module CSVReader3 where
import Control.Monad.State
import CSV
--------------------------------------------------
-- Line and Table Readers with position tracking
type Line a = State (Int,Int,[String]) a
type Table a = State (Int,[[String]]) a
report l c message =
 error ("\n at line: "++show l++", column: "++show c++"\n "++message)
 
tab:: Line a -> Table a
tab m = (state g) 
 where g (l,line:table) = let (x,(lin,col,extra)) = runState m (l,0,line)
 in (x,(l+1,table))
------------------------------------------------------------
-- How to read particular types
bool:: Line Bool
bool = (state f)
 where f (l,c,"True" : ss) = (True,(l,c+1,ss))
 f (l,c,"False" : ss) = (False,(l,c+1,ss))
 f (l,c,x:xs) = report l c ("Non Bool in reader bool: "++x)
 f (l,c,[]) = report l c "No more strings to read a 'Bool' from"
string:: Line String
string = state f
 where f (l,c,s:ss) = (s,(l,c+1,ss))
 f (l,c,[]) = report l c "No more strings to read a 'String' from"
 
int:: Line Int
int = mapState f (return ())
 where f ((),(l,c,s:ss)) = (read s,(l,c+1,ss))
 f ((),(l,c,[])) = report l c "No more strings to read an 'Int' from"
 
skip:: Line ()
skip = state f
 where f (l,c,s:ss) = ( (), (l,c+1,ss))
 f (l,c,[]) = report l c "No more strings to 'skip' over"
blank:: Line a -> Line(Maybe a)
blank m = state f 
 where f (l,c,"":xs) = (Nothing, (l,c+1,xs))
 f xs = case runState m xs of
 (y,ys) -> (Just y,ys)
------------------------------------------------------------
-- generic operators for any monad
infixl 3 `x`
infixl 3 `x2`
infixl 3 `x3`
infixl 3 `x4`
infixl 3 `bind`
bind x f = do { a <- x; b <- f a; return(a,b)} r1 `x` x = do { a <- r1; b <- x; return(a,b) } pair `x2` x = do { (a,b) <- pair; c <- x; return(a,b,c)} trip `x3` x = do { (a,b,c) <- trip; d <- x; return(a,b,c,d)} quad `x4` x = do { (a,b,c,d) <- quad; e <- x; return(a,b,c,d,e)} list:: Monad m => m a -> Int -> m [a]
list r 0 = return []
list r n = do { x <- r; xs <- list r (n-1); return(x:xs)} ------------------------------------------------- -- an example reader ww = tab (skip>> list string 3) `x`
 list (tab (int `x` list (blank int) 3)) 18 `x2`
 tab (int `bind` list bool)
 
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