Question regarding loops and CAR: #:G18223 is not a list

Hello, all.  I'm somewhat new to maxima, although I used to work with  
scheme a long long time ago.  I'm working on a program to brute force  
solve a system of equations for a variety of values in order to graph  
it later, but keep running into the error "CAR: #:G18223 is not a list"  
inside my for loops (I'm incrementing across two variables).  Below is  
the offending code.  What about loop structure am I fundamentally  
missing?

-Jarrett

<code>
/*constants*/
a:1;
r:10;
l:1;
/*loop through each value of dmax */
for dmax in [1,0.5,0.01] do
   /*loop through each value of b we're using*/
(  for b: 0 thru 1 step .5 do
   	(s:  
solve([d=dmax-dmax*a*((s-1)/r),sl=s-l*d*s,sr=sl+(r-sl)*d,s=sr- 
sr*b*((sr-1)/r)],[d,s,sl,sr]),

   	/*print results */
   	/*I realize that I'm going to need to sort through the matrix s, but  
this
   	is just a first version of the program */
   	print("s,")
   	)
  );

</code>