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Bugfix/applicative both (fixes #3) #6
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`both` in `ppx_let` is for concurrency but the current implementation forces sequential execution. A concurrent applicative needs lazy evaluation. Since OCaml is strict the monad's type is a simple callback to the underlying type. The methods are straightforward except `apply` which awaits both callbacks concurrently. If its state is empty it stores the underlying value otherwise it applies both for the listener. The `bind` tests expect callbacks to execute sequentially while the `both` tests verify concurrency.
Adds `apply_both` to the `Apply` type class. It seemed perfect because of its symmetry to `apply_first`. Formally `both` is the `Monoidal` equivalent of `apply`. I thought `both` would need `pure` for lifted `map` but it worked without it. I also considered supplying overrides but it's tricky to implement lawfully.
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Nice! thanks for the PR 🙂 |
texastoland
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bothinppx_letis for concurrency but the current implementation forces sequential execution.Test
A concurrent applicative needs lazy evaluation. Since OCaml is strict the monad's type is a simple callback to the underlying type. The methods are straightforward except
applywhich awaits both callbacks concurrently. If its state is empty it stores the underlying value otherwise it applies both for the listener.bind's tests expect callbacks to execute sequentially while theboth's verify concurrency.Implementation
Adds
apply_bothto theApplytype class. It seemed perfect because of its symmetry toapply_first. Formallybothis theMonoidalequivalent ofapply(commonly calledmerge). I thoughtbothwould needpurefor liftedmapbut it worked without it. I also considered supplying overrides but it's tricky to implement lawfully.