[Haskell-cafe] Expanding do notation

[Bertram Felgenhauer]

David F. Place wrote:
> main' n = let p = permutations [1..n]
> 	      		in do mapM_ (putStrLn . concatMap show) $ take 30 p
> 		    	          putStr $ "Pfannkuchen(" ++ show n ++ ") = "
> 		    	          putStrLn . show $ foldl' (flip (max . 
> 		    	          steps 0)) 0 p
> 
> In the original version, the author called 'permutations' twice and  
> didn't create a variable binding.

As a side note, I expected GHC to do common subexpression elimination and
evaluate permutations [1..n] only once, caching the 30 results that are
used twice. I didn't try to find out whether it actually did though.

Bertram