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Re: Mathematica daily WTF (programming everything functionally?)

On 1/3/2011 12:57 AM, Andrzej Kozlowski wrote:
> In any case, I cannot think of any scientific or mathematical problems that
  can be more naturally formulated in terms of "side-effects" than in terms
of "functions". Perhaps they exist and I my bias is due to several decades
of doing mathematics but I seriously can't think of a single example.
Can you provide one?

Surely this argument has been expressed by proponents of purely 
functional programming languages, for which they have provided
mechanisms to get over the difficulties.

OK, here is a problem:
simulate a stock market, where you have 1000 stocks with prices.
Every time step your program surveys 100,000 traders who wish
to buy or sell some number of shares of one of the stocks at
some price.  When you find a match, namely compatible sell/buy
price and compatible number of shares, update the ownership of
the 100,000 traders to reflect the transaction. Do this forever,
periodically taking a snapshot/ backup of the situation, and
logging all transactions as they occur.

I think AES had other examples in mind, simulating dynamical systems
or something.

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