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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Queues and barrel rolls in Perl

There are some applications where you want to go round and round a list and one way to do so is to "barrel roll" the list by moving the last element onto the start each time you use an element. That would be complicated in some languages, but in Perl you can simply use a pop followed by an unshift. Thus:

@hehad = ("Chicken","Feta","Rice","Sticky toffee pudding");
unshift @hehad,(pop @hehad);


And if you want a queue - simply push onto a list and unshift off ... once you get a false value back, your queue is empty.
(written 2006-02-24, updated 2006-06-09)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P208 - Perl - Lists
  [28] Perl for breakfast - (2004-08-25)
  [140] Comparison Chart for Perl programmers - list functions - (2004-12-04)
  [230] Course sizes - beware of marketing statistics - (2005-02-27)
  [240] Conventional restraints removed - (2005-03-09)
  [355] Context in Perl - (2005-06-22)
  [463] Splitting the difference - (2005-10-13)
  [560] The fencepost problem - (2006-01-10)
  [762] Huge data files - what happened earlier? - (2006-06-15)
  [773] Breaking bread - (2006-06-22)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [968] Perl - a list or a hash? - (2006-12-06)
  [1304] Last elements in a Perl or Python list - (2007-08-16)
  [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
  [1703] Perl ... adding to a list - end, middle, start - (2008-07-09)
  [1828] Perl - map to process every member of a list (array) - (2008-10-09)
  [1917] Out of memory during array extend - Perl - (2008-12-02)
  [1918] Perl Socket Programming Examples - (2008-12-02)
  [2067] Perl - lists do so much more than arrays - (2009-03-05)
  [2226] Revision / Summary of lists - Perl - (2009-06-10)
  [2295] The dog is not in trouble - (2009-07-17)
  [2484] Finding text and what surrounds it - contextual grep - (2009-10-30)
  [2813] Iterating over a Perl list and changing all items - (2010-06-15)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [2996] Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12)
  [3400] $ is atomic and % and @ are molecular - Perl - (2011-08-20)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3669] Stepping through a list (or an array) in reverse order - (2012-03-23)
  [3870] Writing more maintainable Perl - naming fields from your data records - (2012-09-25)
  [3906] Taking the lead, not the dog, for a walk. - (2012-10-28)
  [3939] Lots of ways of doing the same thing in Perl - list iteration - (2012-12-03)
  [4609] Mapping an array / list without a loop - how to do it in Perl 6 - (2016-01-03)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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