At the risk of useless bikeshedding... might I suggest "r" as a mnemonic for "result"?<div><br></div><div>foldl :: (a -> r -> r) -> r -> [a] -> r</div><div>foldr :: (r -> a -> r) -> r -> [a] -> r</div>
<div><br clear="all">-- Dan Burton<br>
<br><br><div class="gmail_quote">On Sun, Oct 14, 2012 at 12:33 PM, Andreas Abel <span dir="ltr"><<a href="mailto:andreas.abel@ifi.lmu.de" target="_blank">andreas.abel@ifi.lmu.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
+1 to all.<div class="HOEnZb"><div class="h5"><br>
<br>
On 14.10.12 6:53 PM, Bas van Dijk wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
+1<br>
<br>
There are a few other functions in Data.List that could benefit from<br>
the same treatment:<br>
<br>
mapAccumL :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])<br>
mapAccumL :: (acc -> a -> (acc, b)) -> acc -> [a] -> (acc, [b])<br>
<br>
mapAccumR :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])<br>
mapAccumR :: (acc -> a -> (acc, b)) -> acc -> [a] -> (acc, [b])<br>
<br>
genericLength :: Num i => [b] -> i<br>
genericLength :: Num i => [a] -> i<br>
<br>
genericSplitAt :: Integral i => i -> [b] -> ([b], [b])<br>
genericSplitAt :: Integral i => i -> [a] -> ([a], [a])<br>
<br>
genericIndex :: Integral a => [b] -> a -> b<br>
genericIndex :: Integral i => [a] -> i -> a<br>
<br>
I'm not sure if we should change mapAccumL/R since 'a' and 'acc' are<br>
maybe too similar.<br>
<br>
Bas<br>
<br>
On 14 October 2012 16:28, Gábor Lehel <<a href="mailto:illissius@gmail.com" target="_blank">illissius@gmail.com</a>> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Currently we have:<br>
<br>
foldl :: (a -> b -> a) -> a -> [b] -> a<br>
<br>
foldr :: (a -> b -> b) -> b -> [a] -> b<br>
<br>
I find this confusing. My brain doesn't do automatic alpha-renaming,<br>
so I end up thinking that these types are very different because they<br>
look very different. In fact, they are almost the same.<br>
Embarrassingly, it took me longer than it took to understand monads,<br>
GADTs, PolyKinds, and several other things before I realized it!<br>
<br>
So I propose that we use 'a' consistently to denote the type of the<br>
list elements, and 'b' to denote the type of the result:<br>
<br>
foldl :: (b -> a -> b) -> b -> [a] -> b<br>
<br>
foldr :: (a -> b -> b) -> b -> [a] -> b<br>
<br>
making it obvious that the only difference is the order of parameters<br>
to the accumulator.<br>
<br>
The total change would be to replace<br>
<br>
Prelude.foldl :: (a -> b -> a) -> a -> [b] -> a<br>
Prelude.scanl :: (a -> b -> a) -> a -> [b] -> [a]<br>
Data.List.foldl' :: (a -> b -> a) -> a -> [b] -> a<br>
Data.Foldable.foldl :: (a -> b -> a) -> a -> t b -> a<br>
Data.Foldable.foldl' :: (a -> b -> a) -> a -> t b -> a<br>
<br>
with<br>
<br>
Prelude.foldl :: (b -> a -> b) -> b -> [a] -> b<br>
Prelude.scanl :: (b -> a -> b) -> b -> [a] -> [b]<br>
Data.List.foldl' :: (b -> a -> b) -> b -> [a] -> b<br>
Data.Foldable.foldl :: (b -> a -> b) -> b -> t a -> b<br>
Data.Foldable.foldl' :: (b -> a -> b) -> b -> t a -> b<br>
<br>
I've attached a patch.<br>
<br>
Discussion period: 2 weeks<br>
<br>
Previously discussed at: <a href="http://www.reddit.com/r/haskell/comments/10q2ls/" target="_blank">http://www.reddit.com/r/<u></u>haskell/comments/10q2ls/</a><br>
<br>
--<br>
Your ship was destroyed in a monadic eruption.<br>
<br>
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</blockquote>
<br>
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</blockquote>
<br></div></div><div class="im HOEnZb">
-- <br>
Andreas Abel <>< Du bist der geliebte Mensch.<br>
<br>
Theoretical Computer Science, University of Munich<br>
Oettingenstr. 67, D-80538 Munich, GERMANY<br>
<br>
<a href="mailto:andreas.abel@ifi.lmu.de" target="_blank">andreas.abel@ifi.lmu.de</a><br>
<a href="http://www2.tcs.ifi.lmu.de/~abel/" target="_blank">http://www2.tcs.ifi.lmu.de/~<u></u>abel/</a><br>
<br></div><div class="HOEnZb"><div class="h5">
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