On Tue, 8 Oct 2019, Rudolf Bahr wrote:
On Sun, Oct 06, 2019 at 10:44:12PM +0200, Wolfgang Schuster wrote:
While it is true that you're free to choose the name for the keys there are
two keys with a special meaning, these two keys are "reset" and "set". The
value of the "reset" key is used before the values in \setvariables are
stored while "set" is used after the values are stored.
Hello Wolfgang,
thank you very much for your detailed answer and your two examples!
Concerning the two keys with a special meaning, "reset" and "set", remains a
question
to me. For what are they good? Does "reset" clear a data area, namespace
perhaps,
before new data are stored there? If they are keys, what is there value or are
they
commands?
Let's start with a simple example:
\setvariables
[dummy]
[
set={AAA},
reset={BBB},
]
\starttext
Hello World!
\setvariables[dummy][key=value]
\stoptext
When the \setvariables[dummy][key=value] is called, it first executes the
value of `reset` key. So the output of the above is
```
Hello World! BBBAAA
```
Now suppose you want to do some calculations based on the value
of passed key. Let's take a variation of the original question, and define
a macro where we can say
\setvariables[exam][points=5]
\setvariables[exam][points=10]
and we can a macro \totalpoints to show the number of points. (There are
probably better ways to do this than setvariables ...)
Here is one way to define it:
\def\totalpoints{0}
\setvariables
[exam]
[
points=0, % This is important.
set={\edef\totalpoints{\the\numexpr(\totalpoints +
\getvariable{exam}{points})\relax}},
]
\starttext
\setvariables[exam][points=5]
\setvariables[exam][points=10]
The exam has \totalpoints\ points.
\stoptext
So, everytime \setvariables is call, the value of the `set` key is
executed. If I set the value of the `set` key to code that updates the
value of `\totalpoints` macro, then I get the desired behavior.
Writing macros as value of a key can be cumbersome to read. So, we can use
setups:
\def\totalpoints{0}
\startsetups updatepoints
\edef\totalpoints{\the\numexpr(\totalpoints +
\getvariable{exam}{points})\relax}
\stopsetups
\setvariables
[exam]
[
points=0,
set=\directsetup{updatepoints},
]
\starttext
\setvariables[exam][points=5]
\setvariables[exam][points=10]
The exam has \totalpoints\ points.
\stoptext
That's it.
Aditya
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