[Haskell-cafe] Please add a method for optimized concat to the Semigroup class

[Holger Siegel]

Am 03.05.2011 um 13:39 schrieb Stephen Tetley:

> Does it have an obvious default implementation, bearing in mind it we
> might really want a total function?
> 
> sconcat []     = error "Yikes - I wish this was total!"
> sconcat [a]    = a
> sconcat (a:as) = a <> sconcat as

You have to provide the "neutral" element by yourself:

infixl 4 <>>

a <>> [] = a
a <>> (b:bs) = a <> b <>> bs

> 
> Best wishes
> 
> Stephen
> 
> On 3 May 2011 12:12, Yitzchak Gale <gale at sefer.org> wrote:
> [SNIP]
>> It has the obvious default implementation,
>> but allows for an optimized implementation for
>> specific instances. That turns out to be something
>> that comes up all the time (at least for me) in
>> real life.
> 
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