1 files changed, 24 insertions, 0 deletions
diff --git a/progs/demo/pascal.hs b/progs/demo/pascal.hs
new file mode 100644
index 0000000..a26e9c9
--- /dev/null
+++ b/progs/demo/pascal.hs
@@ -0,0 +1,24 @@
+{- 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
+