From 4e987026148fe65c323afbc93cd560c07bf06b3f Mon Sep 17 00:00:00 2001
From: Yale AI Dept <ai@nebula.cs.yale.edu>
Date: Wed, 14 Jul 1993 13:08:00 -0500
Subject: Import to github.

---
 progs/demo/pascal.hs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 progs/demo/pascal.hs

(limited to 'progs/demo/pascal.hs')

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
+
-- 
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