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Result and option

Why errors are values, and when match is required.

Errors as data

Abort is for the impossible. Recoverable failure is data the caller must see. ! packages that failure as a result err. Required match keeps the bad path visible at compile time, matching the discipline used for option some/none arms.

Result

! returns an error payload from the current function and leaves the process running. Any ! in a body makes that function a result: ^ v is ok, ! e is err.

/ std/io
/ std/str

$ checked = (x) {
    ? x < 0 {
        ! 99
    }
    ^ x
}

| checked(7) {
    $ v {
        io.print(str.from_int(v))
    }
    ! e {
        io.print(str.from_int(e))
        ^ 1
    }
}

Option

Option-shaped functions use ^ value for some and bare ^ for none. Match with $ name {…} and : {…}.

Must handle

Leaving a result or option unhandled is a compile error. There is no silent discard and no separate “try” keyword.