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F# / Pattern Matching

As patterns

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

10 min read • Beginner

As patterns is a focused F# lesson inside Pattern Matching. The example uses the construct named in the lesson directly rather than reusing a generic placeholder.

Trace the example from its inputs through As patterns 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-0030-90c51bdc6b.fsx
fsharp Try It Live
let values31 = [31; 32; 33]
printfn "%d" (List.sum values31) // As patterns
Edge case / engineering note

For As patterns, 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