macro fn(n, ex)
    func = ex.args[1]
    res = ex
    for i in 1:(n - 1)
        res = Expr(:call, func, res)
    end

    return quote
        $(esc(res))
    end
end

f(x) = 2x

@fn 10 f(5) # 5120

 @macroexpand @fn 10 f(5)
quote
    f(f(f(f(f(f(f(f(f(f(5))))))))))
end

@fn 1000 sin(1)
0.05459297151018517

@fn 10_000 sin(1)
ERROR: syntax: invalid syntax (memory-error out of gc handles)
Stacktrace:
 [1] top-level scope at none:0

@btime @fn 1000 sin(1)
  9.495 μs (0 allocations: 0 bytes)

@btime let res
    cnt = 0
    for outer res in iterated(sin, 1)
        cnt == 1000 && break
        cnt += 1
    end
end