diff --git a/example/src/main.rs b/example/src/main.rs
index a6c4804..bcc5507 100644
--- a/example/src/main.rs
+++ b/example/src/main.rs
@@ -35,6 +35,9 @@ pub struct Printer<T: 'static + Display>
     #[input]
     input: In<T>,
 
+    #[output]
+    output: Out<T>,
+
     n: usize,
 }
 
diff --git a/oxydsp-dsp/src/blocks/math/basic.rs b/oxydsp-dsp/src/blocks/math/basic.rs
index ede9223..17557f6 100644
--- a/oxydsp-dsp/src/blocks/math/basic.rs
+++ b/oxydsp-dsp/src/blocks/math/basic.rs
@@ -1,15 +1,18 @@
-use std::ops::{Add, Mul};
+use std::ops::Add;
+use std::ops::Mul;
 
-use oxydsp_flowgraph::{
-    BlockIO,
-    block::{Block, BlockResult, SyncBlock},
-    io::{In, Out, PopIterable},
-    sync_block,
-    tag::TagMergable,
-};
+use oxydsp_flowgraph::BlockIO;
+use oxydsp_flowgraph::block::Block;
+use oxydsp_flowgraph::block::BlockResult;
+use oxydsp_flowgraph::block::SyncBlock;
+use oxydsp_flowgraph::io::In;
+use oxydsp_flowgraph::io::Out;
+use oxydsp_flowgraph::io::PopIterable;
+use oxydsp_flowgraph::sync_block;
+use oxydsp_flowgraph::tag::TagMergable;
 
 #[derive(BlockIO)]
-#[sync_block]
+#[sync_block(tagged)]
 pub struct Adder<Ia, Ib, O>
 where
     Ia: Add<Ib, Output = O> + 'static,
diff --git a/oxydsp-dsp/src/blocks/utilities/adapters.rs b/oxydsp-dsp/src/blocks/utilities/adapters.rs
index 930b218..1a17f42 100644
--- a/oxydsp-dsp/src/blocks/utilities/adapters.rs
+++ b/oxydsp-dsp/src/blocks/utilities/adapters.rs
@@ -1,9 +1,11 @@
-use oxydsp_flowgraph::{
-    BlockIO,
-    block::{Block, BlockResult},
-    io::{In, Out, PopIterable, stream},
-    tag::Tag,
-};
+use oxydsp_flowgraph::BlockIO;
+use oxydsp_flowgraph::block::Block;
+use oxydsp_flowgraph::block::BlockResult;
+use oxydsp_flowgraph::io::In;
+use oxydsp_flowgraph::io::Out;
+use oxydsp_flowgraph::io::PopIterable;
+use oxydsp_flowgraph::io::stream;
+use oxydsp_flowgraph::tag::Tag;
 
 #[derive(BlockIO)]
 pub struct Map<I: 'static, O: 'static, F>
@@ -84,12 +86,12 @@ impl<T: Clone + 'static> Block for Repeat<T>
         {
             if self.remaining == 0 || self.current.is_none()
             {
-                self.current = Some(reader.pop_tagged().unwrap());
+                self.current = Some(reader.pop().unwrap().into());
                 self.remaining = self.repetitions;
             }
 
             writer
-                .push(self.current.clone().unwrap())
+                .push(self.current.clone().unwrap().into())
                 .unwrap_or_else(|_| panic!());
 
             match &mut self.current
diff --git a/oxydsp-dsp/src/blocks/utilities/channels.rs b/oxydsp-dsp/src/blocks/utilities/channels.rs
index 67db127..369b29e 100644
--- a/oxydsp-dsp/src/blocks/utilities/channels.rs
+++ b/oxydsp-dsp/src/blocks/utilities/channels.rs
@@ -1,10 +1,14 @@
-use std::sync::mpsc::{Receiver, Sender, SyncSender};
+use std::sync::mpsc::Receiver;
+use std::sync::mpsc::Sender;
+use std::sync::mpsc::SyncSender;
 
