Hi Gordon, "Nested Lambda Expressions with Let Expressions in C++ Template Metaprograms" explains metamonad's lambda expressions. The major difference between that approach and MPL's lambda expressions is that metamonad lambda expressions let the user specify the name of the arguments instead of calling them _1, _2, etc. Using these lambda expressions I could embed lambda expressions inside other lambda expressions. The implementation of do-syntax relies on these lambda expressions as well. I'm not aware of techniques based on monads that help implementing data-structues. They are good at abstracting behaviours (error handling, non-determinism, etc.), they should help you with error propagation in your algorithms (see compile-time exceptions in metamonad). I've done a measurement: I've called "lazy_eval_if" / "eval_if + eager condition evaluation" 1000 times (1.6GHz Atom processors, 1 GB memory, Linux, GCC 4.5.2) and measured the compilation speed with "time". Here are the results: lazy_eval_if: 3.89 s eval_if: 3.65 s As you can see, there is some overhead (lazy_eval_if uses eval_if), however it may be different with other compilers. Regards, Abel Am Freitag, den 09.09.2011, 20:05 -0400 schrieb Gordon Woodhull:
On Sep 9, 2011, at 5:12 PM, Gordon Woodhull wrote:
Okay I have read
Functional Extensions to the Boost Metaprogram Library
Now I get it, lazy extensions for MPL, and all the other goodies you would expect from a haskell-like functional programming library.
And now monads too.
Bravo! I hope you bring these libraries to Boost. I crave the simpler syntax and ability to create more complex of pure lazy evaluation.
Have you measured compilation performance versus more-eager MPL implementations of the same algorithms, to see how bad the abstraction penalty is?
I am looking at porting various Boost.Graph algorithms to my proposed MPL.Graph. Do I understand that monads will help me define metadata structures like heaps and forests that don't seem to "map" easily to functional programming?
Cheers, Gordon
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