[mercury-users] Indexing & operational semantics

[Richard A. O'Keefe]

	From owner-mercury-users at cs.mu.OZ.AU Wed Feb  2 18:34:49 2000
	Date: Wed, 2 Feb 2000 16:27:56 +1100
	From: Peter Schachte <schachte at cs.mu.OZ.AU>
	To: mercury-users at cs.mu.OZ.AU
	Subject: Re: [mercury-users] Indexing & operational semantics
	References: <200002012324.MAA11690 at hermes.otago.ac.nz> <20000202150530.B396 at cs.mu.oz.au> <20000202153607.A10089 at hg.cs.mu.oz.au>
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	In-Reply-To: <20000202153607.A10089 at hg.cs.mu.oz.au>; from Fergus Henderson on Wed, Feb 02, 2000 at 03:36:08PM +1100
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	On Wed, Feb 02, 2000 at 03:36:08PM +1100, Fergus Henderson wrote:
	> For that one, Richard O'Keefe's argument about disallowing
	> such expressions on the grounds that they are likely to be
	> confusing is stronger.
	
Peter Schachte wrote
	Perhaps, but it's still going to be a nuissance to have to split an
	existing clause into two separate clauses just because you want to
	introduce a precondition to a clause that uses parallel conjunction.
	I think it would be less draconian, and just clear, to require
	explicit parentheses.

But that is *precisely* what my proposal was!
Ada lets you use 'and' and 'and then' in the same expression,
but not as "adjacent" operators.  You can have
	(A and B) and then C		=>Mercury	(A, B) && C
or	A and (B and then C)		=>Mercury	A, (B && C)
The only thing that is disallowed is
	A and B and then C.		=>Mercury	A, B && C

	If you just want to forbid mixing && and & in a clause, you could do
	that after parsing.
	
But why would anyone want to forbid _that_?
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