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
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
|
module Result
exposing Result(..), is_ok/1, is_none/1, map/2, map_error/2, flatten/1,
flat_map/2, unwrap/2, to_maybe/1, from_maybe/1
import Maybe exposing Maybe(..)
doc """
Result represents the result of something that may succeed or fail.
`Ok` means it was successful, `Error` means it failed.
"""
type Result(error, value) {
| Ok(value)
| Error(error)
; // Fix GitHub syntax highlighting
fn is_ok(result) {
case result {
| Error(_) => False
| Ok(_) => True
}
}
test is_ok {
is_ok(Ok(1)) |> Assert.true
is_ok(Error(1)) |> Assert.false
}
fn is_error(result) {
case result {
| Ok(_) => False
| Error(_) => True
}
}
test is_error {
is_error(Ok(1)) |> Assert.false
is_error(Error(1)) |> Assert.true
}
fn map(result, fun) {
case result {
| Ok(x) => fun(x)
| Error(_) => result
}
}
test map {
map(Ok(1), |x| x + 1) |> Assert.equal(_, Ok(2))
map(Error(1), |x| x + 1) |> Assert.equal(Error(1))
}
fn map_error(result, fun) {
case result {
| Ok(_) => result
| Error(error) => error |> fun |> Error
}
}
test map_error {
map_error(Ok(1), |x| x + 1) |> Assert.equal(_, Ok(1))
map_error(Error(1), |x| x + 1) |> Assert.equal(Error(2))
}
fn flatten(result) {
case result {
| Ok(x) => x
| Error(_) => result
}
}
test flatten {
flatten(Ok(Ok(1))) |> Assert.equal(_, Ok(1))
flatten(Ok(Error(1))) |> Assert.equal(_, Error(1))
flatten(Error(1)) |> Assert.equal(_, Error(1))
}
fn flat_map(result, fun) {
result
|> unwrap(_, fun)
|> flatten
}
test flat_map {
flat_map(Error(1), |x| Ok(x + 1)) |> Assert.equal(_, Error(1))
flat_map(Ok(1), |x| Ok(x + 1)) |> Assert.equal(_, Ok(2))
flat_map(Ok(1), |_| Error(1)) |> Assert.equal(_, Error(1))
}
fn unwrap(result, default) {
case result {
| Ok(v) => v
| Error(_) => default
}
}
test unwrap {
unwrap(Ok(1), 50) |> Assert.equal(_, 1)
unwrap(Error("nope"), 50) |> Assert.equal(_, 50)
}
fn to_maybe(result) {
case result {
| Ok(v) => Just(v)
| Error(_) => Nothing
}
}
test to_maybe {
to_maybe(Ok(1)) |> Assert.equal(_, Just(_, 1))
to_maybe(Error(1)) |> Assert.equal(_, Nothing)
}
fn from_maybe(maybe, error_reason) {
case maybe {
| Just(v) => Ok(v)
| Nothing => Error(error_reason)
}
}
test from_maybe {
to_maybe(Just(1), :ok) |> Assert.equal(_, Ok(1))
to_maybe(Nothing, :ok) |> Assert.equal(_, Error(:ok))
}
|
