170 fold prefix drops effect handlers

✓ Passing This code compiles and runs correctly.

Code

// PINS: a fold preceded by a prefix bind must still thread the effect-branch
// Handlers type into the folded event.
//
// An event carrying `!` arms compiles to a handler taking TWO parameters —
// the input and the comptime Handlers type that holds the arm bodies:
//
//     pub fn handler(__koru_event_input: Input, comptime __H: type) Output
//
// With a prefix ahead of the fold head, both the fold's seed call and its
// back-edge re-invocation are emitted with the input alone, and the arity
// mismatch surfaces as a raw Zig error naming a `__H` the author never wrote.
//
// The isolation, one variable at a time:
//   `#loop step(n: 0)` + effect arms                  — composes
//   two effect arms, no prefix                        — composes
//   `seed(): n0 |> #loop step(n: n0)` + effect arms   — this pin
//
// So the fault is the prefix position, the same one 210_166 holds, and a
// DIFFERENT fault there: 210_166 is the exit arm's capture, this is Handlers
// threading. Two defects living at one syntactic position, which is why each
// gets its own pin rather than one test varying both.
//
// Why it matters beyond the grammar: this shape IS a blocking `await` — pump a
// pending operation in a fold, firing progress/completion arms each round,
// until it drains. The non-fold spelling of the same design already composes.
~import std/io

~tor seed {} -> i32
~proc seed|zig { return 0; }

~tor step { n: i32 }
! tick i32
| again i32
| stop i32

~proc step|zig {
    tick(n);
    if (n < 3) return .{ .again = n + 1 };
    return .{ .stop = n };
}

~tor spin {} -> i32

~spin = seed(): n0 |> #loop step(n: n0)
! tick t |> std/io:print.ln("  tick {{ t:d }}")
| again v |> @loop(n: v)
| stop r -> r

~spin(): f |> std/io:print.ln("done {{ f:d }}")

input.kz

Supporting Files

UnsupportedConstruct

CS_REFUSES

~proc seed|cs { return 0; 
}
~proc step|cs {
    tick(n);
    if (n < 3) return new Output { tag = "again", again = n + 1 };
    return new Output { tag = "stop", stop = n };
}

input.kcs

Actual · Zig

✓ pass

  tick 0
  tick 1
  tick 2
  tick 3
done 3

Actual · C#

✗ UnsupportedConstruct

Expected output

✓ Zig✗ C#

  tick 0
  tick 1
  tick 2
  tick 3
done 3

Emitted Zig source

// Access compiler flags via the per-user compiler_env module
const CompilerEnv = @import("compiler_env").CompilerEnv;

pub const panic = if (@import("builtin").mode == .Debug)
    @import("std").debug.FullPanic(@import("std").debug.defaultPanic)
else
    @import("std").debug.simple_panic;


