Inline....
On 14/01/2009 01:08, "Luke Palmer" <lrpal...@gmail.com> wrote: > On Tue, Jan 13, 2009 at 5:45 PM, Phil <pbeadl...@mail2web.com> wrote: >> mcSimulate :: Double -> Double -> Word64 -> [Dou >> ble] >> mcSimulate startStock endTime seedForSeed = fst expiryStock : mcSimulate >> startStock endTime newSeedForSeed >> >> It is abundantly clear that the startStock and endTime are just being passed >> around from call to call unchanged that is their value is constant >> throughout the the simulation. For the purposes here when I'm only passing 2 >> 'constants' around it doesn't strike me as too odd, but my list of >> 'constants' is likely to grow as I bolt more functionality onto this. For >> readability, I understand that I can create new types to encapsulate complex >> data types into a single type , but I can't help thinking that passing say 9 >> or 10 'constants' around and around like this 'feels wrong'. If I sit back >> and think about it, it doesn't strike me as implausible that the compiler >> will recognize what I'm doing and optimize this out for me, and what I'm >> doing is thinking about the whole think like a C++ programmer (which I >> traditionally am) would. > > You can factor out constants in a couple ways. If you are just passing > constants between a recursive call to the same function, you can factor out > the recursive bit into a separate function: > > something param1 param2 = go > where > go = ... param1 ... param2 ... etc ... go ... > etc = ... > > Where go takes only the parameters that change, and the rest is handled by its > enclosing scope. You might buy a little performance this way too, depending > on the compiler's cleverness (I'm not sure how it optimizes these things). > > > [PHIL] > Firstly thanks for your advice. > > When I say constants, I should be clear these are parameters passed in by > the user, but they remain constant throughout the recursive call. I think the > example above is only relevant if they are constants at compile time? If not > I¹m not sure I follow the example. If we have something like > > mcSimulate :: Double -> Double -> Word64 -> [Double] > mcSimulate startStock endTime seedForSeed = fst expiryStock : mcSimulate > startStock endTime newSeedForSeed > where > expiryStock = iterate evolveUnderlying (startStock, ranq1Init seedForSeed) > !! truncate (endTime/timeStep) > newSeedForSeed = seedForSeed + 246524 > > Here startStock and endTime are not altered from iteration to iteration, but > they are not known at compile time. I see that I can reduce this to something > like > > test seedForSeed = fst expiryStock : test newSeedForSeed > where > expiryStock = iterate evolveUnderlying (_startStock, ranq1Init > seedForSeed) !! truncate (_endTime/timeStep) > newSeedForSeed = seedForSeed + 246524 > > But don¹t understand how I feed¹ the _startStock and _endTime in? > > Could you explain this in detail, or confirm my suspicions that it only works > for compile-time constants? > > > Thanks again, > > Phil.
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