Implement type-of builtin function

src/builtin/meta.rs

@@ -44,4 +44,8 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
         };
         Some(Value::Ident(unit, QuoteKind::Double))
     });
+    decl!(f "type-of", |args| {
+        let value = arg!(args, 0, "value");
+        Some(Value::Ident(value.kind().to_owned(), QuoteKind::None))
+    });
 }

src/value.rs

@@ -197,11 +197,7 @@ impl Display for Value {
                     .join(sep.as_str())
             ),
             Self::Color(c) => write!(f, "{}", c),
-            Self::BinaryOp(lhs, op, rhs) => match op {
-                Op::Plus => write!(f, "{}", *lhs.clone() + *rhs.clone()),
-                Op::Minus => write!(f, "{}", *lhs.clone() - *rhs.clone()),
-                _ => write!(f, "{}{}{}", lhs, op, rhs),
-            },
+            Self::BinaryOp(..) => write!(f, "{}", self.eval()),
             Self::Paren(val) => write!(f, "{}", val),
             Self::Ident(val, kind) => write!(f, "{}{}{}", kind.as_str(), val, kind.as_str()),
             Self::True => write!(f, "true"),
@@ -227,6 +223,32 @@ impl Value {
         }
     }
 
+    pub fn kind(&self) -> &'static str {
+        match self {
+            Value::Color(..) => "color",
+            Value::Ident(..) => "string",
+            Value::Dimension(..) => "number",
+            Value::List(..) => "list",
+            // Value::Function(..) => "function",
+            Value::True | Value::False => "bool",
+            Value::Null => "null",
+            Value::BinaryOp(..) => self.eval().kind(),
+            _ => "unknown",
+
+        }
+    }
+
+    pub fn eval(&self) -> Self {
+        match self {
+            Self::BinaryOp(lhs, op, rhs) => match op {
+                Op::Plus => *lhs.clone() + *rhs.clone(),
+                Op::Minus => *lhs.clone() - *rhs.clone(),
+                _ => Self::BinaryOp(lhs.clone(), op.clone(), rhs.clone()),
+            }
+            _ => self.clone(),
+        }
+    }
+
     pub fn from_tokens<I: Iterator<Item = Token>>(
         toks: &mut Peekable<I>,
         scope: &Scope,

tests/meta.rs

@@ -58,3 +58,68 @@ test!(
     "a {\n  color: unit($number: 1px)\n}\n",
     "a {\n  color: \"px\";\n}\n"
 );
+test!(
+    type_of_number,
+    "a {\n  color: type-of(1)\n}\n",
+    "a {\n  color: number;\n}\n"
+);
+test!(
+    type_of_number_unit,
+    "a {\n  color: type-of(1px)\n}\n",
+    "a {\n  color: number;\n}\n"
+);
+test!(
+    type_of_unquoted,
+    "a {\n  color: type-of(foo)\n}\n",
+    "a {\n  color: string;\n}\n"
+);
+test!(
+    type_of_sgl_unquoted,
+    "a {\n  color: type-of('red')\n}\n",
+    "a {\n  color: string;\n}\n"
+);
+test!(
+    type_of_dbl_unquoted,
+    "a {\n  color: type-of(\"red\")\n}\n",
+    "a {\n  color: string;\n}\n"
+);
+// test!(
+//     type_of_3_hex_color,
+//     "a {\n  color: type-of(#fff)\n}\n",
+//     "a {\n  color: color;\n}\n"
+// );
+// test!(
+//     type_of_6_hex_color,
+//     "a {\n  color: type-of(#ffffff)\n}\n",
+//     "a {\n  color: color;\n}\n"
+// );
+// test!(
+//     type_of_named_color,
+//     "a {\n  color: type-of(red)\n}\n",
+//     "a {\n  color: color;\n}\n"
+// );
+// test!(
+//     type_of_spaced_list,
+//     "a {\n  color: type-of(1 2 3)\n}\n",
+//     "a {\n  color: list;\n}\n"
+// );
+test!(
+    type_of_true,
+    "a {\n  color: type-of(true)\n}\n",
+    "a {\n  color: bool;\n}\n"
+);
+test!(
+    type_of_false,
+    "a {\n  color: type-of(false)\n}\n",
+    "a {\n  color: bool;\n}\n"
+);
+test!(
+    type_of_null,
+    "a {\n  color: type-of(null)\n}\n",
+    "a {\n  color: null;\n}\n"
+);
+test!(
+    type_of_ident_plus_ident,
+    "a {\n  color: type-of(hi + bye)\n}\n",
+    "a {\n  color: string;\n}\n"
+);