1Lazy(3)                          OCaml library                         Lazy(3)
2
3
4

NAME

6       Lazy - Deferred computations.
7

Module

9       Module   Lazy
10

Documentation

12       Module Lazy
13        : sig end
14
15
16       Deferred computations.
17
18
19
20
21
22       type 'a t = 'a lazy_t
23
24
25       A  value  of type 'a Lazy.t is a deferred computation, called a suspen‐
26       sion, that has a result of type 'a .   The  special  expression  syntax
27       lazy  (expr)  makes  a  suspension of the computation of expr , without
28       computing expr itself yet.  "Forcing" the suspension will then  compute
29       expr and return its result.
30
31       Note:  lazy_t is the built-in type constructor used by the compiler for
32       the lazy keyword.  You should not use it directly.  Always  use  Lazy.t
33       instead.
34
35       Note:  Lazy.force  is  not  thread-safe.   If  you use this module in a
36       multi-threaded program, you will need to add some locks.
37
38       Note: if the program is compiled with the -rectypes option, ill-founded
39       recursive  definitions  of  the  form let rec x = lazy x or let rec x =
40       lazy(lazy(...(lazy x))) are accepted by the type-checker and lead, when
41       forced, to ill-formed values that trigger infinite loops in the garbage
42       collector and other parts of the run-time system.   Without  the  -rec‐
43       types  option,  such  ill-founded recursive definitions are rejected by
44       the type-checker.
45
46
47
48       exception Undefined
49
50
51
52
53
54       val force : 'a t -> 'a
55
56
57       force x forces the suspension x and  returns  its  result.   If  x  has
58       already  been forced, Lazy.force x returns the same value again without
59       recomputing it.  If it raised  an  exception,  the  same  exception  is
60       raised  again.  Raise Lazy.Undefined if the forcing of x tries to force
61       x itself recursively.
62
63
64
65       val force_val : 'a t -> 'a
66
67
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 Lazy.Undefined if the  forcing  of  x  tries  to
71       force  x  itself recursively.  If the computation of x raises an excep‐
72       tion, it is unspecified whether force_val x raises the  same  exception
73       or Lazy.Undefined .
74
75
76
77       val from_fun : (unit -> 'a) -> 'a t
78
79
80       from_fun f is the same as lazy (f ()) but slightly more efficient.
81
82
83       from_fun  should only be used if the function f is already defined.  In
84       particular it is always less efficient to write  from_fun  (fun  ()  ->
85       expr) than lazy expr .
86
87
88       Since 4.00.0
89
90
91
92       val from_val : 'a -> 'a t
93
94
95       from_val  v  returns  an  already-forced suspension of v .  This is for
96       special purposes only and should not be confused with lazy (v) .
97
98
99       Since 4.00.0
100
101
102
103       val is_val : 'a t -> bool
104
105
106       is_val x returns true if x has already been forced and did not raise an
107       exception.
108
109
110       Since 4.00.0
111
112
113
114       val lazy_from_fun : (unit -> 'a) -> 'a t
115
116       Deprecated.  synonym for from_fun .
117
118
119
120       val lazy_from_val : 'a -> 'a t
121
122       Deprecated.  synonym for from_val .
123
124
125
126       val lazy_is_val : 'a t -> bool
127
128       Deprecated.  synonym for is_val .
129
130
131
132
133
134OCamldoc                          2018-07-14                           Lazy(3)
Impressum