Comments on: Metalists for fun and profit

By: rmn

rmn — Wed, 17 Feb 2010 19:23:37 +0000

It is perfectly possible to have Reduce result in a type instead of an int (or any other specific type). – This is left as an exercise

Indeed, if Reduce would result in a type then we could implement Map as a Reduce which executes a metafunction on every member and inserts its ‘output’ into the list which is its result. Very nice point!

By: lorg

lorg — Mon, 15 Feb 2010 09:54:08 +0000

I beg to differ, see http://www.paulgraham.com/avg.html for example.

By: haggai

haggai — Mon, 08 Feb 2010 15:16:22 +0000

Can you work with Reduce that outputs types other than int? Than you could implement Map using it.

By: Manuel

Manuel — Mon, 08 Feb 2010 08:12:53 +0000

nadavrot: Greate article, but maybe you could add a mention to [Boost Fusion lists](http://www.boost.org/doc/libs/1_41_0/libs/fusion/doc/html/fusion/container/list.html)? Seems pretty related to whay you present here...

By: NN

NN — Mon, 08 Feb 2010 07:52:22 +0000

Very well.
You have proved again that templates are Turing complete.

Anyway some useful idea.
It is better to follow Boost.MPL naming convention
( http://www.boost.org/doc/libs/1_42_0/libs/mpl/doc/index.html )
and to use the written classes instead of writing your own

E.g. there is boost::mpl::map too
http://www.boost.org/doc/libs/1_42_0/libs/mpl/doc/refmanual/map.html

By: sulfide

sulfide — Mon, 08 Feb 2010 00:11:08 +0000

cept no one really uses lisp in real projects

By: lorg

lorg — Sun, 07 Feb 2010 22:42:40 +0000

I think you just proved Greenspun’s tenth rule again http://en.wikipedia.org/wiki/Greenspun%27s_Tenth_Rule

You could have also called your functions cons, car and cdr…

By: Nadav

Nadav — Sun, 07 Feb 2010 21:59:09 +0000

Thanks Next week we can do the one on PI and SIN.

By: rmn

rmn — Sun, 07 Feb 2010 21:23:29 +0000

Great post Nadav! This is very similar to Alexandrescu's Type Lists. I wonder if anybody could come up with an even crazier use-case for this technique, perhaps something seen in a production code.