Passing text to Metapost functions

[David Arnold <dwarnold45@cox.net>]

All,

I'd like to do something like this:

create_axes(xmin,xmax,ymin,ymax,ux,uy)(x);

Where x will be a label for my x-axis. But once in a while it might  
be t or u or some other thing such as "Days."

I want to use it like this:

beginfig(0);

%initialize window parameters
numeric xmin, xmax, xscl, ymin, ymax, yscl;
xmin:=-5;
xmax:=5;
xscl:=1;
ymin:=-5;
ymax:=5;
yscl:=1;

%initialize scale
numeric ux, uy;
(xmax-xmin)*ux=4in; (ymax-ymin)*uy=3in;

%create-axes function
vardef create_axes(expr xxmin, xxmax, yymin, yymax, uux, uuy)(text  
xlbl)=
   drawdblarrow (1.05*xxmin*uux,0)--(1.05*xxmax*uux,0);
   label.rt(btex $xlbl$, (1.05*xxmax*uux,0));
   drawdblarrow (0,1.05*yymin*uuy)--(0,1.05*yymax*uuy);
enddef;

create_axes(xmin,xmax,ymin,ymax,ux,uy)(x);

endfig;

end.

Two questions:

1. How can I do this in plain metapost?

2. What would be the "Context Way?"