Cookbook/Lists and strings

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Revision as of 12:10, 23 April 2009 by JohannesAhlmann (talk | contribs) (reverse . take . reverse)
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Since strings are lists of characters, you can use any available list function.

Combining strings

Problem Solution Examples
combining two strings (++)
"foo" ++ "bar"                  --> "foobar"
combining many strings concat
concat ["foo", "bar", "baz"]    --> "foobarbaz"

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 TODO 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"

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")

Multiline strings

\bar"               --> "foobar"

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'

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"

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"




For high performance requirements (where you would typically consider C), consider using Data.ByteString.