diff --git a/crates/generate/src/funcs.rs b/crates/generate/src/funcs.rs
index f624e15146..e886308f86 100644
--- a/crates/generate/src/funcs.rs
+++ b/crates/generate/src/funcs.rs
@@ -8,39 +8,34 @@ use crate::names::Names;
 //
 pub fn define_func(names: &Names, func: &witx::InterfaceFunc) -> TokenStream {
     let ident = names.func(&func.name);
+    let coretype = func.core_type();
 
-    let arg_signature = |param: &witx::InterfaceFuncParam| -> TokenStream {
-        let name = names.func_param(&param.name);
-        match param.tref.type_().passed_by() {
-            witx::TypePassedBy::Value(atom) => {
-                let atom = names.atom_type(atom);
-                quote!(#name: #atom)
-            }
-            witx::TypePassedBy::Pointer => {
-                let atom = names.atom_type(witx::AtomType::I32);
-                quote!(#name: #atom)
-            }
-            witx::TypePassedBy::PointerLengthPair => {
-                let atom = names.atom_type(witx::AtomType::I32);
-                let len_name = names.func_len_param(&param.name);
-                quote!(#name: #atom, #len_name: #atom)
-            }
+    let params = coretype.args.iter().map(|arg| match arg.signifies {
+        witx::CoreParamSignifies::Value(atom) => {
+            let atom = names.atom_type(atom);
+            let name = names.func_param(&arg.param.name);
+            quote!(#name : #atom)
         }
-    };
+        witx::CoreParamSignifies::PointerTo => {
+            let atom = names.atom_type(witx::AtomType::I32);
+            let name = names.func_ptr_binding(&arg.param.name);
+            quote!(#name: #atom)
+        }
+        witx::CoreParamSignifies::LengthOf => {
+            let atom = names.atom_type(witx::AtomType::I32);
+            let name = names.func_len_binding(&arg.param.name);
+            quote!(#name: #atom)
+        }
+    });
 
-    let params = func
-        .params
-        .iter()
-        .chain(func.results.iter().skip(1))
-        .map(arg_signature);
     let abi_args = quote!(
             ctx: &mut WasiCtx, memory: ::memory::GuestMemory,
             #(#params),*
     );
-    let abi_ret = if let Some(first_result) = func.results.get(0) {
-        match first_result.tref.type_().passed_by() {
-            witx::TypePassedBy::Value(atom) => names.atom_type(atom),
-            _ => unreachable!("first result should always be passed by value"),
+    let abi_ret = if let Some(ret) = &coretype.ret {
+        match ret.signifies {
+            witx::CoreParamSignifies::Value(atom) => names.atom_type(atom),
+            _ => unreachable!("ret should always be passed by value"),
         }
     } else if func.noreturn {
         // Ideally we would return `quote!(!)` here, but, we'd have to change
@@ -52,21 +47,34 @@ pub fn define_func(names: &Names, func: &witx::InterfaceFunc) -> TokenStream {
         quote!(())
     };
 
-    let err_type = func
-        .results
-        .get(0)
-        .map(|res| names.type_ref(&res.tref))
-        .unwrap_or_else(|| abi_ret.clone());
-    let err_val = func
-        .results
-        .get(0)
+    let err_type = coretype.ret.map(|ret| ret.param.tref);
+    let err_val = err_type
+        .clone()
         .map(|_res| quote!(#abi_ret::from(e)))
         .unwrap_or_else(|| quote!(()));
 
+    let error_handling: TokenStream = {
+        if let Some(tref) = &err_type {
+            let abi_ret = match tref.type_().passed_by() {
+                witx::TypePassedBy::Value(atom) => names.atom_type(atom),
+                _ => unreachable!("err should always be passed by value"),
+            };
+            let err_typename = names.type_ref(&tref);
+            quote! {
+                let err: #err_typename = ::memory::GuestErrorType::from_error(e, ctx);
+                return #abi_ret::from(err);
+            }
+        } else {
+            quote! {
+                panic!("error: {:?}", e)
+            }
+        }
+    };
+
     let marshal_args = func
         .params
         .iter()
-        .map(|p| marshal_arg(names, p, func.results.get(0).map(|r| &r.tref)));
+        .map(|p| marshal_arg(names, p, error_handling.clone()));
     let trait_args = func
         .params
         .iter()
@@ -84,88 +92,93 @@ pub fn define_func(names: &Names, func: &witx::InterfaceFunc) -> TokenStream {
         (tuple.clone(), tuple)
     };
 
