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From: fjh@mundook.cs.mu.OZ.AU (Fergus Henderson)
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/04/28
Message-ID: <5k2081$oms@mulga.cs.mu.OZ.AU>#1/1
X-Deja-AN: 237889781
References: <01bc4e9b$ac0e7fa0$72041dc2@lightning>
 <335F5971.6375@elca-matrix.ch> <E95y9L.AK1@world.std.com>
 <dewar.861930356@merv> <E973qr.89t@world.std.com> <dewar.862141915@merv>
 <5jvlt7$54b@mulga.cs.mu.OZ.AU> <dewar.862152677@merv>
Organization: Comp Sci, University of Melbourne
Newsgroups: comp.lang.ada
Date: 1997-04-28T00:00:00+00:00
List-Id: <comp.lang.ada>


dewar@merv.cs.nyu.edu (Robert Dewar) writes:

>Fergus said
>
><<The Mercury language includes support for the equivalent of
>string case statements [...]
>I leave it to the reader to judge what conclusions should be
>drawn from this data.>>
>
>Interesting: I really can't see any utility in this feature in a compiler
>so it is a surprise to me that it is used in any compiler ... Usually
>you want to do all string recognizion in the context of a general names
>table that includes user defined words as well as system words. Fergus
>can you give a hint of typical example of how this is used.

In examples in the Mercury compiler, the strings involved are
	- the names of operators
	- the names of procedures for which the compiler generates inline code
	- names to special-case when doing name mangling
	...

Some examples I see use Mercury predicates as small in-memory read-only
relational databases; for example:

	% areas in 1000s of square miles
	:- pred area(string, int).
	:- mode area(in, out).
	area("china",           3380).
	area("india",           1139).
	area("ussr",            8708).
	area("usa",             3609).
	area("indonesia",        570).
	area("japan",            148).
	...

I suppose in Ada you could handle these sorts of examples
by declaring a constant array of records, making sure that the array
was sorted, and using binary search.

--
Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3         |     -- the last words of T. S. Garp.