Q1, you're assuming you can design upfront; that is, that you understand the problem, you have enough information to solve the problem, the world won't change and so on.
Q2, the ceremony of types itself has a cost. You have to think about it, type it - and you may need to change it. When types ripple through layers of calls, the changes do too.
Note: I don't know the answer. I notice that dynamic languages seem to be becoming more popular (are they? or are they just more publicized?) In a rapidly changing world, it's more important to adapt now than perfect. There's a general trend, that because computers get faster but humans don't, more and more of the work will be transfered to the computer. Dynamic languages do this in the sense that they are less efficient than static languages - on the assumption that speed is the main benefit of static languages. Certainly, the coder has less work to do. Another benefit is that it makes coding accessible to less skilled people (and more skilled people who have less time to devote to a particular task).
There are trade-offs. The first thing is to note what the trade-offs are. The second thing is to note what groups of people use programming languages and for what tasks. The third thing is to ask how those people value those trade-offs, for those specific tasks. e.g. Perhaps sometimes, a crappy, hard-to-maintain, only partially correct solution now is better than a high-quality, clear, correct solution too late?
Q2, the ceremony of types itself has a cost. You have to think about it, type it - and you may need to change it. When types ripple through layers of calls, the changes do too.
Note: I don't know the answer. I notice that dynamic languages seem to be becoming more popular (are they? or are they just more publicized?) In a rapidly changing world, it's more important to adapt now than perfect. There's a general trend, that because computers get faster but humans don't, more and more of the work will be transfered to the computer. Dynamic languages do this in the sense that they are less efficient than static languages - on the assumption that speed is the main benefit of static languages. Certainly, the coder has less work to do. Another benefit is that it makes coding accessible to less skilled people (and more skilled people who have less time to devote to a particular task).
There are trade-offs. The first thing is to note what the trade-offs are. The second thing is to note what groups of people use programming languages and for what tasks. The third thing is to ask how those people value those trade-offs, for those specific tasks. e.g. Perhaps sometimes, a crappy, hard-to-maintain, only partially correct solution now is better than a high-quality, clear, correct solution too late?