problem with syms in integral

hey i'm trying this code:

lambda = 2; delta = 3; alpha = 2.5; theta =7; mu = 1; d = 10;

 for k = 1:5
  f2 =@(r)  (((lambda.*pi).^(k.*delta - 1))./factorial(k.*delta - 1)).*(exp(-lambda.*pi.*r.*r)).*( (r.^(2.*k.*delta - alpha)./ (y.^(-alpha)))).*(lambda.*pi.*theta);
 end

   f2 = @(r) (1- 1./(1 + f2(r))).*(lambda.*2.*pi.*r);

   syms r y 
   int(exp(-int(f2,r,y,inf)).*y.*(2.*pi.*lambda.*y.*exp(-pi.*lambda.*y^2)),y,0,inf)

   double(int(exp(-int(f2,r,y,inf)).*y.*(2.*pi.*lambda.*y.*exp(-pi.*lambda.*y.*y)),y,0,inf));

but i get this error:

Error using mupadmex Error in MuPAD command: DOUBLE cannot convert the input expression into a double array. If the input expression contains a symbolic variable, use the VPA function instead.

Error in sym/double (line 514) Xstr = mupadmex('symobj::double', S.s, 0);

Error in test (line 21)

any help ? Thank you