Bug in users manual, 6.4.2, section on pattern guards

[Simon Marlow]

Matthew Cox wrote:
> One example given in this discussion is:
> 
> clunky env var1 var1 = case lookup env var1 of
>   Nothing -> fail
>   Just val1 -> case lookup env var2 of
>     Nothing -> fail
>     Just val2 -> val1 + val2
> where
>   fail = val1 + val2
> 
> this needs to be fixed to:
> 
> clunky env var1 var1 = case lookup env var1 of
>   Nothing -> fail
>   Just val1 -> case lookup env var2 of
>     Nothing -> fail
>     Just val2 -> val1 + val2
> where
>   fail = var1 + var2   <<<< (Added for emphasis)
> 
> I didn't see it myself on the first readthrough, but I was comparing structure between two examples
> and noticed the discrepency. Let's fix it for correctness' sake.

fixed; thanks.

Simon