On Wed, Jan 05, 2022 at 05:39:49PM +0530, Harendra Kumar wrote:
It is hard to objectively or mathematically prove which option is better.
Well, let's give it a go. One condition that instances might be required to satisfy is do { poke p a; peek p } == do { poke p a; evaluate a } and evaluating these expressions should touch at most `sizeof a` bytes starting from `p`. If further you impose the reasonable condition that `sizeof a` should be as small as possible then this fixes the behaviour of the () instance. (Other reasonable conditions are available.) The existing `Storable ()` instance does *not* satisfy this condition, because it is not sufficiently strict. That's orthogonal to Harendra's complaint though. It does satisfy the "as small as possible" part. On the other hand, despite being no expert of Storable, it seems to me the class exists merely to conveniently read to and write from raw memory. The () instance is useless for this purpose so I'm not sure why it exists. If the purpose of the class were to be a general purpose serialisation API then the () instance *would* make sense, but then we'd also have an (a, b) instance too, which we don't. If it were up to me I probably would not have allowed the `Storable ()` instance, and instead I would have designed a "serialise to a raw buffer" API *on top of* Storable (if that's what people really wanted). Tom (See https://www.stackage.org/haddock/lts-18.21/base-4.14.3.0/Foreign-Storable.ht...)