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In this guide, we will discuss String in ELM Programming Language. A sequence of Unicode characters is called a String. In Elm, strings are enclosed in “” double quotes. A String is a chunk of text as shown below.

> "Adglob"
"Adglob" : String
> location = "Hyderabad" --variable
"Hyderabad" : String
> location
"Hyderabad" : String
>

String Functions

Some common functions that can be used to query or manipulate string values are given below. Use REPL to try the examples given below.

isEmpty

This function can be used to determine if a string is empty. This function returns True if the supplied String is empty.

Syntax

String.isEmpty String_value

To check the signature of function, type the following in elm REPL −

> String.isEmpty
<function> : String -> Bool

Signature of the function shows Bool as return type and input type as String −

Illustration

> String.isEmpty ""
True : Bool
> String.isEmpty "Adglob"
False : Bool
> location = "Hyderabad"
"Hyderabad" : String
> String.isEmpty location
False : Bool

reverse

This function reverses a string.

Syntax

String.reverse String_value

To check the signature of function, type the following in elm REPL −

> String.reverse
<function> : String -> String

Signature of the function shows String as return type and input type as String −

Illustration

> String.reverse "Adglob"
"bolgdA" : String

length

This function returns the length of a string.

Syntax

String.length String_value

To check the signature of function, type the following in elm REPL −

> String.length
<function-> : String -> Int

The signature of the function shows Int as return type and input type as String.

Illustration

> String.length "Mohtashim"
9 : Int

append

This function returns a new string by appending two strings.

Syntax

String.append String_value1 String_value2

To check the signature of function, type the following in elm REPL −

> String.append
<function-> : String -> String -> String

Signature of shows two String input parameters and one String output parameter

Illustration

> String.append "Adglob" "Infosystem"
AdglobInfosystem : String

concat

This function returns a new string by concatenating many strings into one.

Syntax

String.concat [String1,String2,String3]

To check the signature of function, type the following in elm REPL −

> String.concat
<function> : List String -> String

Signature of shows a List of String input parameter and String return type

Illustration

> String.concat ["Hello","Adglob","Infosystem"]
HelloAdglobInfosystem : String

split

This function splits a string using a given separator.

Syntax

String.split string_seperator String_value

To check the signature of function, type the following in elm REPL −

> String.split
<function> : String -> String -> List String

Signature of shows two input String parameters and output as a list of string type.

Illustration

> String.split "," "Hello,Adglob,Infosystem"
["Hello","Adglob","Infosystem"] : List String

slice

This function returns a substring given a start and end index. Negative indexes are taken starting from the end of the list. The value of the index starts from zero.

Syntax

String.slice start_index end_index String_value

To check the signature of function, type the following in elm REPL −

> String.slice
<function> : Int -> Int -> String -> String

Signature of shows three input parameter and one return type.

Illustration

> String.slice 0 5 "Adglob"
"Adglo" : String

contains

This function returns a True if the second string contains the first one.

Syntax

String.contains string1 string2

To check the signature of function, type the following in elm REPL −

> String.contains
<function> : String -> String -> Bool

Signature of shows bool return type and two input parameters

Illustration

> String.contains "Infosystem" "Adglob"
True : Bool

toInt

This function converts a string into an int.

Syntax

String.toInt string_value

To check the signature of function, type the following in elm REPL −

> String.toInt
<function> : String -> Result.Result String Int

Since toInt can return error, the return type is Result, which is String or Int.

Illustration

> String.toInt "20"
Ok 20 : Result.Result String Int
> String.toInt "abc"
Err "could not convert string 'abc' to an Int" : Result.Result String Int

toFloat

This function converts a string into a float.

Syntax

String.toFloat string_value

To check the signature of function, type the following in elm REPL −

> String.toFloat
<function> : String -> Result.Result String Float

Since toFloat can return error, the return type is Result, which is String or Float.

Illustration

> String.toFloat "20.50"
Ok 20.5 : Result.Result String Float
> String.toFloat "abc"
Err "could not convert string 'abc' to a Float" : Result.Result String Float

fromChar

This function creates a string from a given character.

Syntax

String.fromChar character_value

To check the signature of function type following in elm REPL −

> String.fromChar
<function> : Char -> String

The signature shows String as return type and input as Char type

Illustration

> String.fromChar 'c'
"c" : String

toList

This function converts a string to a list of characters.

Syntax

String.toList string_value

To check the signature of the function, type the following in elm REPL −

> String.toList
<function> : String -> List Char

The signatures show function returns a list of characters and takes input a string.

Illustration

> String.toList "adglob"
['a','d','g','l','o','b'] : List Char

fromList

This function converts a list of characters into a String.

Syntax

String.fromList list_of_characters

To check the signature of function, type the following in elm REPL −

> String.fromList
<function> : List Char -> String

The signatures shows function returns a list of characters and takes input a string.

Illustration

> String.fromList ['h','e','l','l','o']
"hello" : String

toUpper

This function converts a string to all upper case.

Syntax

String.toUpper String_value

To check the signature of function, type the following in elm REPL −

> String.toUpper
<function> : String -> String

Illustration

> String.toUpper "hello"
"HELLO" : String

toLower

This function converts a string to all lower case.

Syntax

String.toLower String_value

To check the signature of function, type the following in elm REPL −

> String.toLower
<function> : String -> String

Illustration

> String.toLower "AbCd"
"abcd" : String

trim

This function gets rid of whitespace on both sides of a string.

Syntax

String.trim String_value

To check the signature of function, type the following in elm REPL −

> String.trim
<function> : String -> String

Illustration

> String.trim "adglob "
"adglob" : String

filter

This function filters a set of characters from input String. Keep only the characters that pass the test.

Syntax

String.filter test_function string_value

To check the signature of function, type the following in elm REPL −

> String.filter
<function> : (Char -> Bool) -> String -> String

The signature shows filter takes two input parameters and returns a String. The first parameter is a function, which has input Char and returns Bool.

Illustration

In the example, we are passing Char.isUpper as parameter to filter method; it returns all upper-case characters as shown below.

> import Char
> String.filter Char.isUpper "abcDEF"
"DEF" : String

map

This function takes a String and transforms every character in a string.

Syntax

String.filter mapping_function string_value

To check the signature of function, type the following in elm REPL −

> String.map
<function> : (Char -> Char) -> String -> String

Illustration

The following example replaces the character o with @ −

> String.map (\c -> if c == 'o' then '@' else c) "Adglob"
"Adgl@b" : String

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