gren-lang/core

type String

A String is a chunk of text:

"Hello!"

"How are you?"

"🙈🙉🙊"

-- strings with escape characters
"this\n\t\"that\""

"🙈🙉🙊" -- "🙈🙉🙊"

-- multiline strings
"""Triple double quotes let you
create "multiline strings" which
can have unescaped quotes and newlines.
"""

A String can represent any sequence of unicode characters. You can use the unicode escapes from \u{0000} to \u{10FFFF} to represent characters by their code point. You can also include the unicode characters directly. Using the escapes can be better if you need one of the many whitespace characters with different widths.

Note: JavaScript lets you use double quotes and single quotes interchangably. This is not true in Gren. You must use double quotes for a String, and you must use single quotes for a Char.

isEmpty : String -> Bool

Determine if a string is empty.

isEmpty "" == True

isEmpty "the world" == False

length : String -> Int

Get the length of a string.

length "innumerable" == 11

length "" == 0

reverse : String -> String

Reverse a string.

reverse "stressed" == "desserts"

repeat : Int -> String -> String

Repeat a string n times.

repeat 3 "ha" == "hahaha"

replace : String -> String -> String -> String

Replace all occurrences of some substring.

replace "." "-" "Json.Decode.succeed" == "Json-Decode-succeed"

replace "," "/" "a,b,c,d,e" == "a/b/c/d/e"

Note: If you need more advanced replacements, check out the gren/parser or gren/regex package.

append : String -> String -> String

Append two strings. You can also use the (++) operator to do this.

append "butter" "fly" == "butterfly"

concat : Array String -> String

Concatenate many strings into one.

concat [ "never", "the", "less" ] == "nevertheless"

split : String -> String -> Array String

Split a string using a given separator.

split "," "cat,dog,cow" == [ "cat", "dog", "cow" ]

split "/" "home/evan/Desktop/" == [ "home", "evan", "Desktop", "" ]

join : String -> Array String -> String

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"

words : String -> Array String

Break a string into words, splitting on chunks of whitespace.

words "How are \t you? \n Good?" == [ "How", "are", "you?", "Good?" ]

lines : String -> Array String

Break a string into lines, splitting on newlines.

lines "How are you?\nGood?" == [ "How are you?", "Good?" ]

slice : Int -> Int -> String -> String

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"

left : Int -> String -> String

Take n characters from the left side of a string.

left 2 "Mulder" == "Mu"

right : Int -> String -> String

Take n characters from the right side of a string.

right 2 "Scully" == "ly"

dropLeft : Int -> String -> String

Drop n characters from the left side of a string.

dropLeft 2 "The Lone Gunmen" == "e Lone Gunmen"

dropRight : Int -> String -> String

Drop n characters from the right side of a string.

dropRight 2 "Cigarette Smoking Man" == "Cigarette Smoking M"

contains : String -> String -> Bool

See if the second string contains the first one.

contains "the" "theory" == True

contains "hat" "theory" == False

contains "THE" "theory" == False

startsWith : String -> String -> Bool

See if the second string starts with the first one.

startsWith "the" "theory" == True

startsWith "ory" "theory" == False

endsWith : String -> String -> Bool

See if the second string ends with the first one.

endsWith "the" "theory" == False

endsWith "ory" "theory" == True

indices : String -> String -> Array Int

Get all of the indices for a substring in another string.

indexes "i" "Mississippi" == [ 1, 4, 7, 10 ]

indexes "ss" "Mississippi" == [ 2, 5 ]

indexes "needle" "haystack" == []

toInt : String -> Maybe Int

Try to convert a string into an int, failing on improperly formatted strings.

String.toInt "123" == Just 123

String.toInt "-42" == Just -42

String.toInt "3.1" == Nothing

String.toInt "31a" == Nothing

If you are extracting a number from some raw user input, you will typically want to use Maybe.withDefault to handle bad data:

Maybe.withDefault 0 (String.toInt "42") == 42

Maybe.withDefault 0 (String.toInt "ab") == 0

fromInt : Int -> String

Convert an Int to a String.

