Why no immutable double linked list in Scala collections?

Question

Looking at this question, where the questioner is interested in the first and last instances of some element in a List, it seems a more efficient solution would be

Answer 1

As a supplemental to the answer of @KimStebel I like to add:
If you are searching for a data structure suitable for the question that motivated you to ask this question, then you might have a look at Extreme Cleverness: Functional Data Structures in Scala by @DanielSpiewak.