+1 to all.
On 14.10.12 6:53 PM, Bas van Dijk wrote:
+1
There are a few other functions in Data.List that could benefit from
the same treatment:
mapAccumL :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
mapAccumL :: (acc -> a -> (acc, b)) -> acc -> [a] -> (acc, [b])
mapAccumR :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
mapAccumR :: (acc -> a -> (acc, b)) -> acc -> [a] -> (acc, [b])
genericLength :: Num i => [b] -> i
genericLength :: Num i => [a] -> i
genericSplitAt :: Integral i => i -> [b] -> ([b], [b])
genericSplitAt :: Integral i => i -> [a] -> ([a], [a])
genericIndex :: Integral a => [b] -> a -> b
genericIndex :: Integral i => [a] -> i -> a
I'm not sure if we should change mapAccumL/R since 'a' and 'acc' are
maybe too similar.
Bas
On 14 October 2012 16:28, Gábor Lehel <illissius@gmail.com> wrote:
Currently we have:
foldl :: (a -> b -> a) -> a -> [b] -> a
foldr :: (a -> b -> b) -> b -> [a] -> b
I find this confusing. My brain doesn't do automatic alpha-renaming,
so I end up thinking that these types are very different because they
look very different. In fact, they are almost the same.
Embarrassingly, it took me longer than it took to understand monads,
GADTs, PolyKinds, and several other things before I realized it!
So I propose that we use 'a' consistently to denote the type of the
list elements, and 'b' to denote the type of the result:
foldl :: (b -> a -> b) -> b -> [a] -> b
foldr :: (a -> b -> b) -> b -> [a] -> b
making it obvious that the only difference is the order of parameters
to the accumulator.
The total change would be to replace
Prelude.foldl :: (a -> b -> a) -> a -> [b] -> a
Prelude.scanl :: (a -> b -> a) -> a -> [b] -> [a]
Data.List.foldl' :: (a -> b -> a) -> a -> [b] -> a
Data.Foldable.foldl :: (a -> b -> a) -> a -> t b -> a
Data.Foldable.foldl' :: (a -> b -> a) -> a -> t b -> a
with
Prelude.foldl :: (b -> a -> b) -> b -> [a] -> b
Prelude.scanl :: (b -> a -> b) -> b -> [a] -> [b]
Data.List.foldl' :: (b -> a -> b) -> b -> [a] -> b
Data.Foldable.foldl :: (b -> a -> b) -> b -> t a -> b
Data.Foldable.foldl' :: (b -> a -> b) -> b -> t a -> b
I've attached a patch.
Discussion period: 2 weeks
Previously discussed at: http://www.reddit.com/r/haskell/comments/10q2ls/
--
Your ship was destroyed in a monadic eruption.
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