[LUAU] doing 'e'

[Jim Thompson]

damn, now we just need an erlang implementation.
http://www.erlang.org/course/course.html

(funny that nobody stepped to the plate with perl)

Tim Newsham wrote:

> Here it is in haskell.  This shows some of the strengths of
> haskell, but also some of its weaknesses.  Dealing with random
> numbers is more tedious than it should be.  Some of the awkwardness
> could be caused by the programmer's lack of experience with the
> language.
>
> ----- e.lhs -----
> Literate haskell for computing "e" the hard way. Translated from lisp 
> code by Jim Thompson (see e.lisp)
>
>> module E where
>> import Time
>> import System.Random
>
>
> Some siliness so that the random numbers are different for each run.
>
>> randomSeed :: IO Int
>> randomSeed = do                       -- XXX Could be a lot better.
>>       t <- getClockTime >>= toCalendarTime
>>       return $ hashStr $ show t where
>>               hashStr s = foldl hashAdd 0 $ map fromEnum s
>>               hashAdd a b = (a*13) + b
>
>
> A sum is the accumulation from 0.  We call it sum' because there's 
> already
> an integer sum function.  A list of accumulated sums is made by 
> keeping each intermediate sum value.
>
>> sum' = foldl (+) 0.0
>> sums = scanl (+) 0.0
>
>
> Average of a list is its sum divided by its length.
>
>> average x = sum' (map fromIntegral x) / (fromIntegral $ length x)
>
>
> length of series items whose sum does not exceed 1.0.
>
>> waitTime x = length $ takeWhile (< 1.0) (sums x)
>
>
> A number of waitTimes drawn from successive items in x.
>
>> waitTimes x 0 = []
>> waitTimes x n = let wt = waitTime x in             wt : waitTimes 
>> (drop wt x) (n - 1)
>
>
>> putLine x = putStr $ (show x) ++ "\n"
>
>
>> main :: IO ()
>> main = do
>>       seed <- randomSeed
>>       let variates = randoms $ mkStdGen seed
>>       mapM_ putLine $ [average $ waitTimes variates n | n <- 
>> [1,10,100,1000]]
>
>
> Tim Newsham
> http://www.lava.net/~newsham/
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