Option pipelines in F#

map, filter and defaultValue chain maybes with no null checks.

// Option.map and bind chain maybes without a single null check.
let inventory = Map [ "Willow", 14; "Bramble", 3 ]

let jarsFor hive = inventory |> Map.tryFind hive

let shipping hive =
    hive
    |> jarsFor
    |> Option.filter (fun jars -> jars >= 6)
    |> Option.map (fun jars -> sprintf "%s ships %d jars" hive jars)
    |> Option.defaultValue (sprintf "%s holds its stock" hive)

["Willow"; "Bramble"; "Thistle"]
|> List.iter (shipping >> printfn "%s")

How it works

1. Map.tryFind starts the chain with an Option.
2. Option.filter turns a weak answer back into None.
3. defaultValue lands the chain on solid ground.

Keywords and builtins used here

• fun
• let

The run, in numbers

Lines

14

Characters to type

441

Tokens

106

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 98 seconds.

Type this snippet

Step 3 of 3 in Idioms, step 21 of 27 in Language basics.

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