Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucsd!hub!eiffel!bertrand
From: bertrand@eiffel.UUCP (Bertrand Meyer)
Newsgroups: comp.lang.eiffel
Subject: Re: Implies
Summary: implies is there
Message-ID: <202@eiffel.UUCP>
Date: 6 Oct 89 17:54:21 GMT
References: <1473@moondance.cs.uq.oz>
Organization: Interactive Software Engineering, Santa Barbara CA
Lines: 26

In article <1473@moondance.cs.uq.oz>, gjc@batserver.cs.uq.oz (G.J. Cumming)
suggests two new operators, implies and limplies, such that

    P implies  Q         means      not P or Q
    P limplies Q         means      not P or else Q

In fact, version 2.2 includes the implies operator, with the semantics
he suggests for limplies (or else). It was not felt necessary to include
two versions, and the most useful semantics seemed to be the non-strict
one (``non-strict'' operators being those such as `and then', `or else'
and the new `implies' which may yield a result even when one of their
operands is not defined).

As a minor syntactic comment, no Eiffel keyword is an abbreviation, so
that a different name would have had to be found for `limplies' had
two operators been retained.

> 		Maybe not a great change, but certainly makes reading an
> 		assertion a bit easier.

Indeed, `implies' has so far been used essentially in assertions, and many
assertions of the Data Structure Library have been made simpler through
its introduction.

-- Bertrand Meyer
bertrand@eiffel.com