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

6       Stdlib.Lazy - no description
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Module

9       Module   Stdlib.Lazy
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Documentation

12       Module Lazy
13        : (module Stdlib__lazy)
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21       type 'a t = 'a CamlinternalLazy.t
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24       A  value  of type 'a Lazy.t is a deferred computation, called a suspen‐
25       sion, that has a result of type 'a .   The  special  expression  syntax
26       lazy  (expr)  makes  a  suspension of the computation of expr , without
27       computing expr itself yet.  "Forcing" the suspension will then  compute
28       expr and return its result. Matching a suspension with the special pat‐
29       tern syntax lazy(pattern) also computes the underlying  expression  and
30       tries to bind it to pattern :
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33       let  lazy_option_map  f  x  =  match  x  with  |  lazy (Some x) -> Some
34       (Lazy.force f x) | _ -> None
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36       Note: If lazy patterns appear in multiple cases in a  pattern-matching,
37       lazy  expressions  may  be  forced  even outside of the case ultimately
38       selected by the pattern matching. In the example above, the  suspension
39       x is always computed.
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41       Note:  lazy_t is the built-in type constructor used by the compiler for
42       the lazy keyword.  You should not use it directly.  Always  use  Lazy.t
43       instead.
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45       Note:  Lazy.force  is  not  thread-safe.   If  you use this module in a
46       multi-threaded program, you will need to add some locks.
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48       Note: if the program is compiled with the -rectypes option, ill-founded
49       recursive  definitions  of  the  form let rec x = lazy x or let rec x =
50       lazy(lazy(...(lazy x))) are accepted by the type-checker and lead, when
51       forced, to ill-formed values that trigger infinite loops in the garbage
52       collector and other parts of the run-time system.   Without  the  -rec‐
53       types  option,  such  ill-founded recursive definitions are rejected by
54       the type-checker.
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58       exception Undefined
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64       val force : 'a t -> 'a
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67       force x forces the suspension x and  returns  its  result.   If  x  has
68       already  been forced, Lazy.force x returns the same value again without
69       recomputing it.  If it raised  an  exception,  the  same  exception  is
70       raised  again.  Raise Lazy.Undefined if the forcing of x tries to force
71       x itself recursively.
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75       val force_val : 'a t -> 'a
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78       force_val x forces the suspension x and returns its result.  If  x  has
79       already  been  forced, force_val x returns the same value again without
80       recomputing it.  Raise Lazy.Undefined if the  forcing  of  x  tries  to
81       force  x  itself recursively.  If the computation of x raises an excep‐
82       tion, it is unspecified whether force_val x raises the  same  exception
83       or Lazy.Undefined .
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87       val from_fun : (unit -> 'a) -> 'a t
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90       from_fun f is the same as lazy (f ()) but slightly more efficient.
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93       from_fun  should only be used if the function f is already defined.  In
94       particular it is always less efficient to write  from_fun  (fun  ()  ->
95       expr) than lazy expr .
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98       Since 4.00.0
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102       val from_val : 'a -> 'a t
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105       from_val  v  returns  an  already-forced suspension of v .  This is for
106       special purposes only and should not be confused with lazy (v) .
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109       Since 4.00.0
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113       val is_val : 'a t -> bool
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116       is_val x returns true if x has already been forced and did not raise an
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120       Since 4.00.0
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124       val lazy_from_fun : (unit -> 'a) -> 'a t
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126       Deprecated.  synonym for from_fun .
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130       val lazy_from_val : 'a -> 'a t
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132       Deprecated.  synonym for from_val .
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136       val lazy_is_val : 'a t -> bool
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138       Deprecated.  synonym for is_val .
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144OCamldoc                          2019-07-30                    Stdlib.Lazy(3)