Byte array

Many files can be most effectively processed as byte arrays—in F#, we can read byte arrays and create them. The language even has special support for byte arrays.

With the B suffix, on a string literal, we can create a byte array. This is the easiest way to initialize a small byte array for use in an F# program.

Example

This program uses byte arrays in a variety of ways. Because it use a type from the System.IO namespace, it has an "open System.IO" directive at the top.

Part 1 We get a byte array from the disk by calling File.ReadAllBytes. The path will need to be adjusted to point to an existing file.

Part 2 We create a byte array literal. This syntax uses the uppercase "B" at the end of a string literal.

Part 3 We can create a byte array with byte literals with the array initialization syntax.

Part 4 If desired, we can separate each element with a newline instead of a semicolon. The indentation must be correct for this to work.

Part 5 We loop over the elements in a byte array with a for-in loop, printing them as we go along.

Part 6 With Array.map, we add 10 to each element of the array. Then we use Seq.iter to print each value in the new array.

open System.IO

// Part 1: read in file from disk as byte array.
let data = File.ReadAllBytes(@"/Users/sam/programs/output.webp")
printfn $"Data length = {data.Length}"

// Part 2: create a byte array with string syntax.
let data2: byte[] = "cute dog"B
printfn $"Data2 length = {data2.Length}"

// Part 3: create a byte array with integer syntax.
let data3 = [|100; 101; 102; 103|]
printfn $"Data3 length = {data3.Length}"

// Part 4: use separate lines for each value (indentation is important).
let data4 = [|100
              101
              102
              103|]
printfn $"Data4 length = {data4.Length}"

// Part 5: loop over elements in byte array.
for b in data4 do
    printfn $"Byte in data4 = {b}"

// Part 6: add to each element in byte array and print it out with Seq.iter.
let result = Array.map (fun x -> x + 10) data4
result
|> Seq.iter (fun x -> printfn $"Byte in result = {x}")Data length = 4796
Data2 length = 8
Data3 length = 4
Data4 length = 4
Byte in data4 = 100
Byte in data4 = 101
Byte in data4 = 102
Byte in data4 = 103
Byte in result = 110
Byte in result = 111
Byte in result = 112
Byte in result = 113

Byte arrays can be used throughout F# programs in the same way as other arrays. Functions like Array.map can be used with byte arrays.