+    // Return value pointers need to be validated before the api call, then
+    // assigned to afterwards. marshal_result returns these two statements as a pair.
     let marshal_rets = func
         .results
         .iter()
         .skip(1)
-        .map(|_result| quote! { unimplemented!("convert result..."); });
+        .map(|result| marshal_result(names, result, error_handling.clone()));
+    let marshal_rets_pre = marshal_rets.clone().map(|(pre, _post)| pre);
+    let marshal_rets_post = marshal_rets.map(|(_pre, post)| post);
+
+    let success = if let Some(err_type) = err_type {
+        let err_typename = names.type_ref(&err_type);
+        quote! {
+            let success:#err_typename = ::memory::GuestErrorType::success();
+            #abi_ret::from(success)
+        }
+    } else {
+        quote!()
+    };
 
     quote!(pub fn #ident(#abi_args) -> #abi_ret {
         #(#marshal_args)*
+        #(#marshal_rets_pre)*
         let #trait_bindings  = match ctx.#ident(#(#trait_args),*) {
             Ok(#trait_bindings) => #trait_rets,
             Err(e) => { return #err_val; },
         };
-        #(#marshal_rets)*
-        let success:#err_type = ::memory::GuestErrorType::success();
-        #abi_ret::from(success)
+        #(#marshal_rets_post)*
+        #success
     })
 }
 
 fn marshal_arg(
     names: &Names,
     param: &witx::InterfaceFuncParam,
-    error_type: Option<&witx::TypeRef>,
+    error_handling: TokenStream,
 ) -> TokenStream {
     let tref = &param.tref;
     let interface_typename = names.type_ref(&tref);
-    let name = names.func_param(&param.name);
 
-    let error_handling: TokenStream = {
-        if let Some(tref) = error_type {
-            let abi_ret = match tref.type_().passed_by() {
-                witx::TypePassedBy::Value(atom) => names.atom_type(atom),
-                _ => unreachable!("err should always be passed by value"),
+    let try_into_conversion = {
+        let name = names.func_param(&param.name);
+        quote! {
+            use ::std::convert::TryInto;
+            let #name: #interface_typename = match #name.try_into() {
+                Ok(a) => a,
+                Err(e) => {
+                    #error_handling
+                }
             };
-            let err_typename = names.type_ref(&tref);
-            quote! {
-                let err: #err_typename = ::memory::GuestErrorType::from_error(e, ctx);
-                return #abi_ret::from(err);
-            }
-        } else {
-            quote! {
-                panic!("error: {:?}", e)
-            }
         }
     };
 
