NAME

       Lazy - Deferred computations.

Module

       Module   Lazy

Documentation

       Module Lazy
        : sig end

       Deferred computations.

       type 'a t = 'a lazy_t

       A  value  of  type  '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 -> 'a

       force  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 Lazy.Undefined if the forcing of x
       tries to force x itself recursively.

       val force_val : 'a t -> 'a

       force_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 Lazy.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
       Lazy.Undefined .

       val from_fun : (unit -> 'a) -> 'a t

       from_fun f is the same as lazy (f ()) but slightly more efficient.

       from_fun should only be used if the function f is already defined.  In  particular  it  is
       always less efficient to write from_fun (fun () -> expr) than lazy expr .

       Since 4.00.0

       val from_val : 'a -> 'a t

       from_val  v returns an already-forced suspension of v .  This is for special purposes only
       and should not be confused with lazy (v) .

       Since 4.00.0

       val is_val : 'a t -> bool

       is_val x returns true if x has already been forced and did not raise an exception.

       Since 4.00.0

       val lazy_from_fun : (unit -> 'a) -> 'a t

       Deprecated.  synonym for from_fun .

       val lazy_from_val : 'a -> 'a t

       Deprecated.  synonym for from_val .

       val lazy_is_val : 'a t -> bool

       Deprecated.  synonym for is_val .