Interesting. I&#x27;ve never heard of D-list nomenclature before.<p>With the A-list method you typically need to write a &quot;zipper&quot; function, that recursively conses the heads of two lists to generate the A-list. Makes &quot;apply&quot; an expensive operation with needless allocations.<p>What&#x27;s great about D-lists is that the &quot;make-env&quot; method is just a single cons operation. Clearly superior. I&#x27;m surprised its not more well known.