[Boost-users] Preprocessor lib question -- how to fold a macro that produces comma in its output across a sequence?

From: Yu Di (diyu60607_at_[hidden])
Date: 2007-10-30 17:41:14

Hi,  I am trying to use the preprocessor lib to generate something like

Cons<a, Cons<b, Cons<c, Cons<d, Nil> > > > 

from 

(a) (b) (c) (d)

I tried something like 

#define START(x) Cons<x,Nil>
#define ADD(s,state,x) Cons<x,state >
#define GENERATE(x) BOOST_PP_SEQ_FOLD_RIGHT(ADD,START(BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_REVERSE(x))),BOOST_PP_SEQ_POP_BACK(x))

but immediately got into trouble with the commas. The best I can do is to add parentheses around the content of START and ADD, but that generated 

(Cons<a, (Cons<b, (Cons<c, (Cons<d, Nil>) >) >) >)

which is not valid. 

Is there any way I can achieve the desired output? Thanks,

Di, Yu
10.30

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