Hi,
I have
sumIs2020P1' xs = do
x <- xs
y <- xs
guard (x + y == 2020)
pure (x,y)
which has been desugared from a list comprehension
I would like to reduce this even more using >>=
So I do
sumIs2020P1'' xs = (a,b) where
(a,b):rest = filter (\(x,y) -> x + y == 2020) pairs
pairs = xs >>= \x ->
xs >>= \y ->
pure (x,y)
but really I would like the guard to be within the >>= sections but I could not work out
how to do it!
i.e. I’m looking for something like (pseudo code)
pairs = xs >>= \x ->
xs >>= \y ->
if (x + y == 2020) then pure (x,y) else DO_NOTHING
which would then allow the filter to be removed.
Many Thanks
Mike