NAME

       Stdlib.Lazy - no description

Module

       Module   Stdlib.Lazy

Documentation

       Module Lazy
        : (module Stdlib__lazy)

       type 'a t = 'a CamlinternalLazy.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. Matching a suspension with  the  special  pattern
       syntax  lazy(pattern)  also  computes  the  underlying  expression and tries to bind it to
       pattern :

       let lazy_option_map f x = match x with | lazy (Some x) -> Some (Lazy.force f  x)  |  _  ->
       None

       Note:  If  lazy  patterns appear in multiple cases in a pattern-matching, lazy expressions
       may be forced even outside of the case ultimately selected by the pattern matching. In the
       example above, the suspension x is always computed.

       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 .