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From: Martin Dowie <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.fortran,comp.lang.ada
Subject: Re: Shortcut logicals
Date: Tue, 1 Feb 2005 06:49:00 +0000 (UTC)
Organization: BT Openworld
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Date: 2005-02-01T06:49:00+00:00
List-Id: <comp.lang.ada>

Robert A Duff wrote:
> Sorry, I've no idea what the Fortran rules are.
> 
> In Ada, the above expression is syntactically illegal -- compile time
> error.  You can write:
> 
>     (cond1 and cond2) and then (cond3 and cond4)
> 
> or:
> 
>     ((cond1 and cond2) and then cond3) and cond4)
> 
> for example.
> 
> "and" is just a function call.  If you say "X and Y" then X and Y are
> both evaluated (in either order) and passed to the "and" function.  The
> predefined version of "and" returns True if both are True.  But "and
> then" is a short-circuit control form: if you say "X and then Y", X is
> evaluated first, and if it's True, you're done.  Otherwise (X is False)
> Y is evaluated.

Bob,

For clarity, I think you got the last bits a little wrong... If X is 
"True" then Y is evaluated otherwise (X is "False"), Y is not evaluated.

What you said would be right if it was an "or else" short-circuit form.

Cheers

-- Martin