[plt-scheme] How to insert an element in empty list?

From: Jakub Piotr Cłapa (jpc at pld-linux.org)
Date: Mon Aug 13 05:20:20 EDT 2007

jerzy.karczmarczuk at info.unicaen.fr wrote:
> Bill Wood writes:
>> A fairly common technique is to use a so-called "headed list",
>> consisting of a list with a dummy first element.  The list is "empty"
>> when the tail of the headed list is empty, you add to the front by
>> inserting a fresh cons containing the new item between the head and the
>> first "real" member (or nil if it is "empty"), etc.  This way you need
>> not treat the empty structure as a special case so code is simplified.
> This is a trick which may or may not be useful. Still, the empty structure
> IS a different animal, and "simplifying" the code in such a manner -
> 1. Introduces an overhead.
> 2. May make the code less readable, more error prone...

Maybe a box would do? 
You could then just cons new elements and replace the box contents with 
the new list.

Jakub Piotr Cłapa

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