Pointer Arithmetic

peano.zig

const std = @import("std");

fn Add(comptime A: type, comptime B: type) type {
    if (A == type) {
        return B;
    } else {
        return Add(@typeInfo(A).Pointer.child, *B);
    }
}

fn Fib(comptime N: type) type {
    return switch (N) {
        type => type,
        *type => *type,
        else => Add(Fib(@typeInfo(N).Pointer.child), Fib(@typeInfo(@typeInfo(N).Pointer.child).Pointer.child)),
    };
}

fn Seq(comptime N: type) [toInt(N)]type {
    if (N == type) {
        return [_]type{};
    } else {
        return Seq(@typeInfo(N).Pointer.child) ++ [_]type{N};
    }
}

fn toInt(comptime N: type) comptime_int {
    if (N == type) {
        return 0;
    } else {
        return 1 + toInt(@typeInfo(N).Pointer.child);
    }
}

pub fn main() !void {
    var buf: [4]u8 = undefined;
    const stdout = try std.io.getStdOut();
    inline for (Seq(*************type)) |N| {
        try stdout.write(try std.fmt.bufPrint(buf[0..], "{}\n", u8(toInt(Fib(N)))));
    }
}