forked from elm/core
/
String.elm
354 lines (263 loc) · 8.99 KB
/
String.elm
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
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
module String
( isEmpty, length, reverse, repeat
, cons, uncons, fromChar, append, concat, split, join, words, lines
, slice, left, right, dropLeft, dropRight
, contains, startsWith, endsWith, indexes, indices
, toInt, toFloat, toList, fromList
, toUpper, toLower, pad, padLeft, padRight, trim, trimLeft, trimRight
, map, filter, foldl, foldr, any, all
) where
{-| A built-in representation for efficient string manipulation. String literals
are enclosed in `"double quotes"`. Strings are *not* lists of characters.
# Basics
@docs isEmpty, length, reverse, repeat
# Building and Splitting
@docs cons, uncons, fromChar, append, concat, split, join, words, lines
# Get Substrings
@docs slice, left, right, dropLeft, dropRight
# Check for Substrings
@docs contains, startsWith, endsWith, indexes, indices
# Conversions
@docs toInt, toFloat, toList, fromList
# Formatting
Cosmetic operations such as padding with extra characters or trimming whitespace.
@docs toUpper, toLower,
pad, padLeft, padRight,
trim, trimLeft, trimRight
# Higher-Order Functions
@docs map, filter, foldl, foldr, any, all
-}
import Native.String
import Char
import Maybe exposing (Maybe)
import Result exposing (Result)
{-| Determine if a string is empty.
isEmpty "" == True
isEmpty "the world" == False
-}
isEmpty : String -> Bool
isEmpty = Native.String.isEmpty
{-| Add a character to the beginning of a string. -}
cons : Char -> String -> String
cons = Native.String.cons
{-| Create a string from a given character.
fromChar 'a' == "a"
-}
fromChar : Char -> String
fromChar char =
cons char ""
{-| Split a non-empty string into its head and tail. This lets you
pattern match on strings exactly as you would with lists.
uncons "abc" == Just ('a',"bc")
uncons "" == Nothing
-}
uncons : String -> Maybe (Char, String)
uncons = Native.String.uncons
{-| Append two strings. You can also use [the `(++)` operator](Basics#++)
to do this.
append "butter" "fly" == "butterfly"
-}
append : String -> String -> String
append = Native.String.append
{-| Concatenate many strings into one.
concat ["never","the","less"] == "nevertheless"
-}
concat : List String -> String
concat = Native.String.concat
{-| Get the length of a string.
length "innumerable" == 11
length "" == 0
-}
length : String -> Int
length = Native.String.length
{-| Transform every character in a string
map (\c -> if c == '/' then '.' else c) "a/b/c" == "a.b.c"
-}
map : (Char -> Char) -> String -> String
map = Native.String.map
{-| Keep only the characters that satisfy the predicate.
filter isDigit "R2-D2" == "22"
-}
filter : (Char -> Bool) -> String -> String
filter = Native.String.filter
{-| Reverse a string.
reverse "stressed" == "desserts"
-}
reverse : String -> String
reverse = Native.String.reverse
{-| Reduce a string from the left.
foldl cons "" "time" == "emit"
-}
foldl : (Char -> b -> b) -> b -> String -> b
foldl = Native.String.foldl
{-| Reduce a string from the right.
foldr cons "" "time" == "time"
-}
foldr : (Char -> b -> b) -> b -> String -> b
foldr = Native.String.foldr
{-| Split a string using a given separator.
split "," "cat,dog,cow" == ["cat","dog","cow"]
split "/" "home/evan/Desktop/" == ["home","evan","Desktop", ""]
Use `Regex.split` if you need something more flexible.
-}
split : String -> String -> List String
split = Native.String.split
{-| Put many strings together with a given separator.
join "a" ["H","w","ii","n"] == "Hawaiian"
join " " ["cat","dog","cow"] == "cat dog cow"
join "/" ["home","evan","Desktop"] == "home/evan/Desktop"
-}
join : String -> List String -> String
join = Native.String.join
{-| Repeat a string *n* times.
repeat 3 "ha" == "hahaha"
-}
repeat : Int -> String -> String
repeat = Native.String.repeat
{-| Take a substring given a start and end index. Negative indexes
are taken starting from the *end* of the list.
slice 7 9 "snakes on a plane!" == "on"
slice 0 6 "snakes on a plane!" == "snakes"
slice 0 -7 "snakes on a plane!" == "snakes on a"
slice -6 -1 "snakes on a plane!" == "plane"
-}
slice : Int -> Int -> String -> String
slice = Native.String.slice
{-| Take *n* characters from the left side of a string. -}
left : Int -> String -> String
left = Native.String.left
{-| Take *n* characters from the right side of a string. -}
right : Int -> String -> String
right = Native.String.right
{-| Drop *n* characters from the left side of a string. -}
dropLeft : Int -> String -> String
dropLeft = Native.String.dropLeft
{-| Drop *n* characters from the right side of a string. -}
dropRight : Int -> String -> String
dropRight = Native.String.dropRight
{-| Pad a string on both sides until it has a given length.
