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
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
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 {
Ok(1)
|> map(_, fn(x) { x + 1 })
|> Assert.equal(_, Ok(2))
Error(1)
|> map(_, fn(x) { x + 1 })
|> Assert.equal(Error(1))
}
fn map_error(result, fun) {
case result {
| Ok(_) => result
| Error(error) => Error(fun(error))
}
}
test map_error {
Ok(1)
|> map_error(_, fn(x) { x + 1 })
|> Assert.equal(_, Ok(1))
Error(1)
|> map_error(_, fn(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 {
Error(1)
|> flat_map(_, fn(x) { Ok(x + 1) })
|> Assert.equal(_, Error(1))
Ok(1)
|> flat_map(_, fn(x) { Ok(x + 1) })
|> Assert.equal(_, Ok(2))
Ok(1)
|> flat_map(_, fn(_) { 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))
}
|
