Add `flip foldMap`

[ndmitchell]

Add `flip foldMap`

[ndmitchell]

It seems to be a pattern that these functions come in flipped and non-flipped versions, so it doesn't seem unreasonable. I think the question of what it should be named is probably key. If the name seems to obviously indicate what it does, then it seems good to add. If the name isn't obvious, then it would require people to look up, and probably makes code using it harder to understand. I don't have any good ideas for a name, but I think that's the key question.

[ysangkok]

What about mapMconcat or mapSummarize or mapSummarise or just plain summarize? @cdsmith has referred to mconcat as summarizing: https://cdsmithus.medium.com/monoids-are-composable-list-summarizers-77d2baf23ffc

[cdsmith]

While I did write that article, I don't think the word "summarize" is sufficiently precise to make a good name. Here are some candidates off the top of my head:

• foldEach - this is probably my favorite name in general
• foldFor - because sometimes for is used to mean flip map, though lately it's been more often used for flip traverse instead. A variant is foldOver, since we talk about folding over a list.
• mapFold - I'm not a fan, but it's a sort of flip of foldMap.

[endgame]

I stand by my suggestion of paMdolf, but I think that in the age of -XBlockArguments (GHC >=8.6.1) the need for a distinct function is much lower: Just 3 & foldMap \m -> Sum (m * 2) is actually pretty nice.

[ndmitchell]

Agreed summarise doesn't seem right, since a function called summarise could do almost anything. I'm ok with foldEach/foldFor/mapFold, but have no strong preference on which, or if the function is useful enough with block arguments etc.