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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Discriminated records are not the most efficient, but ...
Date: Mon, 23 Aug 2010 07:43:26 +0200
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Date: 2010-08-23T07:43:26+02:00
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* Yannick Duchêne (Hibou57):

> In ML : a functor has the following signature: “structure ->
> structure”. So at first sight, this may seems ML functors cannot model
> Ada packages.  But as a functor takes a structure to return a
> structure, this is exactly  the same as with an Ada generic
> instantiation. As in ML a functor cannot  create a structure signature
> and can only create a structure matching a  structure signature,
> finally, application of an ML functor exactly match  the process of
> instantiating an Ada generic.

Except that ML favors structural typing, and Ada is focused strongly
on nominal typing.

> Conclusion: the Ada package system can be properly modeled with ML.

Standard ML doesn't support functors nested in structures and
higher-order functors, but both are a common extension.

>    Definition of an ML signature = Ada specification of a package or
> generic package (formal part excluded)

No, these two aren't equivalent.  You cannot apply a specification to
a package to get a new package (with a restricted interface, as some
sort of type conversion).  In Standard ML, you can.