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From: dik@cwi.nl (Dik T. Winter)
Newsgroups: comp.compilers
Subject: Re: Enumerated data types
Keywords: Algol68, design, Ada
Message-ID: <2019@charon.cwi.nl>
Date: 27 Aug 90 19:39:24 GMT
References: <1990Aug23.134826.2865@forwiss.uni-passau.de> <3621@goanna.cs.rmit.oz.au>
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: dik@cwi.nl (Dik T. Winter)
Organization: CWI, Amsterdam
Lines: 21
Approved: compilers@esegue.segue.boston.ma.us


In article <3621@goanna.cs.rmit.oz.au> ok@goanna.cs.rmit.OZ.AU (Richard A. O'Keefe) writes:
 > The thing which made overloading tricky in Algol 68 was that Algol 68
 > combined overloading with automatic coercions.  Ada doesn't go in for
 > automatic coercion.

That is incorrect.  Algol 68 allows overloading for operators only, and
coercions are not performed on operands of operators.  For instance in
the context of:
	'proc'('real','int')'real' + = ('real' r, 'int' i)'real': ....
the expression
	1.0 + 1.0
can still not be resolved, i.e. widening does not take place.  Similar
for other coercions.  The only kind of coercions allowed for operands
is 'dereferencing', but that is common to other languages (and implicitly
also in Ada).

Ada is much trickier because overloading not only depends on operand
types (as in Algol 68) but also on result type.
--
dik t. winter, cwi, amsterdam, nederland
dik@cwi.nl
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