Home Accessibility Courses Diary The Mouth Facebook Resources Site Map About Us Contact
Joining lists in Tcl. Indirect variables in Tcl.

With all programming languages, there seem to be a few things that you end up saying "I'm SURE there's a way to do that" .... yet you can't find out how. Here are two quick solutions in Tcl - a specialist subject, I know, but one of the busiest on our forum.

# Two quick solutions in Tcl ...

# How to join a list onto the end of another list

set first {a b c}
set second {d e f}
set together [concat $first $second]
puts $together

# How to reference a variable named within another variable

set person "John Jones"
set elholder person

# Following line is how NOT to do it - Tcl expands $s just ONCE
set contains $$elholder
puts $contains
# Following line is how you SHOULD do it
set contains [set $elholder]
puts $contains


The concat command lets you concatanate lists. There's a temptation to try to join lists up using the append or lappend commands, but this always turns out to be a bit of a fiddle as you manipulate the list structure yourself, perhaps having to add in extra spaces to the syntax.

Tcl only goes through each command once as it interprets it (it's NOT recursive). That's efficient and what you want most of the time, but just occasionally - for example when you have one variable within another - it's a nuisance. Tcl's set command return the contents of a variable, though, so writing code as in the example above provide a useful is slightly inelegant solution.

We have links to more Tcl List examples and more Tcl interpretter examples available.

(written 2005-02-12, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T202 - Tcl/Tk - Tcl Fundamentals
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [2442] Variable storage - Perl, Tcl and Python compared - (2009-10-08)
  [1469] Curley brackets v double quotes - Tcl, Tk, Expect - (2007-12-12)
  [1426] Buffering up in Tcl - the empty coke can comparison - (2007-11-10)
  [1282] Stringing together Tcl scripts - (2007-07-29)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [362] The ireallyreallywanna operator - (2005-06-28)
  [349] Comments in Tcl - (2005-06-16)
  [328] Making programs easy for any user to start - (2005-05-29)
  [3] Looking for a donkey - (2004-08-05)

T203 - Tcl/Tk - Conditionals and Loops
  [3571] Comparing loop commands in Tcl - (2012-01-06)
  [3570] Trapping errors in Tcl - the safety net that catch provides - (2012-01-06)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3189] Tcl - the danger of square brackets in a while command - (2011-03-02)
  [2681] Tcl - a great engineering language - (2010-03-17)
  [2471] A short form of if ... then ... else - (2009-10-23)
  [2261] Tcl - nice and nasty - (2009-06-29)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [1401] Tcl - using [] or {} for conditions in an if (and while) - (2007-10-23)


Back to
FAQ - Perl or PHP
Previous and next
or
Horse's mouth home
Forward to
Look after your staff and they'll look after you. AOL.
Some other Articles
Futility of war?
Off to Munich
Tcl/Tk (wish) Grid layout example
Look after your staff and they'll look after you. AOL.
Joining lists in Tcl. Indirect variables in Tcl.
FAQ - Perl or PHP
Examples - Gadfly, NI Number, and Tcl to C interface
Canteen Dragon
Fox and Python
PHP5 lets you say no
4252 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86 at 50 posts per page


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.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2014: Well House Manor • 48 Spa Road • Melksham, Wiltshire • United Kingdom • SN12 7NY
PH: 01144 1225 708225 • FAX: 01144 1225 899360 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/210_Join ... -Tcl-.html • PAGE BUILT: Sun Mar 30 15:20:58 2014 • BUILD SYSTEM: WomanWithCat