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F# / Bindings and Types

Discriminated unions

Learn Discriminated unions in F# through a focused explanation, a dedicated topic-specific example, an engineering boundary, and a mastery check.

10 min read • Beginner

Discriminated unions is a focused F# lesson inside Bindings and Types. The example uses the construct named in the lesson directly rather than reusing a generic placeholder.

Trace the example from its inputs through Discriminated unions and identify the behavior that would change if that construct were removed or replaced. Pay attention to the language-specific rules shown by the syntax, because neighboring lessons intentionally exercise different mechanisms.

Topic-specific example

fsharp-0009-58fc71f53f.fsx
fsharp Try It Live 
type Payment =
    | Cash of decimal
    | Card of last4:string * amount:decimal

let payment = Card("4242", 89.5M)
printfn "%A" payment
Edge case / engineering note

For Discriminated unions, test one realistic boundary: empty data, invalid input, unavailable resources, lifetime/cleanup, type constraints, or concurrency timing where applicable. A successful happy path is not enough to prove the construct is used correctly.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

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