On 1/15/2011 6:31 PM, Hossein Haeri wrote:
Dear all,
I have a syntax like
((_1 >> &f1 >> &f2) || (_2 >> &f3) || (_3 >> &f4 >> &f5 >> &f6)) >> g
for which I already have a small grammar which along with my context do their job fine. The above expression is to act like
g(f2(f1(x)), f3(y), f6(f5(f4(z))))
once invoked with _1 == x, _2 == y, and _3 == z. I am currently trying to add a safety layer on top of that which can emit a compile-error -- at the appropriate corner of my code -- that can prevent pass of functions with wrong arities. For example, g above needs to be a ternary.
Although my context will notice it if g is not a ternary and produce a meaningful error message, that's too late. My poor user needs to be informed right at the instantiation time. So, I thought I'm going to use transforms to get my grammar manage that.
<snip>
Below is a grammar Stream that only matches these function stream
expressions where the number of arguments to each callable matches the
arity of the callable. It's a short hop from here to where you want to
be, using is_callable_with_args.
struct FunctionPtr
: proto::and_<
proto::terminal<_>
, proto::if_