module CSVReader where
-- Based on notes http://web.cecs.pdx.edu/~sheard/course/CyberMil/Notes/monads.pptx
import Control.Monad.State
import CSV
--------------------------------------------
-- Try 1
getString:: [String] -> (String,[String])
getString (s:ss) = (s,ss)
getString [] = error "No more strings to read a 'String' from"
getInt:: [String] -> (Int,[String])
getInt (s:ss) = (read s,ss)
getInt [] = error "No more strings to read an 'Int' from"
getInts:: Int -> [String] -> ([Int],[String])
getInts 0 ss = ([],ss)
getInts n ss = case getInt ss of
 (x,ss2) -> case getInts (n-1) ss2 of
 (xs,ss3) -> (x:xs,ss3)
 
getLine6:: [String] -> ((String,[Int]),[String])
getLine6 ss = case getString ss of
 (count,ss2) -> case getInts 3 ss2 of
 (rolls,ss3) -> ((count,rolls),ss3)
--------------------------------------------
-- Try 2.
-- Use a monad
-- Define a function for each type
-- Separate reading a line from reading a file.
-- data State s a = State (s -> (a,s))
type Line a = State [String] a
bool:: Line Bool
bool = (state f)
 where f ("True" : ss) = (True,ss)
 f ("False" : ss) = (False,ss)
 f (x:xs) = error ("Non Bool in reader bool: "++x)
 f [] = error "No more strings to read a 'Bool' from"
string:: Line String
string = state f
 where f (s:ss) = (s,ss)
 f [] = error "No more strings to read a 'String' from"
 
int:: Line Int
int = mapState f (return ())
 where f ((),s:ss) = (read s,ss)
 f ((),[]) = error "No more strings to read an 'Int' from"
 
skip:: Line ()
skip = state f
 where f (s:ss) = ( (), ss)
 f [] = error "No more strings to 'skip' over"
list:: Int -> Line a -> Line [a]
list 0 r = return []
list n r = do { x <- r; xs <- list (n-1) r; return(x:xs)} blank:: Line a -> Line(Maybe a)
blank m = state f 
 where f ("":xs) = (Nothing, xs)
 f xs = case (runState m) xs of
 (y,ys) -> (Just y,ys)
--------------------------------------------
-- Use these to build readers for a whole line
getLine1 :: Line [String]
getLine1 =
 do { skip
 ; list 3 string
 }
 
getLine2_18 :: Line (String,[Maybe Int])
getLine2_18 = 
 do { count <- string ; rolls <- list 3 (blank int) ; return(count,rolls) } ------------------------------------------- -- Reading a whole file of Comma Separated Values -- which is represented by [[String]] type Reader a = State [[String]] a lineToReader:: Line a -> Reader a
lineToReader l1 = mapState f (return ())
 where f ((),line:lines) = (evalState l1 line,lines)
getN :: Int -> Line a -> Reader [a]
getN 0 line = return []
getN n line =
 do { x <- lineToReader line ; xs <- getN (n-1) line ; return(x:xs) } importCSV :: Reader a -> String -> IO a
importCSV reader file = 
 do { r <- parseCSVFromFile file; (f r)} where f (Left err) = error ("Error reading from file: "++ file++"\n"++show err) f (Right xs) = return(evalState reader xs) -------------------------------------------------- -- Put it all together for a first test get3DieExample :: Reader ([String],[(String,[Maybe Int])]) get3DieExample = do { labels <- lineToReader getLine1 ; pairs <- getN 18 getLine2_18 ; return(labels,pairs) } test1 = importCSV get3DieExample "roll3Die.csv" -------------------------------------------- -- Generic Monad operations infixr 3 `x` x :: Monad m => m b -> m c -> m(b,c) 
r1 `x` r2 = do { a <- r1; b <- r2; return(a,b) } many :: Monad m => Int -> m c -> m [c]
many n r = sequence (replicate n r)
 where -- sequence is in the Prelude but we provide
 -- a definition here because it is interesting
 sequence [] = return []
 sequence (c:cs) = do { x <- c ; xs <- sequence cs ; return(x:xs)} row:: (a -> b) -> Line a -> Reader b
row f line1 = lineToReader line2
 where line2 = do { x <- line1; return(f x) }
get3DieEx2 = 
 (row snd (skip `x` list 3 string)) 
 `x` (many 18 (row id (string `x` list 4 (blank int))))
test2 = importCSV get3DieEx2 "roll3Die.csv" 
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