sb.hs

import Data.Ratio
loop x a = do
    print a
    let (l,r) = sb a
    let (_,(d,e)) = l
    case compare (fromRational (d%e)) x of
        EQ -> return $ d%e
        GT -> loop x l
        LT -> loop x r
sb((x,y),(z,w))=(a,b)
    where   a = ((x,y),c)
            b= (c,(z,w))
            c= (z+x,y+w)
main = do
    let a = (0,1)
    let b = (1,0)
    let r = (a,b)
    loop pi r >>= print