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 typedef  boost::fusion::result_of::as_vector<boost::fusion::result_of::transform<  params,make_fixed_or_range>::type>::type  params_fixed_or_range;    -Christopher  It does.  Of course, the return type of fusion::transform contains the compile-time  information required.  Thanks very much,  Now I'll look at spirit (and some magic code to generate the Qi parser for  this new sequence) to fill it up with values from an input stream. 

I have simplified the code to http://codepad.org/NDM2Ub7z I have a couple of needs now: 1. attempt to transform pfr back to params. This should succeed if all elements of the fusion sequence are fixed values and throw an exception if any of them is a range. Should I write this as a free floating function, as a conversion operator? 2. there will be many params types, params_1 .... params_n, each of those structs will yield after a fusion::transform the sequences params_fixed_of_range_1... params_fixed_of_range_n. I need the following behavior (I would write for this a free floating template function, templated on the sequence type : one of the params_fixed_of_range_i): template <typename params_fixed_of_range> void do_work(const params_fixed_of_range& seq_i) { /// /// generate a inner for loop for all the ranges in seq_i /// for e.g., if seq_i contains /// { d1= 5.; d2= 4.0..5.0..0.1; d3=-1.5..1.5..0.6; i4=4..26..1; i5=4; i6=0; i7=0; } /// then I would want to generate the following code, or if impossible /// maybe by runtime recursion /// for (double d2=4.0; d2<=5.0; d2+=0.1) for (double d3=-1.5; d3<=1.5; d3+=0.6) for (unsigned int i4=4; i4<=26; i4+=1) { // I know d1=5. i5=4 i6=0 i7=0 // construct a params frm current d1,d2,d3,i4,i5,i6,i7 // do some work based on params // return value, this will be used to plot graphs } }; This seems very doable with boost.fusion, and extremely complicated and not flexible without it. I realize there are a lot of questions into 1 email but appreciate the help you can give me, Best regards,