Does anyone want intersperse for Data.Sequence?

John Lato jwlato at
Mon Dec 29 00:02:23 UTC 2014

It depends what you mean. Seq has nice asymptotics but quite poor constant
Do you consider DList as requiring a separate building phase?  If so, the
answer is quite possibly that the data structure you want doesn't exist.
But for most code I think the existing solutions are good enough (and
performance requirements lax enough) that nobody has put much effort into
anything better.

John L.

On 08:30, Sun, Dec 28, 2014 Greg Weber <greg at> wrote:

> I want an interface that supports efficient appending without requiring a
> separate building phase or other hassles. Does this not exist?
> I get that a library author might want to deal with the hassle of
> alternatives. But as an application author there are times that all I care
> about is a clean and simple interface that supports efficient appends.
> On Sun, Dec 28, 2014 at 1:01 AM, Roman Cheplyaka <roma at> wrote:
>> On 27/12/14 17:03, Greg Weber wrote:
>> > Sequence is not used nearly enough.
>> Not really. Seq has high constant factors and for small sizes is often
>> slower than plain lists. Nor is it space-efficient (for big sizes).
>> It probably has its use cases, but most of the time you'd be better off
>> with one of the other choices:
>> * plain old lists
>> * difference lists (trees)
>> * lists "without remorse"
>> * vectors
>> * lazy vectors (lists of vectors)
>> Roman
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