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{- This uses lazy evaluation to define Pascals triangle -}
module Main where
pascal :: [[Int]]
pascal = [1] : [[x+y | (x,y) <- zip ([0]++r) (r++[0])] | r <- pascal]
tab :: Int -> ShowS
tab 0 = id
tab (n+1) = showChar ' ' . tab n
showRow :: [Int] -> ShowS
showRow [] = showChar '\n'
showRow (n:ns) = shows n . showChar ' ' . showRow ns
showTriangle 1 (t:_) = showRow t
showTriangle (n+1) (t:ts) = tab n . showRow t . showTriangle n ts
main = appendChan stdout "Number of rows: " abort $
readChan stdin abort $ \input ->
appendChan stdout
(showTriangle (read (head (lines input))) pascal "")
abort done
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