const __koru_bare = struct {
    extern fn posix_memalign(memptr: *?*anyopaque, alignment: usize, size: usize) c_int;
    extern fn free(ptr: ?*anyopaque) void;
    fn bareAlloc(_: *anyopaque, len: usize, alignment: @import("std").mem.Alignment, _: usize) ?[*]u8 {
        var p: ?*anyopaque = null;
        const a = @max(alignment.toByteUnits(), @sizeOf(usize));
        if (posix_memalign(&p, a, len) != 0) return null;
        return @ptrCast(p);
    }
    fn bareResize(_: *anyopaque, _: []u8, _: @import("std").mem.Alignment, _: usize, _: usize) bool { return false; }
    fn bareRemap(_: *anyopaque, _: []u8, _: @import("std").mem.Alignment, _: usize, _: usize) ?[*]u8 { return null; }
    fn bareFree(_: *anyopaque, memory: []u8, _: @import("std").mem.Alignment, _: usize) void { free(@ptrCast(memory.ptr)); }
    const vtable = @import("std").mem.Allocator.VTable{ .alloc = bareAlloc, .resize = bareResize, .remap = bareRemap, .free = bareFree };
    const allocator = @import("std").mem.Allocator{ .ptr = undefined, .vtable = &vtable };
};
const __koru_backing = if (@import("builtin").link_libc) @import("std").heap.c_allocator else if (@import("builtin").os.tag == .freestanding and !@import("builtin").cpu.arch.isWasm()) __koru_bare.allocator else @import("std").heap.page_allocator;
var __koru_leak_count: @import("std").atomic.Value(usize) = .init(0);
var __koru_par_tasks: @import("std").atomic.Value(usize) = .init(0);
const __koru_par_CAP: usize = 128;
threadlocal var __koru_par_depth: usize = 0;
const __koru_par_DEPTH_CAP: usize = 7;
var __koru_par_pool: @import("std").Thread.Pool = undefined;
var __koru_par_pool_ready: bool = false;
var __koru_par_pool_mtx: @import("std").Thread.Mutex = .{};
fn __koru_par_pool_ensure() *@import("std").Thread.Pool {
    __koru_par_pool_mtx.lock();
    defer __koru_par_pool_mtx.unlock();
    if (!__koru_par_pool_ready) {
        @import("std").Thread.Pool.init(&__koru_par_pool, .{ .allocator = @import("std").heap.smp_allocator }) catch @panic("koru: thread pool init failed");
        __koru_par_pool_ready = true;
    }
    return &__koru_par_pool;
}
fn __koru_alloc(ctx: *anyopaque, len: usize, alignment: @import("std").mem.Alignment, ret_addr: usize) ?[*]u8 {
    _ = ctx;
    const r = __koru_backing.rawAlloc(len, alignment, ret_addr);
    if (comptime @import("builtin").mode == .Debug) {
        if (r != null) _ = __koru_leak_count.fetchAdd(1, .monotonic);
    }
    return r;
}
fn __koru_resize(ctx: *anyopaque, memory: []u8, alignment: @import("std").mem.Alignment, new_len: usize, ret_addr: usize) bool {
    _ = ctx;
    return __koru_backing.rawResize(memory, alignment, new_len, ret_addr);
}
fn __koru_remap(ctx: *anyopaque, memory: []u8, alignment: @import("std").mem.Alignment, new_len: usize, ret_addr: usize) ?[*]u8 {
    _ = ctx;
    return __koru_backing.rawRemap(memory, alignment, new_len, ret_addr);
}
fn __koru_free(ctx: *anyopaque, memory: []u8, alignment: @import("std").mem.Alignment, ret_addr: usize) void {
    _ = ctx;
    __koru_backing.rawFree(memory, alignment, ret_addr);
    if (comptime @import("builtin").mode == .Debug) {
        _ = __koru_leak_count.fetchSub(1, .monotonic);
    }
}
const __koru_vtable = @import("std").mem.Allocator.VTable{ .alloc = __koru_alloc, .resize = __koru_resize, .remap = __koru_remap, .free = __koru_free };
pub fn koru_allocator() @import("std").mem.Allocator {
    return .{ .ptr = undefined, .vtable = &__koru_vtable };
}

pub inline fn __koru_intcast(comptime T: type, x: anytype) T {
    if (comptime (@import("builtin").mode == .Debug or @import("builtin").mode == .ReleaseSafe))
        return @as(T, @intCast(x));
    const dst = @typeInfo(T);
    const src = @typeInfo(@TypeOf(x));
    if (comptime (dst == .int and src == .int and dst.int.bits == src.int.bits and dst.int.signedness != src.int.signedness))
        return @as(T, @bitCast(x));
    return @as(T, @intCast(x));
}

fn __KoruPadI(comptime T: type) type {
    const V = switch (@typeInfo(T)) { .comptime_int => i64, .comptime_float => f64, else => T };
    return struct {
        v: V,
        width: usize,
        pub fn format(self: @This(), w: *@import("std").Io.Writer) @import("std").Io.Writer.Error!void {
            const rendered = @import("std").fmt.count("{d}", .{self.v});
            const pad = self.width -| rendered;
            for (0..pad) |_| try w.writeByte(' ');
            try w.print("{d}", .{self.v});
        }
    };
}
pub fn __koru_pad_i(width: usize, value: anytype) __KoruPadI(@TypeOf(value)) {
    return .{ .v = value, .width = width };
}

