CODEWITHSUNDEEP
f#f#-interactivef#-3.0
user5282281
user5282281

Reputation:

Correct way of defining option in a type

I am learning F# and trying to create a type called Person with 4 properties. 2 of them (mother and father) are optional but somehow I am receiving compiler error.

type Person = {
    name : string;
    age : int;
    mother: Person option -> Person option;
    father: Person option -> Person option;
}

let defaultPerson = {
    name = ""; 
    age = 0; 
    mother = fun person -> person; 
    father = fun person -> person }

let displayPerson person =
    printfn "Name: %s, Age: %d" person.name person.age

let setName person name = 
    { person with Person.name = name }

let setAge person name = 
    { person with Person.name = name }

let setMother person mother = 
    { person with Person.mother = mother }

let setFather person father = 
    { person with Person.father = father }

But when I try following code, it throws a compiler error:

let mother1 = { 
    Person.name = "Angelica"; 
    age = 47; 
    mother = Option<Person>.None; //mother = None doesn't work 
    father = Option<Person>.None }

Upvotes: 3

Views: 69

Answers (1)

Mark Seemann
Mark Seemann

Reputation: 233150

It's not clear to me why mother and father are defined as functions, but you can set them using the fun keyword, as you already seem to have discovered:

let mother1 = { 
    Person.name = "Angelica"; 
    age = 47; 
    mother = fun _ -> None;
    father = fun _ -> None }

Wouldn't the following be a more sensible definition of Person?

type Person' = {
    Name : string;
    Age : int;
    Mother: Person' option;
    Father: Person' option;
}

This would let you define a value like this:

let mother2 = { 
    Name = "Angelica"; 
    Age = 47; 
    Mother = None;
    Father = None }

Upvotes: 3

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