Lazy(3o) - phpMan

Lazy(3o)                                  OCaml library                                  Lazy(3o)



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:  if the program is compiled with the -rectypes option, ill-founded recursive defini-
       tions 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  -rec-
       types 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  excep-
       tion,  the  same  exception is raised again.  Raise 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 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 lazy_from_fun : (unit -> 'a) -> 'a t


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




       val lazy_from_val : 'a -> 'a t


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




       val lazy_is_val : 'a t -> bool


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






OCamldoc                                    2008-05-19                                   Lazy(3o)

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