pub fn koru_leak_check() void {
    if (comptime @import("builtin").mode != .Debug) return;
    if (__koru_leak_count.load(.acquire) == 0) return;
    if (comptime @import("builtin").target.os.tag == .freestanding) {
        if (comptime @import("builtin").cpu.arch == .wasm32 or @import("builtin").cpu.arch == .wasm64) {
            @panic("KORU LEAK CHECK FAILED: the produced program leaked");
        } else {
            const __klc = struct { extern var stdout: ?*anyopaque; extern fn fputs(__s: [*:0]const u8, __st: ?*anyopaque) c_int; };
            var __lb: [128]u8 = undefined;
            const __lm = "KORU LEAK CHECK FAILED: allocations still outstanding at end of run: ";
            @memcpy(__lb[0..__lm.len], __lm);
            var __ln: usize = __lm.len;
            var __lv = __koru_leak_count.load(.acquire);
            var __ld: [20]u8 = undefined;
            var __lk: usize = 0;
            while (__lv > 0) : (__lk += 1) { __ld[__lk] = @intCast('0' + __lv % 10); __lv /= 10; }
            for (0..__lk) |__li| { __lb[__ln] = __ld[__lk - 1 - __li]; __ln += 1; }
            __lb[__ln] = '\n'; __ln += 1; __lb[__ln] = 0;
            _ = __klc.fputs(@as([*:0]const u8, @ptrCast(&__lb)), __klc.stdout);
            @trap();
        }
    } else {
        @import("std").debug.print("KORU LEAK CHECK FAILED: the produced program leaked (trace above)\n", .{});
        @import("std").process.exit(1);
    }
}

pub const main_module = struct {
    pub const seed_event = struct {
        pub const Input = struct {
        };
        pub const Output = i32;
        pub fn handler(__koru_event_input: @This().Input) @This().Output {
            // >>> PROC: seed  [tests/regression/200_COMPILER_FEATURES/210_PARSER/210_170_fold_prefix_drops_effect_handlers/input.kz:30]
            _ = &__koru_event_input;
            return 0;

        }
    };
    pub const step_event = struct {
        pub const Input = struct {
            n: i32,
        };
        pub const Output = union(enum(u8)) {
            again: i32,
            stop: i32,
        };
        pub fn handler(__koru_event_input: @This().Input, comptime __H: type) @This().Output {
            const tick = __H.tick;
            _ = &tick;
            // >>> PROC: step  [tests/regression/200_COMPILER_FEATURES/210_PARSER/210_170_fold_prefix_drops_effect_handlers/input.kz:37]
            const n = __koru_event_input.n;
            _ = &n;
            _ = &__koru_event_input;

                tick(n);
                if (n < 3) return .{ .again = n + 1 };
                return .{ .stop = n };

