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type 'a state =
| Unset
| Set of 'a
type 'a t =
{ mutable state : 'a state
; to_dyn : 'a -> Dyn.t
}
let create to_dyn = { state = Unset; to_dyn }
let set t new_ =
match t.state with
| Unset -> t.state <- Set new_
| Set old ->
Code_error.raise "Fdecl.set: already set"
[ ("old", t.to_dyn old); ("new_", t.to_dyn new_) ]
let set_idempotent ~equal t new_ =
match t.state with
| Unset -> t.state <- Set new_
| Set old ->
if not (equal new_ old) then
Code_error.raise "Fdecl.set_idempotent: already set to a different value"
[ ("old", t.to_dyn old); ("new_", t.to_dyn new_) ]
let get t =
match t.state with
| Unset -> Code_error.raise "Fdecl.get: not set" []
| Set x -> x