apfelmus@quantentunnel.de wrote:
Albert Y. C. Lai wrote:
If and only if the database is a purely functional immutable data structure, this can be done. [...] Many interesting databases are not purely functional immutable; most reside in the external world and can spontaneously change behind your program's back.
I don't think this is the problem because SQL requests are emitted atomically anyway. The (Query a) monad here has nothing to do with mutability of the data base.
The same clock read twice, each reading atomic, can give two different results. (Cf. the monadic type signature of Data.Time.Clock.getCurrentTime.) The same SELECT to the same database issued twice, each time atomic, can give two different results. These are not referentially transparent. These are not purely functional. The notation is a beauty bonus.