Metapost : input file within macros

Question

I like to have separate .mp files to organize my Metapost projects. But I'm facing this error message when I try to input file within a macro File names can't appear within macros. Even with this very clear message I'm wondering if there is a solution to call input files in a macro ? (package, extension, Metafun, Metafont, little hack, etc. ?)

def init =
    input var.mp
    draw (0,A)--(10,B)--(20,C);
enddef;

beginfig(1);

init;

endfig;
end.

Thank you for your help.

Answer 1

You can use readfrom:

string rf;
def init =
  forever:
    rf:=readfrom "var.mp";
    exitif rf=EOF;
    scantokens(rf);
  endfor
  closefrom "var.mp";
  draw (0,A)--(10,B)--(20,C);
enddef;

beginfig(1);

init;

endfig;
end.