For 2023 - 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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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)) |
Tcl - lappend v concat
In Tcl, you can use the lappend command to add items on to a list, but it doesn't always do exactly what you wish it to. Let's say that I've got two lists - the first containing the early courses of a meal, and the second containing the latter courses. If I append the second list to the first, the second list gets added AS A SINGLE LIST ITEM to the first list ... in the following example, adding the list "also" with two items in it (Fruit and Coffee") to the list "lunch" with two items (Soup and Salad) results in a list of just three items - Soup, Salad and {Fruit Coffee} rather than the four I would have hoped for.
If you want to add each item in the second list on to the end of the first list, you can use the concat command instead of the lappend command. In the following example, concat produces a 4 item list - Soup, Salad, Fruit and Coffee.
set lunch "Soup Salad"
set also "Fruit Coffee"
set first $lunch
lappend first $also
set second $lunch
set rst [concat $second $also]
puts $first
puts $rst
When I runs that ... what do I get?
earth-wind-and-fire:~/jun06 grahamellis$ tclsh ccat
Soup Salad {Fruit Coffee}
Soup Salad Fruit Coffee
earth-wind-and-fire:~/jun06 grahamellis$ (written 2006-06-27)
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) [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) [3394] The difference between lists and strings - Tcl - (2011-08-16) [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)
Some other Articles
Running external processes in Tcl and Tcl/TkWhich way to turn?Good follow up ... my thanksConverting between Hex and Decimal in TclTcl - lappend v concatSeparation and IntegrationThe fragility of pancakes - and better structuresWeekend in IrelandOn Crosby sandsNaming Rooms
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This is a page archived from The Horse's Mouth at
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the diary and writings of Graham Ellis.
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