Hi Abel, On Feb 2, 2012, at 4:09 PM, Abel Sinkovics wrote:
The do and let notations are general tools for monads - if you need exception propagation only, there is another utility for that in metamonad: the try_ template (http://abel.web.elte.hu/mpllibs/metamonad/try_.html). Instead of writing
template <class T1, ..., class Tn> struct my_metafunction : body {};
you write
template <class T1, ..., class Tn> struct my_metafunction : try_<body> {}; and it instruments body to propagate errors.
If body calls another metafunction then does that one have to be instrumented too?
To support the use case when people don't want to pay for exception propagation, I can extend metamonad the following way: when a macro (eg. DISABLE_TMP_EXCEPTIONS) is defined, try_ becomes the identity metafunction. In that case it will have a minimal cost (1 extra instantiation). What do you think?
That sounds like a good idea but I haven't experimented with the library yet. Your library came up because a recursive depth-first-search isn't interruptible without exceptions, but I'm still not sure whether that means getting rid of recursion or introducing exceptions. Cheers, Gordon