Add Value type and replace dyn-nodes with call-exprs 🏗

- In addition to syntax trees there are now `Value`s, which syntax trees can be evaluated into (e.g. the tree is `5+5` and the value is `10`)
- Parsing is completely pure, function calls are not parsed into nodes, but into simple call expressions, which are resolved later
- Functions aren't dynamic nodes anymore, but simply functions which receive their arguments as a table and the layouting context
- Functions may return any `Value`
- Layouting is powered by functions which return the new `Commands` value, which informs the layouting engine what to do
- When a function returns a non-`Commands` value, the layouter simply dumps the value into the document in monospace

1 files changed, 3 insertions, 5 deletions

diff --git a/src/syntax/span.rs b/src/syntax/span.rs
index 923d13c2..89f773c7 100644
--- a/src/syntax/span.rs
+++ b/src/syntax/span.rs
@@ -39,13 +39,11 @@ impl<T> Offset for SpanVec<T> {
 }
 
 /// A value with the span it corresponds to in the source code.
-#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 #[cfg_attr(feature = "serialize", derive(Serialize))]
 pub struct Spanned<T> {
-    /// The value.
-    pub v: T,
-    /// The corresponding span.
     pub span: Span,
+    pub v: T,
 }
 
 impl<T> Spanned<T> {
@@ -99,7 +97,7 @@ impl<T: Debug> Debug for Spanned<T> {
 }
 
 /// Locates a slice of source code.
-#[derive(Copy, Clone, Hash)]
+#[derive(Copy, Clone, Ord, PartialOrd, Hash)]
 #[cfg_attr(feature = "serialize", derive(Serialize))]
 pub struct Span {
     /// The inclusive start position.