On 1/15/2011 6:41 AM, Nate Knight wrote:
> On Jan 14, 2011, at 12:29 PM, Nate Knight wrote:
>
>> I've pasted some code below where I am trying to transform expressions of
>> the form
>>
>> (a op b op c)[i]
>>
>> to
>>
>> (a[i] op b[i] op c[i])
>>
>> I managed to get this to work for the simple case
>>
>> (a+b)[i]
>>
>> but I'm curious about how to generalize this to include other operators
>> (without explicitly handling them all). Also, as written the transform
>> doesn't recurse properly, and I'm having some trouble seeing how to correct
>> this.
This is a fun little problem. The answer is very simple, but requires
some knowledge of proto's pass_through transform, possessed by
proto::nary_expr (and friends):
// Take any expression and turn each node
// into a subscript expression, using the
// state as the RHS.
struct Distribute
: or_<
when<terminal<_>, _make_subscript(_, _state)>
, nary_expr<_, vararg<Distribute> >
>
{};
struct Vectorize
: or_<
terminal<_>
, when<subscript<_, _>, Distribute(_left, _right)>
, nary_expr<_, vararg<Vectorize> >
>
{};
int main()
{
terminal<char const *>::type a = {"a"};
terminal<char const *>::type b = {"b"};
terminal<char const *>::type c = {"c"};
terminal<int>::type i = {42};
display_expr( (a+b+c)[i] );
display_expr( Vectorize()((a+b+c)[i]) );
}
HTH,
--
Eric Niebler
BoostPro Computing
http://www.boostpro.com
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