A module internal to Incremental. Users should see Incremental_intf.

An `At_intervals.t` is a kind of DAG node that changes at a regular time interval.

`include module type of sig ... end`
`type t``= Incremental_kernel__Types.At_intervals.t``=` `{`

`main : unit Incremental_kernel__Types.Node.t;`
`base : Incremental_kernel__.Import.Time_ns.t;`
`interval : Incremental_kernel__.Import.Time_ns.Span.t;`
`mutable alarm : Incremental_kernel__Types.Alarm.t;`

`}```
`include Core_kernel.Invariant.S with type t := t`
`type t`````
`val invariant : t Base__.Invariant_intf.inv`
`include Incremental_kernel__.Sexp_of.S with type t := t`
`type t`````
`include sig ... end`
`val sexp_of_t : t ‑> Base.Sexp.t`