syn::File) -> Vec<(String, RustType)> {
                         name,
                         RustType {
                             type_name: alias.to_string(),
-                            type_kind: TypeKind::Normal
-                        }
+                            type_kind: TypeKind::Normal,
+                        },
                     ));
                 }
             }
@@ -217,22 +215,46 @@ fn parse_type(t: &syn::Type) -> RustType {
             if let syn::Type::Path(path) = &*t.elem {
                 return RustType {
                     type_name: path.path.segments.last().unwrap().ident.to_string(),
-                    type_kind: TypeKind::Pointer(if has_const { PointerType::ConstPointer } else { PointerType::MutPointer })
+                    type_kind: TypeKind::Pointer(if has_const {
+                        PointerType::ConstPointer
+                    } else {
+                        PointerType::MutPointer
+                    }),
                 };
             } else if let syn::Type::Ptr(t) = &*t.elem {
                 if let syn::Type::Path(path) = &*t.elem {
                     return RustType {
                         type_name: path.path.segments.last().unwrap().ident.to_string(),
-                        type_kind: TypeKind::Pointer(if has_const { PointerType::ConstPointerPointer } else { PointerType::MutPointerPointer })
+                        type_kind: TypeKind::Pointer(if has_const {
+                            PointerType::ConstPointerPointer
+                        } else {
+                            PointerType::MutPointerPointer
+                        }),
                     };
                 }
-            } 
+            }
         }
         syn::Type::Path(t) => {
-             return RustType{
-                type_name:t.path.segments.last().unwrap().ident.to_string(),
-                type_kind: TypeKind::Normal
-             }
+            let last_segment = t.path.segments.last().unwrap();
+            if let syn::PathArguments::AngleBracketed(x) = &last_segment.arguments {
+                // generics, only supports Option<> for null function pointer
+                if last_segment.ident.to_string() == "Option" {
+                    if let Some(x) = x.args.first() {
+                        if let syn::GenericArgument::Type(t) = x {
+                            let rust_type = parse_type(t);
+                            return RustType {
+                                type_name: "Option".to_string(),
+                                type_kind: TypeKind::Option(Box::new(rust_type)),
+                            };
+                        }
+                    }
+                }
+            } else {
+                return RustType {
+                    type_name: last_segment.ident.to_string(),
+                    type_kind: TypeKind::Normal,
+                };
+            }
         }
         syn::Type::Array(t) => {
             let mut digits = "".to_string();
@@ -256,8 +278,29 @@ fn parse_type(t: &syn::Type) -> RustType {
                 };
             };
         }
-        syn::Type::BareFn(_) => {
-            //todo!();
+        syn::Type::BareFn(t) => {
+            let mut parameters = Vec::new();
+
+            for arg in t.inputs.iter() {
+                let rust_type = parse_type(&arg.ty);
+
+                let name = if let Some((ident, _)) = &arg.name {
+                    ident.to_string()
+                } else {
+                    "".to_string()
+                };
+                parameters.push(Parameter { name, rust_type });
+            }
+
+            let ret = match &t.output {
+                syn::ReturnType::Default => None,
+                syn::ReturnType::Type(_, t) => Some(Box::new(parse_type(&t))),
+            };
+
+            return RustType {
+                type_name: "extern \"C\" fn".to_string(),
+                type_kind: TypeKind::Function(parameters, ret),
+            };
         }
         _ => {}
     };
diff --git a/csbindgen/src/type_meta.rs b/csbindgen/src/type_meta.rs
index 32b13a0..9609e92 100644
--- a/csbindgen/src/type_meta.rs
+++ b/csbindgen/src/type_meta.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::{collections::HashMap};
 
 use crate::builder::BindgenOptions;
 
@@ -51,8 +51,9 @@ pub struct RustType {
 pub enum TypeKind {
     Normal,
     Pointer(PointerType),
-    FixedArray(String, Option<PointerType>),        // digits
-    Function(Vec<RustType>, Option<Box<RustType>>), // parameter, return
+    FixedArray(String, Option<PointerType>),         // digits
+    Function(Vec<Parameter>, Option<Box<RustType>>), // parameter, return
+    Option(Box<RustType>),
 }
 
 #[derive(Clone, Debug)]
@@ -71,7 +72,7 @@ pub struct RustStruct {
 }
 
 impl RustType {
-    pub fn to_string(&self, type_path: &str) -> String {
+    pub fn to_rust_string(&self, type_path: &str) -> String {
         let mut sb = String::new();
 
         fn emit_pointer(sb: &mut String, p: &PointerType) {
@@ -118,8 +119,25 @@ impl RustType {
                 sb.push_str(digits.as_str());
                 sb.push(']');
             }
-            Function(x, y) => {
-                todo!();
+            Function(parameters, return_type) => {
+                emit_type_name(&mut sb); // extern fn
+                sb.push('(');
+                let params = parameters
+                    .iter()
+                    .map(|x| format!("{}: {}", x.escape_name(), x.rust_type.to_rust_string(type_path)))
+                    .collect::<Vec<_>>()
+                    .join(", ");
+                sb.push_str(params.as_str());
+                sb.push(')');
+                if let Some(t) = return_type {
+                    sb.push_str(" -> ");
+                    sb.push_str(t.to_rust_string(type_path).as_str());
+                }
+            },
+            Option(inner) =>  {
+                sb.push_str("Option<");
+                sb.push_str(inner.to_rust_string(type_path).as_str());
+                sb.push('>');
             }
         };
 