-use oxydsp_flowgraph::{
-    BlockIO,
-    block::{Block, BlockResult},
-    io::{In, Out, PopIterable, stream},
-};
+use oxydsp_flowgraph::BlockIO;
+use oxydsp_flowgraph::block::Block;
+use oxydsp_flowgraph::block::BlockResult;
+use oxydsp_flowgraph::io::In;
+use oxydsp_flowgraph::io::Out;
+use oxydsp_flowgraph::io::PopIterable;
+use oxydsp_flowgraph::io::stream;
 
 #[derive(BlockIO)]
 pub struct RxSource<Rx, I: 'static>
diff --git a/oxydsp-flowgraph/oxydsp-flowgraph-macros/src/sync.rs b/oxydsp-flowgraph/oxydsp-flowgraph-macros/src/sync.rs
index 21e0a7d..abfedbd 100644
--- a/oxydsp-flowgraph/oxydsp-flowgraph-macros/src/sync.rs
+++ b/oxydsp-flowgraph/oxydsp-flowgraph-macros/src/sync.rs
@@ -5,7 +5,6 @@ use zyn::ast::at;
 use zyn::ext::AttrExt;
 use zyn::ext::FieldsExt;
 use zyn::ext::TypeExt;
-use zyn::quote;
 use zyn::quote::quote;
 use zyn::syn::Field;
 use zyn::syn::GenericParam;
@@ -217,9 +216,18 @@ fn sync_block_impl_block(item: zyn::syn::ItemStruct) -> zyn::TokenStream
                 @for (out_field in output_fields.iter())
                 {
                     let {{ out_field.ident.clone().unwrap() | ident: "{}_writer"}} = self.{{ out_field.ident }}.write();
-                    max_len = max_len.min({{ out_field.ident.clone().unwrap() | ident: "{}_writer"}}.len());
                 }
 
+                // Compute max_len
+                let max_len = [
+                    usize::MAX,
+                    @for (out_field in output_fields.iter())
+                    {
+                        {{ out_field.ident.clone().unwrap() | ident: "{}_writer"}}.len(),
+                    }
+                ].iter().min().unwrap();
+
+
                 @if (!input_fields.is_empty())
                 {
                     @sync_block_block_impl_with_inputs(item = item.clone(), input_fields = input_fields.clone(), output_fields = output_fields.clone())
@@ -289,25 +297,22 @@ fn sync_block_block_impl_with_inputs(
             &mut self.{{ in_field.ident }},
         }
     ).pop_iter()
-    .zip(0..max_len)
+    .take(max_len)
     .for_each(
     // Deconstruct foreach arguments
     |
-    (
         (@for (in_field in input_fields.iter())
         {
-            ({{in_field.ident.clone().unwrap() | ident:"{}_element"}},
+            oxydsp_flowgraph::tag::Tagged({{in_field.ident.clone().unwrap() | ident:"{}_element"}},
              {{in_field.ident.clone().unwrap() | ident:"{}_tag_opt"}}),
-        }),
-        _ // Ignore index
-    )
+        })
     |
     {
         // Create output tag
-        let tag = oxydsp_flowgraph::tag::Tag::merge_tag_opts([
+        let common_tag = oxydsp_flowgraph::tag::Tag::merge_tag_opts([
             @for (in_field in input_fields.iter())
             {
-                 {{in_field.ident.clone().unwrap() | ident:"{}_tag_opt"}},
+                 {{in_field.ident.clone().unwrap() | ident:"{}_tag_opt"}}.clone(),
             }
         ]);
 
