proc, view: fix usage of builtins

output/src/ops/either.rs

@@ -0,0 +1,38 @@
+use crate::*;
+
+/// Show one item if a condition is true and another if the condition is false
+pub struct Either<A, B>(pub bool, pub A, pub B);
+impl<A, B> Either<A, B> {
+    /// Create a ternary condition.
+    pub const fn new (c: bool, a: A, b: B) -> Self {
+        Self(c, a, b)
+    }
+}
+#[cfg(feature = "dsl")]
+impl<A, B, T: Dsl<bool> + Dsl<A> + Dsl<B>> Namespace<T> for Either<A, B> {
+    fn take_from <'source> (
+        state: &T,
+        token: &mut TokenIter<'source>
+    ) -> Perhaps<Self> {
+        if let Some(Token { value: Value::Key("either"), .. }) = token.peek() {
+            let base = token.clone();
+            let _ = token.next().unwrap();
+            return Ok(Some(Self(
+                state.take_or_fail(token, "either: no condition")?,
+                state.take_or_fail(token, "either: no content 1")?,
+                state.take_or_fail(token, "either: no content 2")?,
+            )))
+        }
+        Ok(None)
+    }
+}
+impl<E: Output, A: Render<E>, B: Render<E>> Content<E> for Either<A, B> {
+    fn layout (&self, to: E::Area) -> E::Area {
+        let Self(cond, a, b) = self;
+        if *cond { a.layout(to) } else { b.layout(to) }
+    }
+    fn render (&self, to: &mut E) {
+        let Self(cond, a, b) = self;
+        if *cond { a.render(to) } else { b.render(to) }
+    }
+}