Convert

Conversions between types can be done in a variety of ways in F#. As an example, we can convert a String an Int with a parsing method. This is a more efficient representation of the data.

For simple conversions, a cast like downcast or upcast is sufficient. For parsing a string, we use Int32.TryParse. For arrays, Seq.asArray and toArray are helpful.

Convert string to int

To convert a number in a string into an int, we use the Int32.TryParse. Other types like Int64 also have equivalent parsing methods.

open System

// This string contains an Int32.
let test = "100"

// Stores the parsed value from TryParse.
let mutable result = 0

// If TryParse succeeds, value is stored in result.
if Int32.TryParse(test, &result) then
    // Print the parsed value.
    printfn "%A" result
100

Seq.ofArray, toArray

A Seq is powerful: we can use many methods on it, like "where" or "map." With Seq.ofArray we treat an array as a sequence.

// This is a string array.
let candies = [|"chocolate"; "sugar"; "cookie"|]

// Use Seq.ofArray to convert to a seq.
// ... Use Seq.toArray to convert seq to a string array.
let firstLetterC =
    Seq.ofArray candies
    |> Seq.where (fun x -> x.StartsWith("c"))
    |> Seq.toArray

printfn "%A" firstLetterC
[|"chocolate"; "cookie"|]

Option to int

In F# many methods return an option. We can convert the option to a value by testing it with IsSome. If an inner value exists, we then access it with Value.

let numbers = [10; 20; 30]

// The tryFind method returns an option containing an int.
let result = List.tryFind (fun x -> x >= 15) numbers

// See if the option has a value.
if result.IsSome then
    // Convert the option into an Int.
    let number = result.Value
    printfn "%d" number
20

Bool to int

Sometimes we have a bool and want to convert it to an int—usually 1 for true and 0 for false. An inline if-expression can be used to do this.

let code = true

// Convert bool to 1 or 0.
let number = if code then 1
             else 0

printfn "%A" code
printfn "%A" number
true
1

With conversions, we change types of our data so that is it more useful. Ints are more effective when dealing with numeric data than strings containing digits.