[ new ] map-concat

[gallais]

Preparing next year's coursework and I'll need this. :)

[JacquesCarette]

Looks good.

Makes me sad that concat isn't defined in terms of fold so that this could become a special case of map-fold. Ah well.

[jamesmckinna]

Looks good.

Makes me sad that concat isn't defined in terms of fold so that this could become a special case of map-fold. Ah well.

Two things

• the library seemed to prefer direct recursive definitions over higher-order combinators but this (more didactic?) style seems to have gradually been refactored away
• for Vec it's only relatively recently cf. Port reverse lemmas to Data.Vec (fixes #942) #1668 / Port Andreas' work on reverseAcc to vectors too #942 that we've had systematic foldr/foldl fusions

So: possible issue (v3.0? hypothetical-rewrite?) to systematically refactor the whole lot?

[jamesmckinna]

Aaargh... my previous Approve was too hasty...

sheer idiocy/over-hasty reviewing

[jamesmckinna]

Third time's the charm...