011 selected variant carries effect arm

// Pins that a SELECTED proc variant on an effect-bearing tor receives the
// caller's effect arms.
//
// The twin of 370_010, which pins the UNSELECTED side. A variant handler is a
// standalone function, not an inline splice, so it only sees `tick` if it takes
// the same `comptime __H: type` parameter the bare handler takes and binds the
// same aliases. Here `|alt` is the registered variant, so the arm must fire
// from inside it and reach the caller's continuation.
//
// `$mod.factor` also rides the selected path, so the module rewrite is pinned
// on both sides.

~import std/io
~import std/build

const std = @import("std");
const factor: i32 = 10;

~tor pump { n: i32 }
! tick i32
| done string

~proc pump|zig {
    tick(n * $mod.factor);
    return .{ .done = "zig" };
}

~proc pump|alt {
    tick(n * $mod.factor * 2);
    return .{ .done = "alt" };
}

~std/build:variants {
    "input:pump": "alt"
}
| configured _ |> _
| skipped _ |> _
| invalid-event _ |> _

~tor show { value: i32 }

~proc show|zig {
    std.debug.print("{}\n", .{value});
}

~tor drive { n: i32 }
| finished string
| blank

~drive =
    pump(n)
    ! tick t |> show(value: t)
    | done d -> finished d

~drive(n: 3)
| finished f |> std/io:print.ln(f)
| blank |> std/io:print.ln("blank")