Saturday, September 27, 2008
Sunday, September 7, 2008
Either is standard Haskell datatype defined by
data Either a b = Left a | Right b
Let's define Either monad as follows:
instance Monad (Either a) where return = Right x >>= f = case x of Left _ -> x Right r -> f r
This means we fix the type of
Left part and consider
Either a as monadic constructor of kind
* -> *. Binding operator has the following sense: the function transforms data if it's
Right and leaves it unchanged if it's
Left (it's similar to
Right corresponding to
Left corresponding to
Now the puzzle itself. 1) Why the above code won't typecheck and 2) how to make it valid with minimal changes?
The answer on the first question was obvious for me, and I thank
#haskellers for giving me solution to the second.
Friday, September 5, 2008
The opening of 30th cycle of seminars on discrete mathematics will be at 16.00 on September 8 (auditorium 73, Odessa State University main building).
Prof. Melnikov (Minsk) will give a lecture on teaching discrete mathematics in high school.
The chair of seminars — prof. Zykov (Odessa).
The cycle will last till September 12.