haskell framework code for neural nets PA4 Q10

import Prelude hiding (id, (.))
import Control.Arrow
import Control.Applicative
import Control.Category
import Control.Monad
import Control.Monad.Trans.Class

import System.Environment

import Text.CSV
import Text.Printf


pfcn_slow :: [[Double]] -> Double
pfcn_slow wts = log $ sum [assn_value h v | h <- hiddens, v <- visibles] where
    -- value of an assignment to hidden and visible units
    assn_value :: [Double] -> [Double] -> Double
    assn_value hs vs = exp $ sum [h_i * wts_ij * v_j
        | (h_i, wts_i) <- zip hs wts
        , (v_j, wts_ij) <- zip vs wts_i]

    -- all assignments to hidden and visible variables
    hiddens, visibles :: [[Double]]
    hiddens = assns (length wts)
    visibles = assns (length (head wts))

assns :: Int -> [[Double]]
assns 0 = [[]]
assns n = (map (0:) (assns $ n-1)) ++ (map (1:) (assns $ n-1))

-- given (log x_i), compute log (sum_i x_i) in a numerically stable manner
logs_to_logsum :: [Double] -> Double
logs_to_logsum logxs
    | log_max_xs <- maximum logxs
    = log_max_xs + log (sum [exp (logx - log_max_xs) | logx <- logxs])

prod_over :: [α] -> (α -> Double) -> Double
prod_over xs = product . flip map xs

-- log (\prod_i f(i))
-- which, of course, equals \sum_i log f(i), I just like the conceptual name
log_prod_over :: [α] -> (α -> Double) -> Double
log_prod_over xs = sum . flip map xs . (log .)

should_be_eq = (exp $ log_prod_over [1, 2, 3, 4] id, 24)

logsumover :: [α] -> (α -> Double) -> Double
-- given some indices {i}, and a function yielding {log f(i)},
-- compute log (sum_i f(i))
logsumover indices i_to_logx = logs_to_logsum (map i_to_logx indices)

should_be_eq' = (exp $ logsumover [1, 2, 3] log, 6)

pfcn_fast :: [[Double]] -> Double
pfcn_fast wts = YOUR IMPLEMENTATION HERE

main = go =<< parseCSVFromFile . head =<< getArgs where
    go (Left err) = print "couldn't parse CSV; usage: rbm_part_fcn csv_file"
    go (Right csv) = print $ pfcn_fast (map (map read) $ stripNewline csv)
    stripNewline csv
        | last csv == [""] = init csv
        | otherwise = csv