test: add get_color (bulky!)

src/eval.rs

@@ -192,8 +192,9 @@ pub fn eval_view <'a, O: Screen + 'a, S> (
 /// #[namespace(bool)]
 /// #[namespace(u8)]
 /// #[namespace(u16)]
-/// #[namespace(Color try_to_color)]
+/// #[namespace(Color get_color)]
 /// struct State;
+///
 /// impl Interpret<Tui, Option<XYWH<u16>>> for State {
 ///     fn interpret_expr <'a> (&'a self, _: &mut Tui, lang: &'a impl Expression)
 ///         -> Usually<Option<XYWH<u16>>>
@@ -202,6 +203,36 @@ pub fn eval_view <'a, O: Screen + 'a, S> (
 ///     }
 /// }
 ///
+/// fn get_color (state: &State, src: impl Language) -> Perhaps<Color> {
+///     if let Some(expr) = src.expr()? {
+///         match (expr.head()?, expr.tail()?) {
+///             (Some("g"),   Some(tail)) => {
+///                 let n: u8 = state.namespace(tail.head().map_err(Into::into))?.ok_or(LanguageError::Domain("not gray"))?;
+///                 Ok(Some(Color::Rgb(n, n, n)))
+///             },
+///             (Some("rgb"), Some(tail)) => {
+///                 let r: u8 = state.namespace(tail.head().map_err(Into::into))?
+///                     .ok_or(LanguageError::Domain("not red"))?;
+///                 let g: u8 = state.namespace(tail.tail().head().map_err(Into::into))?
+///                     .ok_or(LanguageError::Domain("not green"))?;
+///                 let b: u8 = state.namespace(tail.tail().tail().head().map_err(Into::into))?
+///                     .ok_or(LanguageError::Domain("not blue"))?;
+///                 Ok(Some(Color::Rgb(r, g, b)))
+///             },
+///             (Some(_),     _) => return Err(format!("not a color expression: {expr}").into()),
+///             (None,        _) => return Err(format!("not a color expression: {expr}").into()),
+///         }
+///     } else if let Ok(Some(sym)) = src.word() {
+///         Ok(match sym {
+///             ":color/bg" => Some(Color::Rgb(28, 32, 36)),
+///             ":color/fg" => Some(Color::Rgb(98, 92, 96)),
+///             _ => return Err(format!("not a color: {sym}").into())
+///         })
+///     } else {
+///         return Err(format!("not a color: {:?}", src.src()?).into())
+///     }
+/// }
+///
 /// # fn main () -> tengri::Usually<()> {
 /// let state = State;
 /// let mut out = Tui::new(80, 25);