@@ -319,26 +324,26 @@ fn sync_block_block_impl_with_inputs(
         }
         @else if (output_fields.len() == 1)
         {
-            let {{output_fields[0].ident.clone().unwrap() | ident:"{}_element"}}
+            let oxydsp_flowgraph::tag::Tagged({{output_fields[0].ident.clone().unwrap() | ident:"{}_element"}}, {{output_fields[0].ident.clone().unwrap() | ident:"{}_tag_opt"}})
         }
         @else
         {
             let (@for (out_field in output_fields.iter())
              {
-                 {{out_field.ident.clone().unwrap() | ident:"{}_element"}},
+                 oxydsp_flowgraph::tag::Tagged({{out_field.ident.clone().unwrap() | ident:"{}_element"}}, {{out_field.ident.clone().unwrap() | ident:"{}_tag_opt"}}),
              }
             )
         }
             = <Self as oxydsp_flowgraph::block::SyncBlock>::sync_work(state,
                 @if (input_fields.len() == 1)
                 {
-                    {{input_fields[0].ident.clone().unwrap() | ident:"{}_element"}},
+                    oxydsp_flowgraph::tag::Tagged({{input_fields[0].ident.clone().unwrap() | ident:"{}_element"}}, {{input_fields[0].ident.clone().unwrap() | ident:"{}_tag_opt"}}.clone())
                 }
                 @else
                 {
                     (@for (in_field in input_fields.iter())
                      {
-                         {{in_field.ident.clone().unwrap() | ident:"{}_element"}},
+                        oxydsp_flowgraph::tag::Tagged({{in_field.ident.clone().unwrap() | ident:"{}_element"}}, {{in_field.ident.clone().unwrap() | ident:"{}_tag_opt"}}.clone()),
                      }
                     )
                 }
@@ -348,9 +353,9 @@ fn sync_block_block_impl_with_inputs(
         @for (out_field in output_fields.iter())
         {
             {{ out_field.ident.clone().unwrap() | ident: "{}_writer"}}.push(
-                (
+                oxydsp_flowgraph::tag::Tagged(
                     {{ out_field.ident.clone().unwrap() | ident: "{}_element"}},
-                    tag.clone()
+                    {{ out_field.ident.clone().unwrap() | ident: "{}_tag_opt"}}.merge(common_tag),
                 )
                 );
         }
diff --git a/oxydsp-flowgraph/src/io.rs b/oxydsp-flowgraph/src/io.rs
index cd2df74..3178470 100644
--- a/oxydsp-flowgraph/src/io.rs
+++ b/oxydsp-flowgraph/src/io.rs
@@ -144,7 +144,7 @@ impl<T: 'static> Out<T>
                 {
                     Some(tag) =>
                     {
-                        let _ = writer.push_tagged(elt.0, tag);
+                        let _ = writer.push(Tagged(elt.0, Some(tag)));
                     }
                     None =>
                     {
@@ -174,6 +174,11 @@ impl<T> InReader<'_, T>
         self.data_reader.len()
     }
 
+    pub fn is_empty(&self) -> bool
+    {
+        self.len() == 0
+    }
+
     pub fn pop(&self) -> Option<Tagged<T>>
     {
         let data = self.data_reader.pop_with_index();
@@ -208,7 +213,12 @@ impl<T> OutWriter<'_, T>
         self.data_writer.len().min(self.tag_writer.len())
     }
 
-    pub fn push(&self, data: Tagged<T>) -> Result<(), (T, Option<Tag>)>
+    pub fn is_empty(&self) -> bool
+    {
+        self.len() == 0
+    }
+
+    pub fn push(&self, data: Tagged<T>) -> Result<(), Tagged<T>>
     {
         let (data, tag) = data.into();
         match self.data_writer.push(data)
@@ -219,13 +229,13 @@ impl<T> OutWriter<'_, T>
                 Ok(())
             }
             Ok(_) => Ok(()),
-            Err(data) => Err((data, tag)),
+            Err(data) => Err((data, tag).into()),
         }
     }
 
     pub fn push_no_tag(&self, data: T) -> Result<(), T>
     {
-        self.data_writer.push(data.into())
+        self.data_writer.push(data)
     }
 }