String.fromInt 123 == "123"

String.fromInt -42 == "-42"

Check out Debug.toString to convert any value to a string for debugging purposes.

toFloat : String -> Maybe Float

Try to convert a string into a float, failing on improperly formatted strings.

String.toFloat "123" == Just 123.0

String.toFloat "-42" == Just -42.0

String.toFloat "3.1" == Just 3.1

String.toFloat "31a" == Nothing

If you are extracting a number from some raw user input, you will typically want to use Maybe.withDefault to handle bad data:

Maybe.withDefault 0 (String.toFloat "42.5") == 42.5

Maybe.withDefault 0 (String.toFloat "cats") == 0

fromFloat : Float -> String

Convert a Float to a String.

String.fromFloat 123 == "123"

String.fromFloat -42 == "-42"

String.fromFloat 3.9 == "3.9"

Check out Debug.toString to convert any value to a string for debugging purposes.

fromChar : Char -> String

Create a string from a given character.

fromChar 'a' == "a"

cons : Char -> String -> String

Add a character to the beginning of a string.

cons 'T' "he truth is out there" == "The truth is out there"

uncons : String -> Maybe { first : Char, rest : String }

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

toArray : String -> Array Char

Convert a string to a list of characters.

toArray "abc" == [ 'a', 'b', 'c' ]

toArray "🙈🙉🙊" == [ '🙈', '🙉', '🙊' ]

fromArray : Array Char -> String

Convert a list of characters into a String. Can be useful if you want to create a string primarily by consing, perhaps for decoding something.

fromArray [ 'a', 'b', 'c' ] == "abc"

fromArray [ '🙈', '🙉', '🙊' ] == "🙈🙉🙊"

toUpper : String -> String

Convert a string to all upper case. Useful for case-insensitive comparisons and VIRTUAL YELLING.

toUpper "skinner" == "SKINNER"

toLower : String -> String

Convert a string to all lower case. Useful for case-insensitive comparisons.

toLower "X-FILES" == "x-files"

pad : Int -> Char -> String -> String

Pad a string on both sides until it has a given length.

pad 5 ' ' "1" == "  1  "

pad 5 ' ' "11" == "  11 "

pad 5 ' ' "121" == " 121 "

padLeft : Int -> Char -> String -> String

Pad a string on the left until it has a given length.

padLeft 5 '.' "1" == "....1"

padLeft 5 '.' "11" == "...11"

padLeft 5 '.' "121" == "..121"

padRight : Int -> Char -> String -> String

Pad a string on the right until it has a given length.

padRight 5 '.' "1" == "1...."

padRight 5 '.' "11" == "11..."

padRight 5 '.' "121" == "121.."

trim : String -> String

Get rid of whitespace on both sides of a string.

trim "  hats  \n" == "hats"

trimLeft : String -> String

Get rid of whitespace on the left of a string.

trimLeft "  hats  \n" == "hats  \n"

trimRight : String -> String

Get rid of whitespace on the right of a string.

trimRight "  hats  \n" == "  hats"

map : (Char -> Char) -> String -> String

Transform every character in a string

map
    (\c ->
        if c == '/' then
            '.'

        else
            c
    )
    "a/b/c"
    == "a.b.c"

filter : (Char -> Bool) -> String -> String

Keep only the characters that pass the test.

filter isDigit "R2-D2" == "22"

foldl : (Char -> b -> b) -> b -> String -> b

Reduce a string from the left.

foldl cons "" "time" == "emit"

foldr : (Char -> b -> b) -> b -> String -> b

Reduce a string from the right.

foldr cons "" "time" == "time"

any : (Char -> Bool) -> String -> Bool

Determine whether any characters pass the test.

any isDigit "90210" == True

any isDigit "R2-D2" == True

any isDigit "heart" == False

any isDigit "" == False

all : (Char -> Bool) -> String -> Bool

Determine whether all characters pass the test.

all isDigit "90210" == True

all isDigit "R2-D2" == False

all isDigit "heart" == False

all isDigit "" = True

String

Strings

Building and Splitting

Get Substrings

Check for Substrings

Int Conversions

Float Conversions

Char Conversions

Array Conversions

Formatting

Higher-Order Functions