feat: convert introduction.typ to README.md (#479)

* dev: supports some functions for README

* feat: convert introduction.typ to README.md

crates/typlite/src/library.rs

@@ -5,6 +5,10 @@ use value::*;
 pub fn library() -> Scopes<Value> {
     let mut scopes = Scopes::new();
     scopes.define("link", link as RawFunc);
+    scopes.define("kbd", kbd as RawFunc);
+    // todo: how to import this function correctly?
+    scopes.define("cross-link", cross_link as RawFunc);
+    scopes.define("md-alter", md_alter as RawFunc);
     scopes.define("image", image as RawFunc);
     scopes.define("figure", figure as RawFunc);
     scopes
@@ -42,3 +46,31 @@ pub fn figure(mut args: Args) -> Result<Value> {
         _ => Err("figure only accepts image as body".into()),
     }
 }
+
+/// Evaluate a `kbd` element.
+pub fn kbd(mut args: Args) -> Result<Value> {
+    let key = get_pos_named!(args, key: EcoString);
+
+    Ok(Value::Content(eco_format!("<kbd>{key}</kbd>")))
+}
+
+/// Evaluate a `cross-link`.
+pub fn cross_link(mut args: Args) -> Result<Value> {
+    let dest = get_pos_named!(args, dest: EcoString);
+    let body = get_pos_named!(args, body: Content);
+
+    let dest = std::path::Path::new(dest.as_str()).with_extension("html");
+
+    Ok(Value::Content(eco_format!(
+        "[{body}](https://myriad-dreamin.github.io/tinymist/{dest})",
+        dest = dest.to_string_lossy()
+    )))
+}
+
+/// Evaluate a markdown alteration.
+pub fn md_alter(mut args: Args) -> Result<Value> {
+    let _left = get_pos_named!(args, left: Content);
+    let right = get_pos_named!(args, right: LazyContent);
+
+    Ok(Value::Content(right.0))
+}

crates/typlite/src/value.rs

@@ -27,6 +27,14 @@ impl fmt::Display for Content {
     }
 }
 
+pub struct LazyContent(pub EcoString);
+
+impl fmt::Display for LazyContent {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
 pub struct Args<'a> {
     pub vm: &'a mut TypliteWorker,
     pub args: ast::Args<'a>,
@@ -154,3 +162,14 @@ impl<'a> Eval<'a> for Content {
         Ok(Self(vm.convert(node)?))
     }
 }
+
+impl<'a> Eval<'a> for LazyContent {
+    fn eval(node: &'a SyntaxNode, vm: &mut TypliteWorker) -> Result<Self> {
+        let node = match node.cast() {
+            Some(s @ ast::Closure { .. }) => s.body().to_untyped(),
+            None => node,
+        };
+
+        Ok(Self(vm.convert(node)?))
+    }
+}