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available stored in <code>\recurselevel</code>, before as well as afterand is available for use anywhere within the second parenthesis where <code>whatever we want</code> stufftext is found.
explictly explicitly exit it. Nesting is supported. First we present
System Macros/Loops and Recursion (view source)
Revision as of 15:51, 12 September 2023
, 15:51, 12 September 2023no edit summary
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TeX does not offer us powerfull powerful for-loop mechanisms. On
the other hand its recursion engine is quite unique. We
therefore identify the for-looping macros by this method.
number.
=== <{{cmd>|dorecurse</cmd> }} ===
<texcode>
\dorecurse {n} {whatever we want}
used in situations where Plain TeX's <code>\loop</code> macro
ungracefully fails. The current value of the counter is
<context source="yes">
Both <code>\recurselevel</code> and <code>\recursedepth</code> are
macros. The real conters counters are hidden from the user because
we don't want any interference.
=== {{cmd|doloopoverlist}} ===
<texcode>
\doloopoverlist {a, b, c} {current letter is: “\recursestring”\par}
</texcode>
As the command name reads, it loops over the list values.
<context source=== "yes">\doloopoverlist {a, b, c} {current letter is: “\recursestring”\par}</context> {{cmd|recursestring}} is used instead of {{cmd|recurselevel}}. <context source="yes">dostepwiserecurse\doloopoverlist{\tf,\ss,\tt} {\bgroup\recursestring\doloopoverlist{\rm,\it,\bf,\bi,\sc} {\bgroup\recursestring a̱ḇc̱ a̲b̲c̲\quad\egroup}\egroup\par}</context> It also allows commands, as contained in the previous code snippet. === {{cmd> |dostepwiserecurse}} ===
The simple command <code>\dorecurse</code> is
a special case of the more general:
</texcode>
=== <{{cmd>|doloop</}} {{cmd> <cmd>|exitloop</cmd> }} ===
Sometimes loops are not determined by counters, but by
(a combinations of) conditions. We therefore implement a
straightforward loop, which can only be left when we
a more extensive alternative.
</texcode>
When needed, one can call for <code>\looplevelrecurselevel</code> and<code>\loopdepthrecursedepth</code>.
The loop is executed at least once, so beware of situations
for conditional errors.
=== Recursion and expansion === Using recursion to build tables requires some particular attention: <context source="yes">\bTABLE\bTR\dorecurse{8}{\expanded{\bTD\recurselevel\eTD}}\eTR\eTABLE</context> Multi-dimensional tables offer another illustration: <context source="yes">\bTABLE\dorecurse{8}{ \bTR \dorecurse{5}{\bTD #1,##1 \eTD} \eTR}\eTABLE</context> Alternatively, (mkiv only?) <context source="yes">\bTABLE \dorecurse{8}{\bTR \dorecurse{5}{\bTD \currentTABLErow,\currentTABLEcolumn \eTD} \eTR}\eTABLE</context> For further discussion on loops and expansion, see [[System_Macros/Expansion_Control|Expansion control]] as well as this [http://randomdeterminism.wordpress.com/2009/03/05/tex-programming-the-past-the-present-and-the-future/ blog post]. < '''Prev:''' [[System Macros/Branches and Decisions|Branches & Decisions]] | '''Top:''' [[System Macros]] | '''Next:''' [[System Macros/Action Processing|Action Processing]] > [[Category:ConTeXt programmingProgramming and Databases]][[Category:Inside ConTeXtTools]]