pad 5 ' ' "1" == " 1 "
pad 5 ' ' "11" == " 11 "
pad 5 ' ' "121" == " 121 "
-}
pad : Int -> Char -> String -> String
pad = Native.String.pad
{-| Pad a string on the left until it has a given length.
padLeft 5 '.' "1" == "....1"
padLeft 5 '.' "11" == "...11"
padLeft 5 '.' "121" == "..121"
-}
padLeft : Int -> Char -> String -> String
padLeft = Native.String.padLeft
{-| Pad a string on the right until it has a given length.
padRight 5 '.' "1" == "1...."
padRight 5 '.' "11" == "11..."
padRight 5 '.' "121" == "121.."
-}
padRight : Int -> Char -> String -> String
padRight = Native.String.padRight
{-| Get rid of whitespace on both sides of a string.
trim " hats \n" == "hats"
-}
trim : String -> String
trim = Native.String.trim
{-| Get rid of whitespace on the left of a string.
trimLeft " hats \n" == "hats \n"
-}
trimLeft : String -> String
trimLeft = Native.String.trimLeft
{-| Get rid of whitespace on the right of a string.
trimRight " hats \n" == " hats"
-}
trimRight : String -> String
trimRight = Native.String.trimRight
{-| Break a string into words, splitting on chunks of whitespace.
words "How are \t you? \n Good?" == ["How","are","you?","Good?"]
-}
words : String -> List String
words = Native.String.words
{-| Break a string into lines, splitting on newlines.
lines "How are you?\nGood?" == ["How are you?", "Good?"]
-}
lines : String -> List String
lines = Native.String.lines
{-| Convert a string to all upper case. Useful for case-insensitive comparisons
and VIRTUAL YELLING.
-}
toUpper : String -> String
toUpper = Native.String.toUpper
{-| Convert a string to all lower case. Useful for case-insensitive comparisons. -}
toLower : String -> String
toLower = Native.String.toLower
{-| Determine whether *any* characters satisfy a predicate.
any isDigit "90210" == True
any isDigit "R2-D2" == True
any isDigit "heart" == False
-}
any : (Char -> Bool) -> String -> Bool
any = Native.String.any
{-| Determine whether *all* characters satisfy a predicate.
all isDigit "90210" == True
all isDigit "R2-D2" == False
all isDigit "heart" == False
-}
all : (Char -> Bool) -> String -> Bool
all = Native.String.all
{-| See if the second string contains the first one.
contains "the" "theory" == True
contains "hat" "theory" == False
contains "THE" "theory" == False
Use `Regex.contains` if you need something more flexible.
-}
contains : String -> String -> Bool
contains = Native.String.contains
{-| See if the second string starts with the first one.
startsWith "the" "theory" == True
startsWith "ory" "theory" == False
-}
startsWith : String -> String -> Bool
startsWith = Native.String.startsWith
{-| See if the second string ends with the first one.
endsWith "the" "theory" == False
endsWith "ory" "theory" == True
-}
endsWith : String -> String -> Bool
endsWith = Native.String.endsWith
{-| Get all of the indexes for a substring in another string.
indexes "i" "Mississippi" == [1,4,7,10]
indexes "ss" "Mississippi" == [2,5]
indexes "needle" "haystack" == []
-}
indexes : String -> String -> List Int
indexes = Native.String.indexes
{-| Alias for `indexes`. -}
indices : String -> String -> List Int
indices = Native.String.indexes
{-| Try to convert a string into an int, failing on improperly formatted strings.
toInt "123" == Ok 123
toInt "-42" == Ok -42
toInt "3.1" == Err "could not convert string '3.1' to an Int"
toInt "31a" == Err "could not convert string '31a' to an Int"
-}
toInt : String -> Result String Int
toInt = Native.String.toInt
{-| Try to convert a string into a float, failing on improperly formatted strings.
toFloat "123" == Ok 123.0
toFloat "-42" == Ok -42.0
toFloat "3.1" == Ok 3.1
toFloat "31a" == Err "could not convert string '31a' to a Float"
-}
toFloat : String -> Result String Float
toFloat = Native.String.toFloat
{-| Convert a string to a list of characters.
toList "abc" == ['a','b','c']
-}
toList : String -> List Char
toList = Native.String.toList
{-| Convert a list of characters into a String. Can be useful if you
want to create a string primarly by consing, perhaps for decoding
something.
fromList ['a','b','c'] == "abc"
-}
fromList : List Char -> String
fromList = Native.String.fromList