[metapost] problem with macro parameters

[Stephan Hennig]

Hi,

while working with metaobj I tried to define a short hand macro for a
call to

nccurve(a)(b) "angleA(ra)", "angleB(rb)";

However, ra and rb (entering and leaving angles at nodes a and b)
evaluate to zero when called inside my macro. I even tried with
scantokens. Although, the string looks ok to me, that gives a lot of
error messages. Any ideas?

Regards,
Stephan Hennig


input metaobj
prologues := 1;

% Alias macro for nccurve(a)(b) "angleA(ra)", "angleB(rb)";
def curve(suffix a,b)(expr ra,rb) =
%% ra and rb evaluate to zero here.
  nccurve(a)(b) "angleA(ra)", "angleB(rb)";
enddef;

def curveS(suffix a,b)(expr ra,rb) =
%% Alternatively tried with scantokens, but this fails.
%% Do I have to expand a and b?
  save s;
  string s;
  s = "nccurve(a)(b) " &
    char(34) & "angleA(" & decimal ra & ")" & char(34) & ", " &
    char(34) & "angleB(" & decimal rb & ")" & char(34) & ";";
  show s;
  scantokens(s);
endgroup
enddef;

beginfig(1);
  newCircle.source("S");
  newCircle.sink("T");
  source.c = (0bp, 0bp);
  sink.c = (100bp, 0bp);
  drawObj(source, sink);
%% This works (red arc).
  nccurve(source)(sink) "angleA(20)", "angleB(-20)", "linecolor(red)";
%% This draws only a simple line (black arc).
  curve(source,sink, 20,-20);
endfig;
end