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1 files changed, 21 insertions, 0 deletions

diff --git a/progs/demo/improved-add.hs b/progs/demo/improved-add.hs
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+++ b/progs/demo/improved-add.hs
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+-- this is an interactive program to read in two numbers and print their sum.
+
+module Main where
+
+main = readChan stdin abort $ \userInput -> 
+       let inputLines = lines userInput in
+        readInt "Enter first number: " inputLines $ \num1 inputLines1 ->
+        readInt "Enter second number: " inputLines1 $ \ num2 _ ->
+        appendChan stdout ("Their sum is: " ++ show (num1 + num2)) abort done
+
+readInt :: String -> [String] -> (Integer -> [String] -> Dialogue) -> Dialogue
+
+readInt prompt inputLines succ =
+  appendChan stdout prompt abort $
+  case inputLines of
+     (l1 : rest) -> case (reads l1) of
+                       [(x,"")] -> succ x rest
+                       _        -> appendChan stdout
+	                              "Error - retype the number\n" abort $
+	                           readInt prompt rest succ
+     _          -> appendChan stdout "Early EOF" abort done