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7f918cf1 CE |
1 | (* Copyright (C) 2004-2005 Henry Cejtin, Matthew Fluet, Suresh |
2 | * Jagannathan, and Stephen Weeks. | |
3 | * | |
4 | * MLton is released under a BSD-style license. | |
5 | * See the file MLton-LICENSE for details. | |
6 | *) | |
7 | ||
8 | (* | |
9 | * Equatable values can be equated, after which they are equals. Equating | |
10 | * two value requires the client to specify how to compute the new value from | |
11 | * the old. | |
12 | * | |
13 | * Equatable values can be either created by "new" or "delay". In the case of | |
14 | * delay, the value is only computed if "value" is called. | |
15 | * | |
16 | * Equating a value created by delay with a value created by new will completely | |
17 | * drop the delayed value. Hence, if a value is delayed, then nothing should | |
18 | * be assumed about any of its subcomponents. | |
19 | *) | |
20 | ||
21 | signature EQUATABLE = | |
22 | sig | |
23 | type 'a t | |
24 | ||
25 | val equals: 'a t * 'a t -> bool | |
26 | val delay: (unit -> 'a) -> 'a t | |
27 | val equate: 'a t * 'a t * ('a * 'a -> 'a) -> unit | |
28 | val layout: 'a t * ('a -> Layout.t) -> Layout.t | |
29 | val new: 'a -> 'a t | |
30 | val value: 'a t -> 'a | |
31 | val whenComputed: 'a t * ('a -> unit) -> unit | |
32 | end |