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<p>Many thanks to all for your responses and suggestions.</p>
<p>To answer your question Richard, I don't actually need a cyclical
structure. As I mentioned, this is a simplification of a more
specific problem. I didn't want to describe all the specifics to
ask a question. I need to design a tree, a variant of a HAMT tree,
but which can be traversed in both directions, from the root to
leafs and from leafs to the root (independently, i.e. starting
from a reference to a leaf rather than recursively). Tuples that
reference each other is one solution but not the only one
fortunately, i.e. I can add ids to each node and use another data
structure to store the mapping id-node, then store the id of the
parent in the child.</p>
<p>Thank you for the pointer to the book.<br>
</p>
<p>GrzegorzJ<br>
</p>
<br>
<div class="moz-cite-prefix">On 18/09/2017 00:53, Richard A. O'Keefe
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:0bc4e2f2-b1df-b753-6b20-d1144768a89a@cs.otago.ac.nz">On
further reflection, I suppose I should ask: <br>
Why is it that you think you need cyclic structures? <br>
What do you actually want to *do* with them? <br>
<br>
As a matter of curiosity, have you read Okasaki's <br>
book on functional data structures? <br>
<br>
(Didn't someone convert Okasaki's Edison library <br>
to Erlang at some point? What happened to that?) <br>
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