Extracting substrings

Elm:
Extracting substrings

How to:

Elm makes it easy. For a start, let’s use String.slice:

import String exposing (slice)

fullText : String
fullText = "Hello, Elm world!"

-- Extracting "Elm"
substring : String
substring = slice 7 10 fullText

-- Output: "Elm"

Now, let’s get a bit more dynamic with String.left and String.right:

import String exposing (left, right)

-- Getting first 5 characters
leftString : String
leftString = left 5 fullText

-- Output: "Hello"

-- Getting last 5 characters
rightString : String
rightString = right 5 fullText

-- Output: "orld!"

Deep Dive

Historically, substring extraction is as old as programming itself. In Elm, as in other functional languages, string manipulation functions are immutable - they return new strings rather than altering the original.

Alternatives like String.dropLeft and String.dropRight exist. They trim characters from either end of the string:

import String exposing (dropLeft, dropRight)

-- Dropping first 7 characters
droppedLeftString : String
droppedLeftString = dropLeft 7 fullText

-- Output: "Elm world!"

-- Dropping last 6 characters
droppedRightString : String
droppedRightString = dropRight 6 fullText

-- Output: "Hello, Elm"

Implementation-wise, these functions are built into the Elm standard library and handle Unicode, though there are considerations to be made with Unicode’s surrogate pairs and combining characters.

Elm:Extracting substrings

How to:

Deep Dive

See Also

Elm:
Extracting substrings