blob: cb4652aa7f83e952a7058fa3e121a6b8365b121a (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
|
exception Unreachable
fun $ (x, y) = x y
infixr 0 $
fun printLn s = (print s; print "\n")
(* All global values which computations may raise an exception must be
* wrapped in lazy, so that no exception is thrown before custom
* top-level handler is set.
*)
fun lazy thunk =
let
datatype 'a value =
Unevaluated of unit -> 'a |
Evaluated of 'a |
Exn of exn
val value = ref $ Unevaluated thunk
in
fn () =>
case !value of
Unevaluated th =>
let
val x = th () handle e => (value := Exn e; raise e)
in
value := Evaluated x;
x
end
| Evaluated v => v
| Exn e => raise e
end
|
