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Specification 6.0 · Not released · Tested product 5.21.3

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    Data and patterns

    Build two ticket values and use an enum pattern to print their states.

    Prerequisite

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    Use Topaz 5.21.3 with language mode 5.21 and the SELF compiler. Complete First checked and executed program first.

    1. Build a value and handle its cases

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    Save the source as data-and-patterns.tpz. Ticket has named fields and a Status value. Construct a variant with Status.Open(). Match it with case Open().

    2. Check the program

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    Check the ticket program

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    check · checking · Verification: passed

    data-and-patterns.tpzCheck the ticket programOpen in Playground
    1. import std.io
    3. enum Status { Open, Closed }
    4. record Ticket { title: string, status: Status }
    6. function describe(ticket: Ticket) -> string {
    7. let state = match (ticket.status) {
    8. case Open() => "open"
    9. case Closed() => "closed"
    10. }
    11. return "{ticket.title}: {state}"
    12. }
    14. let first = Ticket { title: "Docs", status: Status.Open() }
    15. let second = Ticket { title: "Tests", status: Status.Closed() }
    16. io.writeLine(describe(first))
    17. io.writeLine(describe(second))
    Recorded outputexit 0
    data-and-patterns.tpz: types-ok (2 modules)
data-and-patterns.tpz: resolve-ok (2 modules)
    $ topaz check data-and-patterns.tpz --compiler self · recorded with topaz 5.21.3
    Expected result

    Expected result

    Checking accepts the program. Exit code 0.

    Observed assertions · passed · 5.21.3

    2026-11-06T13:40:33.8886819Z · checking · sha256:b6c3f574b78c558b526196fa04f5d835c9fe1df59d07397dbf4e5d279a3e1665

    Exit code 0.

    Observed stdout
    1. data-and-patterns.tpz: types-ok (2 modules)
    2. data-and-patterns.tpz: resolve-ok (2 modules)

    No stderr.

    • Passed · expected 0; observed 0
    Source evidence

    Expect exit 0. If checking fails, follow the reported diagnostic, correct the source, and check again.

    3. Run both cases

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    Print both ticket states

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    run · runtime · Verification: passed

    data-and-patterns.tpzPrint both ticket statesOpen in Playground
    1. import std.io
    3. enum Status { Open, Closed }
    4. record Ticket { title: string, status: Status }
    6. function describe(ticket: Ticket) -> string {
    7. let state = match (ticket.status) {
    8. case Open() => "open"
    9. case Closed() => "closed"
    10. }
    11. return "{ticket.title}: {state}"
    12. }
    14. let first = Ticket { title: "Docs", status: Status.Open() }
    15. let second = Ticket { title: "Tests", status: Status.Closed() }
    16. io.writeLine(describe(first))
    17. io.writeLine(describe(second))
    Recorded outputexit 0
    Docs: open
Tests: closed
    $ topaz run data-and-patterns.tpz --compiler self · recorded with topaz 5.21.3
    Expected result

    Expected result

    Execution completes. Exit code 0.

    No stderr.

    Expected stdout
    1. Docs: open
    2. Tests: closed
    Observed assertions · passed · 5.21.3

    2026-11-06T13:40:33.9748471Z · runtime · sha256:b6c3f574b78c558b526196fa04f5d835c9fe1df59d07397dbf4e5d279a3e1665

    Exit code 0.

    Observed stdout
    1. Docs: open
    2. Tests: closed

    No stderr.

    • Passed · expected 0; observed 0
    • Passed · stdout matches the authored expectation
    • Passed · stderr matches the authored expectation
    Source evidence

    The two calls exercise both cases used by describe.

    Verification

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    Public Topaz 5.21.3 checked and ran this program successfully in Docs run 42224592687, attempt 2. The recorded exit codes and output were compared with this page's current product assertions. The fixture files, invocation and expected output were unchanged.

    Records, enums and newtypes defines the declarations used here. Pattern matching defines variant patterns, case selection and match coverage.

    Next steps

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    Functions and generics

    check

    std.io.writeLine

    Continue with Generic functions and protocols. For parameter and return syntax, use Functions and generics.

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