type 'a tVar.t is a registered environment variable. It's value value may be queried and
modified via the jenga RPC or command line.
val register : ?choices:string list ‑> string ‑> string option tregister name ?choices registers name. If choices is provided, this is
attached as meta information, available when querying.
register_with_default ?default name ?choices is like register except default
is used when the variable is unset, and is also attached as meta information.
Except for the registration of default as meta-info, register_with_default
behaves as: register ?choices name |> map ~f:(Option.value ~default)
An exception is raised if the same name is registered more than once in a reload of the jengaroot.
val register_with_default : ?choices:string list ‑> string ‑> default:string ‑> string tval peek : ?dont_trigger:unit ‑> 'a t ‑> 'apeek t causes modification to t (via RPC or command-line) to trigger a reload of
the jengaroot. To avoid this use Dep.getenv instead.