feat: bidi for containers

crates/erg_common/traits.rs

@@ -1267,3 +1267,26 @@ pub trait StructuralEq {
 pub trait __Str__ {
     fn __str__(&self) -> String;
 }
+
+pub trait OptionalTranspose {
+    type Output;
+    type Fill;
+    /// `self: Option<_>`
+    fn transpose(self, fill: Self::Fill) -> Self::Output
+    where
+        Self: Sized;
+}
+
+impl<T: Clone> OptionalTranspose for Option<Vec<T>> {
+    type Output = Vec<Option<T>>;
+    type Fill = usize;
+    fn transpose(self, fill: Self::Fill) -> Self::Output
+    where
+        Self: Sized,
+    {
+        match self {
+            Some(v) => v.into_iter().map(Some).collect(),
+            None => vec![None; fill],
+        }
+    }
+}