Re: [NTG-context] Metafun : save memory content ?

20 Jul 2022

      Dear Bruce, dear list,
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Le 19 juill. 2022 à 07:42, Bruce Horrocks  a écrit :
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On 19 Jul 2022, at 04:28, Fabrice L via ntg-context  wrote:
Complementary question : I saw that the « pos_a » « pos_b » of the example could not take numerical value, for example pos_1, pos_2.. How can I use metafun to write a macro to save the contents of hundreds of variable in this object, something like :
getparameters "MyData » [
  for i=1 upto 100 :
      pos_decimal(i) = ThePosition[i],
  endfor ;
] ;
If this is possible, then this is wonderful and open news doors !
I've adapted this example from the metafun-p manual by adding some "write" statements.
I have read the manuals, but not enough it seems ! I missed this part ! I completely miss the «write to » and « read from » instructions. Even a research on the web before posting did not return something interesting. I guess I did not used the good terms, because now, I find some ressources about these functions !
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\starttext
\startMPpage
numeric done[][], i, j, n ; n := 0 ;
forever :
  i := round(uniformdeviate(10)) ;
  j := round(uniformdeviate(10)) ;
  if unknown done[i][j] :
      drawdot
      	(i*cm,j*cm)
      	withpen pencircle scaled 0.5cm
      	withcolor darkred;
      n := n + 1 ;
      done[i][j] := n ;
write "done[" & tostring(i) & "][" & tostring(j) & "] := " & tostring(n) & " ;" to "mp_test_file.txt" ;
fi ;
  exitif n = 10 ;
endfor ;
write EOF to "mp_test_file.txt" ;
\stopMPpage
\stoptext
This results in the expected graphic but also a local file (in the same directory as the source) called "mp_test_file.txt" that contains:
done[9][1] := 1 ;
done[4][3] := 2 ;
done[5][3] := 3 ;
done[5][1] := 4 ;
done[2][9] := 5 ;
done[8][6] := 6 ;
done[9][10] := 7 ;
done[9][7] := 8 ;
done[10][2] := 9 ;
done[6][5] := 10 ;
I think, with a bit of judicious use of "write" statements to add some ConTeXt / MP setup code, it would be possible to include the output from the previous run as MP source of the next run.
Hope this helps, or at least provides some food for thought.
Totally, a lot of food  ! Here is my yesterday example with these functions : 

\starttext
\startMPpage
pair ThePosition[];
ThePosition[1] := (0,0) ;
ThePosition[2] := (10,10) ;
draw ThePosition[1] -- ThePosition[2] ;

% Save the position into a file "bruce.mp"
for i=1 upto 2:
  write "ThePosition[" & tostring(i) & "] := (" & tostring(xpart(ThePosition[i])) & ","& tostring(ypart(ThePosition[i])) &") ;" to "bruce.mp" ;
endfor;
write EOF to "bruce.mp" ;
\stopMPpage

% The external file would like like (comment added manually here):
% ThePosition[1] := (0,0) ;
% ThePosition[2] := (10,10) ;

% We modify the value of ThePosition[2] 
\startMPpage
ThePosition[2] := (10,0) ;
draw ThePosition[1] -- ThePosition[2] ;
\stopMPpage

% We now read the value of ThePosition[2] from the file 
\startMPpage
input "bruce.mp";
% Save the data from the external file 
draw ThePosition[1] -- ThePosition[2] ;

\stopMPpage

\stoptext
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(Note you need to delete the mp_test_file.txt before re-running else it fails.)
So this totally do the trick : once again, magic is happening ! 
Note that in my installation, I do not need to delete the external file.
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—
Bruce Horrocks
Hampshire, UK
Thanks a lot ! 
Fabrice.
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