Understanding inferred type in eio

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Eio.Flow.copy has type #Flow.source -> #Flow.sink -> unit.

Since you’re using socket for both arguments, OCaml infers that socket must be both a source and a sink in this case. Since it doesn’t know a specific name for that type, it just lists the operations such a socket must support.

You could help it out by annotating the type, e.g.

let handler (socket : #Eio.Flow.two_way) _addr =

This is a slightly stronger requirement (a two_way also supports shutdown), but then it would simply report the type using that name.

At least in Vim, asking Merlin for the type twice in a row gives the expanded version in all cases.

Cstruct is discussed at Decide on cstruct vs bytes · Issue #140 · ocaml-multicore/eio · GitHub.

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