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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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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))
The difference between lists and strings - Tcl

There's not much difference between lists and strings in Tcl. In fact a list is just a string in a particular format, and if you split a string that contains just letters and spaces into a "list" you may not change anything AT ALL. Which means that if you make a coding error you may not spot it until some of the characters which form a part of the list syntax to handle specials are used within the string.

Here's a listish setup:

  set john {{tom simon ann sophie cindy}}

But when I split that and iterate through the elements,I don't get what I want - strange things happen with the inner { and }. Code:

  set mitems [split $john]
  foreach thing $mitems {
    puts $thing
  }


When I run that, the results I get are:

  {tom
  simon
  ann
  sophie
  cindy}


As my handling of the list of lists wasn't correct .... what would have been better is to have written


  foreach thing $john {
    foreach name $thing {
      puts $name
    }
  }


which would give

  tom
  simon
  ann
  sophie
  cindy


For Perl, Python, Ruby and PHP programmers, who are used to split doing a considerable amount of work, the small step taken by Tcl's split comes as a bit of a surprise, and even people who've been writingTcl for a while can end up scratching their head at extra curly braces which they hadn't expected from code like that above.

I'm teaching Tcl in a couple of weeks ... starting on Tuesday 30th August for delegates new to programming, and the following day for delegates with prior experience of another language - see [here] for a description of that course.
(written 2011-08-16)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T206 - Tcl/Tk - Lists
  [144] Tcl sandwich - lists in Tcl - (2004-12-08)
  [463] Splitting the difference - (2005-10-13)
  [781] Tcl - lappend v concat - (2006-06-27)
  [1282] Stringing together Tcl scripts - (2007-07-29)
  [1283] Generating traffic for network testing - (2007-07-29)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1402] Tcl - append v lappend v concat - (2007-10-23)
  [1405] Sorting in Tcl - lists and arrays - (2007-10-24)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [2468] What are Tcl lists? - (2009-10-22)
  [2472] split and join in tcl and expect - (2009-10-23)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [3415] User defined sorting and other uses of callbacks in Tcl and Tk - (2011-09-02)
  [3582] Tcl collections - lists, dicts and array - (2012-01-16)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [3618] lists and struct::list in Tcl - Introduction to struct::list and examples - (2012-02-18)
  [4209] Lists in Tcl - fundamentals in a commented source code example - (2013-11-16)
  [4454] Everything is a string - even a list - (2015-03-11)
  [4455] Working out distance between places, using OS grid references and a program in Tcl - (2015-03-11)


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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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