module Lazy:Deferred computations.sig..end
type'at ='a lazy_t
'a Lazy.t is a deferred computation, called
   a suspension, that has a result of type 'a.  The special
   expression syntax lazy (expr) makes a suspension of the
   computation of expr, without computing expr itself yet.
   "Forcing" the suspension will then compute expr and return its
   result.
   Note: lazy_t is the built-in type constructor used by the compiler
   for the lazy keyword.  You should not use it directly.  Always use
   Lazy.t instead.
   Note: Lazy.force is not thread-safe.  If you use this module in
   a multi-threaded program, you will need to add some locks.
   Note: if the program is compiled with the -rectypes option,
   ill-founded recursive definitions of the form let rec x = lazy x
   or let rec x = lazy(lazy(...(lazy x))) are accepted by the type-checker
   and lead, when forced, to ill-formed values that trigger infinite
   loops in the garbage collector and other parts of the run-time system.
   Without the -rectypes option, such ill-founded recursive definitions
   are rejected by the type-checker.
exception Undefined
val force : 'a t -> 'aforce x forces the suspension x and returns its result.
   If x has already been forced, Lazy.force x returns the
   same value again without recomputing it.  If it raised an exception,
   the same exception is raised again.
   Raise Undefined if the forcing of x tries to force x itself
   recursively.val force_val : 'a t -> 'aforce_val x forces the suspension x and returns its
    result.  If x has already been forced, force_val x
    returns the same value again without recomputing it.
    Raise Undefined if the forcing of x tries to force x itself
    recursively.
    If the computation of x raises an exception, it is unspecified
    whether force_val x raises the same exception or Undefined.val from_fun : (unit -> 'a) -> 'a tfrom_fun f is the same as lazy (f ()) but slightly more efficient.val from_val : 'a -> 'a tfrom_val v returns an already-forced suspension of v.
    This is for special purposes only and should not be confused with
    lazy (v).val is_val : 'a t -> boolis_val x returns true if x has already been forced and
    did not raise an exception.val lazy_from_fun : (unit -> 'a) -> 'a tfrom_fun.val lazy_from_val : 'a -> 'a tfrom_val.val lazy_is_val : 'a t -> boolis_val.