Draft incremental `markdown` parsing

Specially useful when dealing with long Markdown
streams, like LLMs.

2 files changed, 86 insertions, 12 deletions

diff --git a/examples/markdown/Cargo.toml b/examples/markdown/Cargo.toml
index cb74b954..fa6ced74 100644
--- a/examples/markdown/Cargo.toml
+++ b/examples/markdown/Cargo.toml
@@ -7,6 +7,6 @@ publish = false
 
 [dependencies]
 iced.workspace = true
-iced.features = ["markdown", "highlighter", "debug"]
+iced.features = ["markdown", "highlighter", "tokio", "debug"]
 
 open = "5.3"
diff --git a/examples/markdown/src/main.rs b/examples/markdown/src/main.rs
index 5605478f..a55e91d2 100644
--- a/examples/markdown/src/main.rs
+++ b/examples/markdown/src/main.rs
@@ -1,23 +1,37 @@
 use iced::highlighter;
-use iced::widget::{self, markdown, row, scrollable, text_editor};
-use iced::{Element, Fill, Font, Task, Theme};
+use iced::time::{self, milliseconds};
+use iced::widget::{
+    self, hover, markdown, right, row, scrollable, text_editor, toggler,
+};
+use iced::{Element, Fill, Font, Subscription, Task, Theme};
 
 pub fn main() -> iced::Result {
     iced::application("Markdown - Iced", Markdown::update, Markdown::view)
+        .subscription(Markdown::subscription)
         .theme(Markdown::theme)
         .run_with(Markdown::new)
 }
 
 struct Markdown {
     content: text_editor::Content,
-    items: Vec<markdown::Item>,
+    mode: Mode,
     theme: Theme,
 }
 
+enum Mode {
+    Oneshot(Vec<markdown::Item>),
+    Stream {
+        pending: String,
+        parsed: markdown::Content,
+    },
+}
+
 #[derive(Debug, Clone)]
 enum Message {
     Edit(text_editor::Action),
     LinkClicked(markdown::Url),
+    ToggleStream(bool),
+    NextToken,
 }
 
 impl Markdown {
@@ -29,7 +43,7 @@ impl Markdown {
         (
             Self {
                 content: text_editor::Content::with_text(INITIAL_CONTENT),
-                items: markdown::parse(INITIAL_CONTENT).collect(),
+                mode: Mode::Oneshot(markdown::parse(INITIAL_CONTENT).collect()),
                 theme,
             },
             widget::focus_next(),
@@ -44,13 +58,48 @@ impl Markdown {
                 self.content.perform(action);
 
                 if is_edit {
-                    self.items =
-                        markdown::parse(&self.content.text()).collect();
+                    self.mode = match self.mode {
+                        Mode::Oneshot(_) => Mode::Oneshot(
+                            markdown::parse(&self.content.text()).collect(),
+                        ),
+                        Mode::Stream { .. } => Mode::Stream {
+                            pending: self.content.text(),
+                            parsed: markdown::Content::parse(""),
+                        },
+                    }
                 }
             }
             Message::LinkClicked(link) => {
                 let _ = open::that_in_background(link.to_string());
             }
+            Message::ToggleStream(enable_stream) => {
+                self.mode = if enable_stream {
+                    Mode::Stream {
+                        pending: self.content.text(),
+                        parsed: markdown::Content::parse(""),
+                    }
+                } else {
+                    Mode::Oneshot(
+                        markdown::parse(&self.content.text()).collect(),
+                    )
+                };
+            }
+            Message::NextToken => match &mut self.mode {
+                Mode::Oneshot(_) => {}
+                Mode::Stream { pending, parsed } => {
+                    if pending.is_empty() {
+                        self.mode = Mode::Oneshot(parsed.items().to_vec());
+                    } else {
+                        let mut tokens = pending.split(' ');
+
+                        if let Some(token) = tokens.next() {
+                            parsed.push_str(&format!("{token} "));
+                        }
+
+                        *pending = tokens.collect::<Vec<_>>().join(" ");
+                    }
+                }
+            },
         }
     }
 
@@ -63,20 +112,45 @@ impl Markdown {
             .font(Font::MONOSPACE)
             .highlight("markdown", highlighter::Theme::Base16Ocean);
 
+        let items = match &self.mode {
+            Mode::Oneshot(items) => items.as_slice(),
+            Mode::Stream { parsed, .. } => parsed.items(),
+        };
+
         let preview = markdown(
-            &self.items,
+            items,
             markdown::Settings::default(),
             markdown::Style::from_palette(self.theme.palette()),
         )
         .map(Message::LinkClicked);
 
-        row![editor, scrollable(preview).spacing(10).height(Fill)]
-            .spacing(10)
-            .padding(10)
-            .into()
+        row![
+            editor,
+            hover(
+                scrollable(preview).spacing(10).width(Fill).height(Fill),
+                right(
+                    toggler(matches!(self.mode, Mode::Stream { .. }))
+                        .label("Stream")
+                        .on_toggle(Message::ToggleStream)
+                )
+                .padding([0, 20])
+            )
+        ]
+        .spacing(10)
+        .padding(10)
+        .into()
     }
 
     fn theme(&self) -> Theme {
         self.theme.clone()
     }
+
+    fn subscription(&self) -> Subscription<Message> {
+        match self.mode {
+            Mode::Oneshot(_) => Subscription::none(),
+            Mode::Stream { .. } => {
+                time::every(milliseconds(20)).map(|_| Message::NextToken)
+            }
+        }
+    }
 }