Elm - Records

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The record data structure in Elm can be used to represent data as key-value pairs. A record can be used to organize related data to enable easy access and updating data. Elm records are similar to objects in JavaScript. Data elements in a record are known as fields.

Defining a Record

Use the following syntax to define a record −

Syntax

record_name = {fieldname1 = value1, fieldname2 = value2....fieldnameN = valueN}

A record can store data of multiple types. The field names in a record must conform to the general rules for naming an Elm identifier.

Accessing record values

Use the following syntax to access individual fields in a record.

Syntax

record_name.fieldname

OR

.fieldname record_name

Illustration

Try the following in the Elm REPL −

> company = {name="Howcodex",rating=4.5}
{ name = "Howcodex", rating = 4.5 } : { name : String, rating : Float }
> company.name
"Howcodex" : String
> .rating company
4.5 : Float

Using Record with List

A record can be stored inside a list. All field values of the record should be of the same type.

Syntax

list_name = [ {field_name1 = value1},{field_name1 = value2}]

OR

list_name = [record_name1, record_name2, record_name3....record_nameN]

Illustration

Try the following in Elm REPL −

> [{name = "Mohtashim"},{name = "kannan"}]
[{ name = "Mohtashim" },{ name = "kannan" }] : List { name : String }
> record1 = {name = "FirstRecord"}
{ name = "FirstRecord" } : { name : String }
> record2 = {name = "SecondRecord"}
{ name = "SecondRecord" } : { name : String }
> recordList = [record1,record2]
[{ name = "FirstRecord" },{ name = "SecondRecord" }] : List { name : String }

Update a Record

Records are immutable in Elm. When a record is updated, a new record with updated values is returned. The field can hold value of a different type when updating a record.

Syntax

{record_name | field_name1 = new_value1, field_name2 = new_value2,field_name3 = new_value3....field_nameN = new_valueN}

Illustration

Try the following in Elm REPL −

> record1 = {name="FirstRecord"}
{ name = "FirstRecord" } : { name : String }
> record1_updated = {record1 | name = "FirstRecordUpdate"}
{ name = "FirstRecordUpdate" } : { name : String }
> record1
{ name = "FirstRecord" } : { name : String }
> record1 == record1_updated
False : Bool

Illustration

The following example updates multiple fields of a record. Try the following in Elm REPL −

> record3 = {a = 1,b = 2,c = 3,d = 4,e = 5}
{ a = 1, b = 2, c = 3, d = 4, e = 5 }
: { a : number, b : number1, c : number2, d : number3, e : number4 }
> record4 = {record3 | d=400 ,e=500}
{ a = 1, b = 2, c = 3, d = 400, e = 500 }
: { a : number2, b : number3, c : number4, d : number, e : number1 }
>

Types alias

Type alias defines a schema for a record. In other words, a type alias defines which fields can the record store and the type of value these fields can store. Therefore, programmer will not make mistake of missing any specific attribute while assigning values.

Syntax

type alias alias_name = {field_name1:data_type,field_name2:data_type,....field_nameN:data_type}

Illustration

Execute the following in Elm REPL −

> type alias Developer = { name:String,location:String,age:Int}
> dev1 = Developer "kannan" "Mumbai" 20
{ name = "kannan", location = "Mumbai", age = 20 } : Repl.Developer
> dev2 = Developer "mohtashim" "hyderabad" 20
{ name = "mohtashim", location = "hyderabad", age = 20 } : Repl.Developer
>

Now if you forget to type location and age, the statement returns a function, which has input parameters for location and age fields.

> dev3 = Developer "Bhagavati"
<function> : String -> Int -> Repl.Developer
We can invoke the function as shown below and pass to it the values for location and age fields.
> dev3 "Pune" 25
{ name = "Bhagavati", location = "Pune", age = 25 } : Repl.Developer
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