[Gnuplot-info] internal error: stack not empty

[yi lu <luy...@ya...>]

I tried to plot a graph that used mometum against its events.
The graph looks all right but when I tried to run it, it always show internal 
error: stack not empty. 

Here is my script:
reset;
set terminal x11;
set termopt enhanced;
set termopt font "Helvetica,24";
bin_width = 0.25;  # bin width in GeV
bin_number(x) = floor(x/bin_width);
binc(x) = bin_width * ( bin_number(x) + 0.5 );
total_protons = 12500.0;
isType(x,type) = (x==type)
piplus = 8; piminus=9; Kplus = 11; Kminus = 12; KOL= 10; KOS=16;
proton = 14; antiproton = 15; neutron = 13; lambda = 18;
mom(px,py,pz) =  sqrt(px*px+py*py+pz*pz);
tan(px,py,pz)=(sqrt(px*px+py*py)/pz);
datafile =  "~/Desktop/120gev_hg_total_data.txt";
set xlabel "Angle";
set ylabel "Number of pions"; 
bin_width = 1;
plot datafile using (binc(tan($4,$5,$6))):(isType($7,piplus)/total_protons) \
title "{/Symbol p}^{+}" smooth frequency w points;

and attachment is part  of the data
since it is too big