Add documentation for Dispatcher, Chain, and Renderer

1 files changed, 71 insertions, 0 deletions

diff --git a/docs/pages/2-basic/5-renderer.md b/docs/pages/2-basic/5-renderer.md
index f3e09de..1f566f2 100644
--- a/docs/pages/2-basic/5-renderer.md
+++ b/docs/pages/2-basic/5-renderer.md
@@ -4,3 +4,74 @@
 </p>
 
 ---
+
+## Intro
+
+`Renderer` is similar to [Chain](pages/2-basic/4-chain) in that they both handle processing for a specific type. The difference is: [Chain](pages/2-basic/4-chain) transforms the type, while `Renderer` terminates the program and prints the information of that type to the terminal.
+
+A type can be processed by both [Chain](pages/2-basic/4-chain) and `Renderer`. If the type is `route_chain`ed, the system will search for a [Chain](pages/2-basic/4-chain) capable of handling that type. If none is found, it will automatically be routed to the `Renderer` to print the result of that type.
+
+The following example demonstrates how to handle rendering logic:
+
+```rust
+dispatcher!("hello",
+    HelloCommand => HelloEntry);
+
+pack!(ParsedHello = String);
+
+// It's the Chain defined in the Dispatcher chapter
+#[chain]
+async fn parse_hello(prev: HelloEntry) -> NextProcess {
+    let args = &*prev;
+    let first = args
+        .first()
+        .cloned()
+        .unwrap_or_else(|| 
+            "World".to_string()
+        );
+
+    // Distribute the type to the Renderer
+    ParsedHello::new(first).to_render()
+}
+
+// Define the renderer to 
+//   handle rendering of ParsedHello
+#[renderer]
+fn render_hello(prev: ParsedHello) {
+    // Use r_println or r_print to 
+    //   render the content of ParsedHello
+    r_println!("Hello, {}!", *prev)
+}
+```
+
+> **About r_print**
+>
+> `r_print!` can only be used inside a `Renderer`. This is because after the `renderer!` macro expands, it injects `r: &mut RenderResult` into the context.
+>
+> And `r_print!` directly writes content to the value `r`.
+> This means: if there is no `&mut RenderResult` named `r` in the context, `r_print!` cannot be used.
+
+## Manual Impl
+
+> ⚠️ WARNING
+>
+> The following content is not yet fully implemented; currently, only the `renderer!` macro is allowed for implementation.
+
+Similarly, you can also manually implement `Renderer`,
+
+but note that inside the `renderer!` macro, a `register_type!` macro is executed. This macro itself does not expand into any content; it is only used to inform the `gen_program` context that the type exists:
+
+```rust
+struct RenderHello;
+impl Renderer for RenderHello {
+    type Previous = ParsedHello;
+    fn render(
+        prev: Self::Previous, 
+        r: &mut RenderResult
+    ) {
+        r_println!("Hello, {}!", *prev)
+    }
+}
+ 
+register_type!(ParsedHello);
+```