1Lazy(3)                          OCaml library                         Lazy(3)
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NAME

6       Lazy - Deferred computations.
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Module

9       Module   Lazy
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Documentation

12       Module Lazy
13        : sig end
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16       Deferred computations.
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23       type 'a t = 'a lazy_t
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26       A  value  of type 'a Lazy.t is a deferred computation, called a suspen‐
27       sion, that has a result of type 'a .   The  special  expression  syntax
28       lazy  (expr)  makes  a  suspension of the computation of expr , without
29       computing expr itself yet.  "Forcing" the suspension will then  compute
30       expr and return its result.
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32       Note:  lazy_t is the built-in type constructor used by the compiler for
33       the lazy keyword.  You should not use it directly.  Always  use  Lazy.t
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36       Note: if the program is compiled with the -rectypes option, ill-founded
37       recursive definitions of the form let rec x = lazy x or  let  rec  x  =
38       lazy(lazy(...(lazy x))) are accepted by the type-checker and lead, when
39       forced, to ill-formed values that trigger infinite loops in the garbage
40       collector  and  other  parts of the run-time system.  Without the -rec‐
41       types option, such ill-founded recursive definitions  are  rejected  by
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47       exception Undefined
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53       val force : 'a t -> 'a
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56       force  x  forces  the  suspension  x  and returns its result.  If x has
57       already been forced, Lazy.force x returns the same value again  without
58       recomputing  it.   If  it  raised  an  exception, the same exception is
59       raised again.  Raise Undefined if the forcing of x  tries  to  force  x
60       itself recursively.
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65       val force_val : 'a t -> 'a
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68       force_val  x  forces the suspension x and returns its result.  If x has
69       already been forced, force_val x returns the same value  again  without
70       recomputing  it.   Raise Undefined if the forcing of x tries to force x
71       itself recursively.  If the computation of x raises an exception, it is
72       unspecified  whether force_val x raises the same exception or Undefined
73       .
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78       val lazy_from_fun : (unit -> 'a) -> 'a t
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81       lazy_from_fun f is the same as lazy (f ()) but slightly more efficient.
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86       val lazy_from_val : 'a -> 'a t
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89       lazy_from_val v returns an already-forced suspension of v This  is  for
90       special purposes only and should not be confused with lazy (v) .
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95       val lazy_is_val : 'a t -> bool
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98       lazy_is_val  x  returns  true  if x has already been forced and did not
99       raise an exception.
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106OCamldoc                          2007-05-24                           Lazy(3)