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Re: Preprocessing file input

• To: mathgroup at smc.vnet.net
• Subject: [mg121283] Re: Preprocessing file input
• From: David Bailey <dave at removedbailey.co.uk>
• Date: Wed, 7 Sep 2011 05:40:36 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <j44jkp$8s3$1@smc.vnet.net>

On 06/09/2011 08:55, Wolfgang Windsteiger wrote:
> Hi everyone,
>
> is there some hook for preprocessing expressions when they are read from
> a file. I'm looking for an analogon to $Pre, which applies to each
> expression read from a file. E.g. I have file.m containing
>
> expr1
> expr2
> expr3
>
> and when I do
>
> <<file.m
>
> what I would like to happen is
>
> $PreFile[expr1]
> $PreFile[expr1]
> $PreFile[expr1]
>
> Is there something like $PreFile???
>
> Thanks for any suggestion,
> WW.
>
Not exactly, but if you open the file as an input stream with OpenRead, 
you can read expressions using:

Read[strm,Hold[Expression]]

The expressions are returned unevaluated, wrapped in Hold, so you can 
apply whatever function you want at that point.

David Bailey
http://www.dbaileyconsultancy.co.uk