@@ -180,7 +198,7 @@ impl RustType {
 
         let mut sb = String::new();
 
-        match self.type_kind {
+        match &self.type_kind {
             TypeKind::FixedArray(_, _) => {
                 sb.push_str("fixed ");
 
@@ -194,6 +212,27 @@ impl RustType {
 
                 sb.push_str(type_name.as_str());
             }
+            TypeKind::Function(parameters, return_type) => {
+                sb.push_str("delegate* unmanaged[Cdecl]");
+                sb.push('<');
+                for p in parameters {
+                    sb.push_str(&p.rust_type.to_csharp_string(options, alias_map));
+                    sb.push_str(", ");
+                }
+                match return_type {
+                    Some(x) => {
+                        sb.push_str(&x.to_csharp_string(options, alias_map));
+                    }
+                    None => {
+                        sb.push_str("void");
+                    }
+                };
+                sb.push('>');
+            },
+            TypeKind::Option(inner) =>{
+                // function pointer can not annotate ? so emit inner only
+                sb.push_str(inner.to_csharp_string(options, alias_map).as_str());
+            },
             _ => {
                 sb.push_str(convert_type_name(use_type.type_name.as_str(), options).as_str());
 
@@ -229,6 +268,6 @@ impl RustType {
 
 impl std::fmt::Display for RustType {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.to_string(""))
+        write!(f, "{}", self.to_rust_string(""))
     }
 }
diff --git a/dotnet-sandbox/Program.cs b/dotnet-sandbox/Program.cs
index 22d4c74..abd25e6 100644
--- a/dotnet-sandbox/Program.cs
+++ b/dotnet-sandbox/Program.cs
@@ -13,16 +13,24 @@ using System.Text;
 
 unsafe
 {
-    // LibRust.call_bindgen();
+    [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvCdecl) })]
+    static int Method(int x) => x * x;
+
+    var tako = LibRust.callback_test(&Method);
+
+    
+    var n = LibRust.nullable_callback_test(null);
+
+    Console.WriteLine(n);
 
 
-    var ctx = LibRust.create_counter_context();
-    LibRust.insert_counter_context(ctx, 10);
-    LibRust.insert_counter_context(ctx, 20);
-    LibRust.insert_counter_context(ctx, 20);
-    LibRust.insert_counter_context(ctx, 30);
-    LibRust.insert_counter_context(ctx, 99);
-    LibRust.delete_counter_context(ctx);
+    //var ctx = LibRust.create_counter_context();
+    //LibRust.insert_counter_context(ctx, 10);
+    //LibRust.insert_counter_context(ctx, 20);
+    //LibRust.insert_counter_context(ctx, 20);
+    //LibRust.insert_counter_context(ctx, 30);
+    //LibRust.insert_counter_context(ctx, 99);
+    //LibRust.delete_counter_context(ctx);
 
     //var cString = LibRust.alloc_c_string();
     //var u8String = LibRust.alloc_u8_string();
diff --git a/dotnet-sandbox/method_call.cs b/dotnet-sandbox/method_call.cs
index 1057f7e..89889ee 100644
--- a/dotnet-sandbox/method_call.cs
+++ b/dotnet-sandbox/method_call.cs
@@ -11,6 +11,18 @@ namespace CsBindgen
     {
         const string __DllName = "csbindgen_tests";
 
+        [DllImport(__DllName, EntryPoint = "callback_test", CallingConvention = CallingConvention.Cdecl)]
+        public static extern int callback_test(delegate* unmanaged[Cdecl]<int, int> cb);
+
+        [DllImport(__DllName, EntryPoint = "nullable_callback_test", CallingConvention = CallingConvention.Cdecl)]
+        public static extern int nullable_callback_test(delegate* unmanaged[Cdecl]<int, int> cb);
+
+        [DllImport(__DllName, EntryPoint = "callback_test2", CallingConvention = CallingConvention.Cdecl)]
+        public static extern delegate* unmanaged[Cdecl]<int, int> callback_test2();
+
+        [DllImport(__DllName, EntryPoint = "callback", CallingConvention = CallingConvention.Cdecl)]
+        public static extern int callback(int a);
+
         [DllImport(__DllName, EntryPoint = "nop", CallingConvention = CallingConvention.Cdecl)]
         public static extern void nop();