Module

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Module DataLocations

• What on earth are DataLocations?!
• Steffen Beyer
• YAPCEurope, London, UK,
• ICA, September 22-24 2000

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Agenda

• What is it good for?
• Example
• How does it work?
• Gory Details
• History
• Questions Answers, Suggestions

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What is it good for?

• Writing (almost) sequential streams of data, with
  some portions to be filled in later, after most
  or all of the stream has already been written -
  without using temporary files
• Web Content Management
• Generating code in large IT projects
• Mailings to multiple recipients
• ...

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Example

• Software Development Environment (Code
  Generators)
• Customer Zeppelin-Caterpillar
• Development Platform Unix
• Tool Language Perl
• Production Platform Mainframe MVS/CICS
• Production Language PL/I
• Costs (just the tools!) approx. 4 man-years

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Example

• See
• file "in.txt"
• file "out.txt"

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How does it work? (1/2)

sdm
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How does it work? (2/2)

• DataLocations are implemented so that they
  behave as if they were an integral part of the
  Perl language
• you can send data to DataLocations with
• "print" like to any other filehandle
• you can read from DataLocations with the
• "ltgt" operator as usual
• DataLocations go out of scope as any other
• Perl object
• DataLocations are fully suited for binary data
• DataLocations can be automatically dumped to
• a file, a pipe, a command etc. when program ends

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Cookie

• You can teach people with your head
• You can kill people with an overhead
• You can overkill people with two overheads

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Gory Details

• See
• file "struct0.pl"
• file "struct1.pl"
• file "struct1.txt"

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• DataLocations are typeglobs, filehandles and
  objects
• at the same time
• The typeglob is blessed into the DataLocations
  class
• The filehandle is tied to the object (i.e., to
  itself,
• because Perl confuses typeglobs and filehandles)
• The typeglob's slots (, _at_, ) contain the
  object's data
• (the "_at_" slot actually contains the user's data)
• Symbolic references are used as "weak references"
• for internal interconnections
• The reference count is adjusted so that the
  Location will
• be destroyed when user's last reference goes out
  of scope
• The symbol table DataLocations is used as
  index
• (for "weak reference" lookups and global
  destruction)

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History

• 80s
• 1988/1989
• July 1997

• Delta macro processor (Delta GmbH)
• ProMAC macro processor (sdm GmbH)
• Perl module DataLocations (Free Software)

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DELTA macro processor

• Product of Delta GmbH
• Macro preprocessor to extend the capabilities of
  COBOL and PL/I
• extendable with the help of a PDL macro
  generator
• very cryptic
• poor performance
• hard-coded memory limits

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ProMAC macro processor

• String interpolation reminding of C preprocessor
• built-in functions comparable to Perl
• Regular expressions (similar to egrep)
• Module concept every subroutine is a separate
  file
• Disastrous performance 100 interpreted (even in
  loops)
• Conceptual weaknesses

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Questions Answers, Suggestions

• Please feel free to ask!
• Suggestions are welcome.

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Another Example

• Web Content Management
• Customer Pentium GCC Group
• (http//www.goof.com/pcg/)
• Contact Marc Lehmann ltpcg_at_goof.comgt
• Application Generating status pages with bug
• reports for different releases and
• branches of development