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From: andru@rhialto.sgi.com (Andrew Myers)
Newsgroups: comp.lang.pascal
Subject: Re: Standard Pascal
Message-ID: <203@odin.SGI.COM>
Date: 12 Jul 89 18:28:07 GMT
References: <8736@pyr.gatech.EDU>
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Distribution: usa
Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <8736@pyr.gatech.EDU> gus@pyr.gatech.EDU (gus Baird) writes:
>
>>
>>             I don't see how this differs at all from
>>
>>	repeat
>>	  read( input, ch);
>>	until not (ch in [space, tab, newline, cr, formfeed]);
>
>No! There's a TREMENDOUS difference between
>                                                     
>    repeat 
>	read(FileVar,ch)
>    until ch {is whatever};
>                                                     
>and
>                                                     
>    while FileVar^ {is not whatever} do
>	get(input);
>                                                     
>far beyond the trivial savings of a local variable.
>                                                   
>The point is that that the version with read consumes the character 
>that stops the loop. ...

	This is true. Nonetheless, the difference isn't as great
	as you seem to think. What's really happening here? Pascal
	is giving you a one-record buffer that you can inspect without
	advancing the file pointer. However, we can implement this
	easily enough in Turbo's paradigm, by introducing a buffer
	variable tied to FileVar:

	reset(FileVar)   ->   reset(FileVar); read(FileVar,FileVarP);
	get(FileVar)     ->   read(FileVar,FileVarP);
	FileVar^	 ->   FileVarP

	If you're so inclined, you can bundle the file and the variable
	as fields of a record, and implement some alternate I/O routines
	that give you the abstraction.

	I've converted a number of programs from Standard Pascal to
	Turbo using this approach, and it works fine.

	Now, I agree with everyone else that Borland should not have
	changed the semantics of Pascal, but arguing purely from a
	standpoint of the language, it's a tossup. I certainly wouldn't
	pay anything for the file window abstraction.

	-Andrew

>-- 
>gus Baird