Cookbook/Lists and strings
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| [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:drop drop], [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:take take] | | [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:drop drop], [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:take take] | ||
| <haskell> | | <haskell> | ||
| - | take 4 $ drop 2 "foo bar baz" | + | take 4 $ drop 2 "foo bar baz" --> "o ba" |
</haskell> | </haskell> | ||
|} | |} | ||
Revision as of 13:10, 23 April 2009
Since strings are lists of characters, you can use any available list function.
Contents |
1 Combining strings
| Problem | Solution | Examples |
|---|---|---|
| combining two strings | (++) | "foo" ++ "bar" --> "foobar" |
| combining many strings | concat | concat ["foo", "bar", "baz"] --> "foobarbaz" |
2 Accessing substrings
| Problem | Solution | Examples |
|---|---|---|
| accessing the first character | head | head "foo bar baz" --> 'f' |
| accessing the last character | last | last "foo bar baz" --> 'z' |
| accessing the character at a given index | (!!) | "foo bar baz" !! 4 --> 'b' |
accessing the first n characters
| take | take 3 "foo bar baz" --> "foo" |
accessing the last n characters
| reverse , take | reverse . take 3 . reverse $ "foobar" --> "bar" |
accessing the n characters starting from index m
| drop, take | take 4 $ drop 2 "foo bar baz" --> "o ba" |
3 Splitting strings
| Problem | Solution | Examples |
|---|---|---|
| splitting a string into a list of words | words | words "foo bar\t baz\n" --> ["foo","bar","baz"] |
| splitting a string into two parts | splitAt | splitAt 3 "foo bar baz" --> ("foo"," bar baz") |
4 Multiline strings
"foo\ \bar" --> "foobar"
5 Converting between characters and values
| Problem | Solution | Examples |
|---|---|---|
| converting a character to a numeric value | ord | import Char ord 'A' --> 65 |
| converting a numeric value to a character | chr | import Char chr 99 --> 'c' |
6 Reversing a string by words or characters
| Problem | Solution | Examples |
|---|---|---|
| reversing a string by characters | reverse | reverse "foo bar baz" --> "zab rab oof" |
| reversing a string by words | words, reverse, unwords | unwords $ reverse $ words "foo bar baz" --> "baz bar foo" |
| reversing a string by characters by words | words, reverse, map, unwords | unwords $ map reverse $ words "foo bar baz" --> "oof rab zab" |
7 Converting case
| Problem | Solution | Examples |
|---|---|---|
| converting a character to upper-case | toUpper | import Char toUpper 'a' --> "A" |
| converting a character to lower-case | toLower | import Char toLower 'A' --> "a" |
| converting a string to upper-case | toUpper, map | import Char map toUpper "Foo Bar" --> "FOO BAR" |
| converting a string to lower-case | toLower, map | import Char map toLower "Foo Bar" --> "foo bar" |
8 Interpolation
TODO
9 Performance
For high performance requirements (where you would typically consider C), consider using Data.ByteString.
10 Unicode
TODO