        }
    };
    pub const spin_event = struct {
        pub const Input = struct {
        };
        pub const Output = i32;
        pub fn handler(__koru_event_input: @This().Input) @This().Output {
            // >>> SUBFLOW: tests/regression/200_COMPILER_FEATURES/210_PARSER/210_170_fold_prefix_drops_effect_handlers/input.kz:45
            _ = &__koru_event_input;
            const result = main_module.seed_event.handler(.{ });
            const n0 = result;
            _ = &result;
var loop_n: i32 = n0;
const Handlers_0 = struct {
    fn tick(t: i32) void {
        _ = &t;
        {
            (struct { fn __kout(__fd: i32, __b: []const u8) void { if (@import("builtin").os.tag == .freestanding) { const __kc = struct { extern var stdout: ?*anyopaque; extern var stderr: ?*anyopaque; extern fn fputs(__s: [*:0]const u8, __st: ?*anyopaque) c_int; }; var __kt: [4096]u8 = undefined; for (0..(__b.len + __kt.len - 2) / (__kt.len - 1)) |__ki| { const __kn = @min(__kt.len - 1, __b.len - __ki * (__kt.len - 1)); @memcpy(__kt[0..__kn], __b[__ki * (__kt.len - 1)..][0..__kn]); __kt[__kn] = 0; @import("std").mem.doNotOptimizeAway(__kc.fputs(@as([*:0]const u8, @ptrCast(&__kt)), if (__fd == 2) __kc.stderr else __kc.stdout)); } } else { @import("std").mem.doNotOptimizeAway(@import("std").posix.write(__fd, __b) catch @as(usize, 0)); } } fn __kw(comptime __f: []const u8, __a: anytype) void { var __kb: [65536]u8 = undefined; const __ks = @import("std").fmt.bufPrint(&__kb, __f, __a) catch __kb[0..0]; __kout(1, __ks); } }).__kw("  tick {d}\n", .{t});
        }
    }
};
loop: while (true) {
    const result_0 = main_module.step_event.handler(.{ .n = loop_n }, Handlers_0);
    switch (result_0) {
        // >>> BRANCH: tests/regression/200_COMPILER_FEATURES/210_PARSER/210_170_fold_prefix_drops_effect_handlers/input.kz:48  | stop r |>
        .stop => |r| {
            return r;
        },
        // >>> BRANCH: tests/regression/200_COMPILER_FEATURES/210_PARSER/210_170_fold_prefix_drops_effect_handlers/input.kz:47  | again v |>
        .again => |v| {
            loop_n = v;
            continue :loop;
        },
    }
    break :loop;
}
@panic("koru: a #label fold arm in 'spin' exited the loop without a continue or a `->` produce — the handler owes a value it never made");
        }
    };
    // >>> FLOW: tests/regression/200_COMPILER_FEATURES/210_PARSER/210_170_fold_prefix_drops_effect_handlers/input.kz:50  ~input:spin()
    pub fn flow0() void {
        const f = main_module.spin_event.handler(.{  });
        (struct { fn __kout(__fd: i32, __b: []const u8) void { if (@import("builtin").os.tag == .freestanding) { const __kc = struct { extern var stdout: ?*anyopaque; extern var stderr: ?*anyopaque; extern fn fputs(__s: [*:0]const u8, __st: ?*anyopaque) c_int; }; var __kt: [4096]u8 = undefined; for (0..(__b.len + __kt.len - 2) / (__kt.len - 1)) |__ki| { const __kn = @min(__kt.len - 1, __b.len - __ki * (__kt.len - 1)); @memcpy(__kt[0..__kn], __b[__ki * (__kt.len - 1)..][0..__kn]); __kt[__kn] = 0; @import("std").mem.doNotOptimizeAway(__kc.fputs(@as([*:0]const u8, @ptrCast(&__kt)), if (__fd == 2) __kc.stderr else __kc.stdout)); } } else { @import("std").mem.doNotOptimizeAway(@import("std").posix.write(__fd, __b) catch @as(usize, 0)); } } fn __kw(comptime __f: []const u8, __a: anytype) void { var __kb: [65536]u8 = undefined; const __ks = @import("std").fmt.bufPrint(&__kb, __f, __a) catch __kb[0..0]; __kout(1, __ks); } }).__kw("done {d}\n", .{f});
    }
    pub fn koru_start_flow() void {
        const result_0 = koru_koru.start_event.handler(.{  });
        const result_0_done = result_0.done;
        _ = &result_0_done;
    }
    pub fn koru_end_flow() void {
        const result_0 = koru_koru.end_event.handler(.{  });
        const result_0_done = result_0.done;
        _ = &result_0_done;
    }
};

pub const koru_koru = struct {
    pub const start_event = struct {
        pub const Input = struct {
        };
        pub const Output = union(enum(u8)) {
            done: struct {
            },
        };
        pub fn handler(__koru_event_input: @This().Input) @This().Output {
            _ = &__koru_event_input;
            return .{ .done = .{} };
        }
    };
    pub const end_event = struct {
        pub const Input = struct {
        };
        pub const Output = union(enum(u8)) {
            done: struct {
            },
        };
        pub fn handler(__koru_event_input: @This().Input) @This().Output {
            _ = &__koru_event_input;
            return .{ .done = .{} };
        }
    };
};
pub fn main() void {
    main_module.koru_start_flow();
    main_module.flow0();
    main_module.koru_end_flow();
    if (comptime @import("builtin").mode == .Debug) koru_leak_check();
}

test {
    @import("std").testing.refAllDeclsRecursive(@This());
}

Flows

subflow ~spin click a branch to expand · @labels scroll to their anchor

seed

flow ~spin click a branch to expand · @labels scroll to their anchor

spin

Test Configuration

MUST_RUN LANGUAGES: zig cs

← 169 chain after multiline source block on definition line 171 double slash in midchain string →