tabula rasa

output/src/view.rs

@@ -0,0 +1,87 @@
+use crate::*;
+#[macro_export] macro_rules! view {
+    ($Output:ty: |$self:ident: $State:ty| $expr:expr; {
+        $($sym:literal => $body:expr),* $(,)?
+    }) => {
+        impl Content<$Output> for $State {
+            fn content (&$self) -> impl Render<$Output> { $expr }
+        }
+        impl<'a> ViewContext<'a, $Output> for $State {
+            fn get_content_sym (&'a $self, value: &Value<'a>) -> Option<RenderBox<'a, $Output>> {
+                if let Value::Sym(s) = value {
+                    match *s {
+                        $($sym => Some($body),)*
+                        _ => None
+                    }
+                } else {
+                    panic!("expected content, got: {value:?}")
+                }
+            }
+        }
+    }
+}
+
+// An ephemeral wrapper around view state and view description,
+// that is meant to be constructed and returned from [Content::content].
+pub struct View<'a, T>(pub &'a T, pub SourceIter<'a>);
+impl<'a, O: Output + 'a, T: ViewContext<'a, O>> Content<O> for View<'a, T> {
+    fn content (&self) -> impl Render<O> {
+        let iter = self.1.clone();
+        while let Some((Token { value, .. }, _)) = iter.next() {
+            if let Some(content) = self.0.get_content(&value) {
+                return Some(content)
+            }
+        }
+        return None
+    }
+}
+// Provides components to the view.
+pub trait ViewContext<'a, E: Output + 'a>: Send + Sync
+    + Context<bool>
+    + Context<usize>
+    + Context<E::Unit>
+{
+    fn get_content (&'a self, value: &Value<'a>) -> Option<RenderBox<'a, E>> {
+        match value {
+            Value::Sym(_) => self.get_content_sym(value),
+            Value::Exp(_, _) => self.get_content_exp(value),
+            _ => panic!("only :symbols and (expressions) accepted here")
+        }
+    }
+    fn get_content_sym (&'a self, value: &Value<'a>) -> Option<RenderBox<'a, E>>;
+    fn get_content_exp (&'a self, value: &Value<'a>) -> Option<RenderBox<'a, E>> {
+        try_delegate!(self, *value, When::<RenderBox<'a, E>>);
+        try_delegate!(self, *value, Either::<RenderBox<'a, E>, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Align::<RenderBox<'a, E>>);
+        try_delegate!(self, *value, Bsp::<RenderBox<'a, E>, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Fill::<RenderBox<'a, E>>);
+        try_delegate!(self, *value, Fixed::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Min::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Max::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Shrink::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Expand::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Push::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Pull::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Margin::<_, RenderBox<'a, E>>);
+        try_delegate!(self, *value, Padding::<_, RenderBox<'a, E>>);
+        None
+    }
+}
+#[macro_export] macro_rules! try_delegate {
+    ($s:ident, $atom:expr, $T:ty) => {
+        if let Some(value) = <$T>::try_from_atom($s, $atom) {
+            return Some(value.boxed())
+        }
+    }
+}
+#[macro_export] macro_rules! try_from_expr {
+    (<$l:lifetime, $E:ident>: $Struct:ty: |$state:ident, $iter:ident|$body:expr) => {
+        impl<$l, $E: Output + $l, T: ViewContext<$l, $E>> TryFromAtom<$l, T> for $Struct {
+            fn try_from_expr ($state: &$l T, $iter: TokenIter<'a>) -> Option<Self> {
+                let mut $iter = $iter.clone();
+                $body;
+                None
+            }
+        }
+    }
+}