pub fn is_simple(&self) -> bool {
        self.start.is_none()
            && self.end.is_none()
            && self.stride.is_none()
            && self.kind == IterKind::ScalarIter
    }
Returns true if this is a simple iterator.

An iterator is simple if it has no start/stride/end specified (i.e., it iterates over all
the input data) and kind `ScalarIter`.
weld/src/ast/ast.rs