6.2 Effects

Effect	What it permits
`io`	files, processes, environment variables, stdout/stderr
`net`	network: rpc, streams, actors, cluster, HTTP
`db`	ORM, `std.kv`, the built-in storage
`time`	reading clocks, `sleep`, timers
`rand`	random numbers

The set of effects is written after the return type, comma-separated: -> User | NotFound net, db. pure is the empty set.
A function MAY call only functions whose effects are included in its set. A violation is a compile error.
The effects of private functions are inferred. pub(api) functions MUST declare their effects explicitly (or pure).
Effect polymorphism: fn map<T, U, effect F>(xs: List<T>, f: fn(T) -> U F) -> List<U> F.
A panic is not an effect and is possible in any function.
A function with any of the effects io, net, db, time is suspendable: it may yield the thread to the scheduler (§8.2). pure and rand functions do not suspend.

Related diagnostics