[NTG-context] Re: imposition: getting to the last page of a booklet

[Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>]

Pablo Rodriguez via ntg-context schrieb am 06.03.2024 um 20:17:
> On 3/6/24 19:50, Wolfgang Schuster wrote:
>>> [...]
>>> Could you write the first line in plain language?
>>
>> Look at the second example of the Lua code in the example below for each
>> command (the first example is your version), the third example is just a
>> condensed version of example 2.
> 
> Many thanks for your extended explanation, Wolfgang.

Here is another solution which uses \ifcase the select a different case 
dependent on the value of the remainder.

\def\beforequadruplenumber#1%
   {\ifcase\numexpr#1;4\relax
      \the\numexpr#1+3\relax % remainder = 0
    \or
      \the\numexpr#1+2\relax % remainder = 1
    \or
      \the\numexpr#1+1\relax % remainder = 2
    \or
      \the\numexpr#1+4\relax % remainder = 3
    \fi}

\def\afterquadruplenumber#1%
   {\ifcase\numexpr#1;4\relax
      \the\numexpr#1+1\relax % remainder = 0
    \or
      \the\numexpr#1+4\relax % remainder = 1
    \or
      \the\numexpr#1+3\relax % remainder = 2
    \or
      \the\numexpr#1+2\relax % remainder = 3
    \fi}


> Now it is clearer to me (although I need some time to learn from it).

When you use \numexpr to perform arithmetic in TeX it is recommended to 
add a final \relax to stop the command from scanning to additional 
values, e.g. in the example below \testone takes value beyond the 
argument because \numexpr hasn't ended yet.

\starttext

\def\testone#1{\the\numexpr #1 + 1 }

\testone{1} + 1

\def\testtwo#1{\the\numexpr #1 + 1 \relax}

\testtwo{1} + 1

\stoptext

Wolfgang
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