What about hash tables ?<br><br>  | Val_table of (value, value) Hashtbl.t<br><br>If you have caml closures in your values (not in Val_closure but in Val_primitive), it is maybe not appropriate to use the default hash function that would choke on them. You should rather define your own hashing function --but defining a mutually recursive `value` type and Hashtable.make application will be delicate -- or change your representation of primitives to avoid ocaml functions (by reifying them into a concrete datatype for example).<br>

<br><div class="gmail_quote">On Tue, Oct 18, 2011 at 1:12 AM, Diego Olivier Fernandez Pons <span dir="ltr">&lt;<a href="mailto:dofp.ocaml@gmail.com">dofp.ocaml@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">

     Caml-list,<div><br></div><div>I have to write an interpreter for a language that has arrays explicitly indexed by anything that can be sequential (list, range, set)</div><div><br></div><div>    {string} airports = {&quot;ATL&quot;, &quot;JFK&quot;};</div>


<div>    range index = 1 .. 2;</div><div>    tuple recordAirport { airport : string; id : int }</div><div>    {recordAirport} otherAiports = { &lt;&quot;ATL&quot;, 12345&gt;, &lt;&quot;JFK&quot;, 42&gt;};</div><div><br></div>


<div>    int myArray [airports][index] = [[1, 2], [3, 4]];</div><div>    string myArray2 [a in recordAirports][i in index] = (i &lt; <a href="http://a.id" target="_blank">a.id</a>) ? &quot;unknown&quot; : a.airport ;</div>

<div>    int mySliceOfArray [a in recordAirports]  = sum (i in index) myArray[a.airport][i];</div>
<div><br></div><div>Usually the trick in interpreter implementation is to transform everything back to &quot;one-dimensional&quot; objects</div><div>- simple types</div><div>- inductive constructions for lists</div><div>

- curried functions</div>
<div><br></div><div>For instance in the book &quot;Le langage Caml&quot; the return type of the eval function is</div><div><br></div><div><div>type value =</div><div>   | Val_number of int</div><div>   | Val_boolean of bool</div>


<div>   | Val_pair of value * value</div><div>   | Val_nil</div><div>   | Val_cons of value * value</div><div>   | Val_closure of closure</div><div>   | Val_primitive of value -&gt; value</div><div>and closure = { definition: (pattern * expression) list; mutable environnement: environnement }</div>


<div>and environnement == (string * value) list</div></div><div><br></div><div>I don&#39;t see however how I am going to represent a type Val_Array given that the indexes can be of arbitrary type and in arbitrary number.</div>


<div>I haven&#39;t found either how to transform the arrays into inductive types like lists to avoid the issue.</div><div><br></div><div>Any suggestions ?</div><div><br></div><font color="#888888"><div>        Diego Olivier</div>


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