Dear Haskell implementors, Consider the compilation flag -allow-extension-for-bottom which changes the language meaning so that allows to ignore the bottom value. For example, the programs (1) (\ x -> (if p x then foo (g x) else foo (h x)) ) and (2) (\ x -> foo ((if p x then g x else h x)) ) become equivalent, and many program transformations become possible. I suspect that after compiling and running of a program under -allow-extension-for-bottom the user will discover many helpful information about the original program. For example, under -allow-extension-for-bottom it may run 1000 times faster, and then, the user finds out what to change to have a 1000 times speed-up for the original program for the standard Haskell. Thus, in my particular practical example, it is evident to me that it is better to specify (2). But many similar effects are hard to find out without compiling under -allow-extension-for-bottom. Maybe, the compiler could issue the warnings like, say, "Consider factoring `if' in ... This may improve ... " ? Copy, please, the answer to mechvel@botik.ru, ----------------- Serge Mechveliani mechvel@botik.ru