Dominique Devriese comments my remark :
Could you mention, please, a system whose measures are for sure positive reals, infinity included? here: I think he's talking about the mathematical notion of measure: https://en.wikipedia.org/wiki/Measure_(mathematics) Gosh, I should have read Olaf Klinke somewhat slower... But I was a physicist too long. Sorry!
On the other hand, I would like to see where, in what kind of computations, the Rig type class would be useful (and how to squeeze infinity into it). I spent some time doing some computations using probabilistic measures and very standard programming standards, and I am conservatist. Of course, as Macchiavelli said in "Prince" (more or less): "the innovator makes enemies of all those who have done well under the old conditions". I am doubtful whether I "did well", but I wait for the innovators to show me their "new conditions". A good example, where a new Prelude with Rigs, Rngs, etc., permit to solve better some concrete, useful computational problems. Thanks in advance. Jerzy Karczmarczuk