Re: [Haskell-cafe] A question about monad laws

Hi Kashyap,

Could someone please help me get a better understanding of the necessity of monads complying with these laws?

Maybe it helps to write them in do-notation. Once written like this, it becomes clear(er?) that do-notation would be much less intuitive if the laws would not hold: Left Unit: return x >>= \y -> f y  =  f x     do y <- return x        f y   = do f x Right Unit: a >>= \x -> return x  =  a     do x <- a        return x   = do a Associativity: (a >>= \x -> f x) >>= \y -> g y  =  a >>= \x -> (f x

...

= \y -> g y)     do y <- do x <- a                f x g y = do x <- a y <- f x g y

So, at least, the monad laws ensure that do-notation behaves as one would expect. Sebastian