-    let try_into_conversion = quote! {
-        use ::std::convert::TryInto;
-        let #name: #interface_typename = match #name.try_into() {
-            Ok(a) => a,
-            Err(e) => {
-                #error_handling
-            }
-        };
-    };
-
     match &*tref.type_() {
         witx::Type::Enum(_e) => try_into_conversion,
         witx::Type::Builtin(b) => match b {
             witx::BuiltinType::U8 | witx::BuiltinType::U16 | witx::BuiltinType::Char8 => {
                 try_into_conversion
             }
-            witx::BuiltinType::S8 | witx::BuiltinType::S16 => quote! {
-                let #name: #interface_typename = match (#name as i32).try_into() {
-                    Ok(a) => a,
-                    Err(e) => {
-                        #error_handling
+            witx::BuiltinType::S8 | witx::BuiltinType::S16 => {
+                let name = names.func_param(&param.name);
+                quote! {
+                    let #name: #interface_typename = match (#name as i32).try_into() {
+                        Ok(a) => a,
+                        Err(e) => {
+                            #error_handling
+                        }
                     }
                 }
-            },
+            }
             witx::BuiltinType::U32
             | witx::BuiltinType::S32
             | witx::BuiltinType::U64
             | witx::BuiltinType::S64
             | witx::BuiltinType::USize
             | witx::BuiltinType::F32
-            | witx::BuiltinType::F64 => quote! {
-                let #name = #name as #interface_typename;
-            },
+            | witx::BuiltinType::F64 => {
+                let name = names.func_param(&param.name);
+                quote! {
+                    let #name = #name as #interface_typename;
+                }
+            }
             witx::BuiltinType::String => unimplemented!("string types unimplemented"),
         },
         witx::Type::Pointer(pointee) => {
             let pointee_type = names.type_ref(pointee);
+            let name = names.func_param(&param.name);
             quote! {
                 let #name = match memory.ptr_mut::<#pointee_type>(#name as u32) {
                     Ok(p) => p,
@@ -177,6 +190,7 @@ fn marshal_arg(
         }
         witx::Type::ConstPointer(pointee) => {
             let pointee_type = names.type_ref(pointee);
+            let name = names.func_param(&param.name);
             quote! {
                 let #name = match memory.ptr::<#pointee_type>(#name as u32) {
                     Ok(p) => p,
@@ -189,3 +203,52 @@ fn marshal_arg(
         _ => unimplemented!("argument type marshalling"),
     }
 }
+
+fn marshal_result(
+    names: &Names,
+    result: &witx::InterfaceFuncParam,
+    error_handling: TokenStream,
+) -> (TokenStream, TokenStream) {
+    let tref = &result.tref;
+
+    let write_val_to_ptr = {
+        let pointee_type = names.type_ref(tref);
+        // core type is given func_ptr_binding name.
+        let ptr_name = names.func_ptr_binding(&result.name);
+        let pre = quote! {
+            let #ptr_name = match memory.ptr_mut::<#pointee_type>(#ptr_name as u32) {
+                Ok(p) => p,
+                Err(e) => {
+                    #error_handling
+                }
+            };
+        };
+        // trait binding returns func_param name.
+        let val_name = names.func_param(&result.name);
+        let post = quote! {
+            use ::memory::GuestTypeCopy;
+            #pointee_type::write_val(#val_name, &#ptr_name);
+        };
+        (pre, post)
+    };
+
+    match &*tref.type_() {
+        witx::Type::Builtin(b) => match b {
+            witx::BuiltinType::U8
+            | witx::BuiltinType::S8
+            | witx::BuiltinType::U16
+            | witx::BuiltinType::S16
+            | witx::BuiltinType::U32
+            | witx::BuiltinType::S32
+            | witx::BuiltinType::U64
+            | witx::BuiltinType::S64
+            | witx::BuiltinType::F32
+            | witx::BuiltinType::F64
+            | witx::BuiltinType::USize
+            | witx::BuiltinType::Char8 => write_val_to_ptr,
+            witx::BuiltinType::String => unimplemented!("string types"),
+        },
+        witx::Type::Enum(_e) => write_val_to_ptr,
+        _ => unimplemented!("marshal result"),
+    }
+}
diff --git a/crates/generate/src/names.rs b/crates/generate/src/names.rs
index 6465e7f832..acbb3b00aa 100644
--- a/crates/generate/src/names.rs
+++ b/crates/generate/src/names.rs
@@ -88,8 +88,13 @@ impl Names {
         format_ident!("{}", id.as_str().to_snake_case())
     }
 
-    /// For when you need a {name}_len parameter for passing an array:
-    pub fn func_len_param(&self, id: &Id) -> Ident {
+    /// For when you need a {name}_ptr binding for passing a value by reference:
+    pub fn func_ptr_binding(&self, id: &Id) -> Ident {
+        format_ident!("{}_ptr", id.as_str().to_snake_case())
+    }
+
+    /// For when you need a {name}_len binding for passing an array:
+    pub fn func_len_binding(&self, id: &Id) -> Ident {
         format_ident!("{}_len", id.as_str().to_snake_case())
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index fd287a0f0c..cf36236e83 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -62,8 +62,12 @@ pub mod test {
             );
             Ok(())
         }
-    }
 
+        fn bat(&mut self, an_int: u32) -> Result<f32, types::Errno> {
+            println!("bat: {}", an_int);
+            Ok((an_int as f32) * 2.0)
+        }
+    }
     // Errno is used as a first return value in the functions above, therefore
     // it must implement GuestErrorType with type Context = WasiCtx.
     // The context type should let you do logging or debugging or whatever you need
diff --git a/test.witx b/test.witx
index 16964d8eea..422d99bd72 100644
--- a/test.witx
+++ b/test.witx
@@ -25,4 +25,8 @@
     (param $a_lamer_excuse (@witx const_pointer $excuse))
     (param $two_layers_of_excuses (@witx pointer (@witx const_pointer $excuse)))
     (result $error $errno))
+  (@interface func (export "bat")
+    (param $an_int u32)
+    (result $error $errno)
+    (result $doubled_it f32))
 )