[Haskell-cafe] Is the #functional programming paradigm antithetical to efficient strings? #Haskell

Alex Belanger i.caught.air at gmail.com
Mon Jul 11 13:33:16 UTC 2016


That's not just about Haskell, it's C.S. in general.

You're always going to make space and time tradeoffs.

Funny how the same constraints appear in physics; I wonder if it is trying
to tell us something...

- nitrix
On Jul 11, 2016 8:54 AM, "David Fox" <dsf at seereason.com> wrote:

On Sun, Jul 10, 2016 at 11:44 AM, KC <kc1956 at gmail.com> wrote:

> Is the #functional programming paradigm antithetical to efficient strings?
> #Haskell
>
 ‚ÄčI can certainly see how it might seem so.  Our main string
representation‚Äč uses about 10 times more memory than seems necessary, and
is relatively fast, though probably not compared to C.  Recently I spent
some time looking into how to reduce this memory overhead, and I modified
the pretty library (https://github.com/ddssff/pretty/tree/textdetails) so
it could use any type that was an instance of ListLike and StringLike (
https://github.com/JohnLato/listlike).  Then I tried the UnitLargeDoc test
with several different data types.  This just concatenates a list of ten
million "Hello" strings.  Using String this happens in about 5 seconds.
Using strict or lazy Text it immediately blew the stack.  When I increased
the stack size to over 1GB it took minutes to complete.  When I used the
Data.Text.Lazy.Builder type instead it took about 30 seconds to complete.
Results with utf8 encoded ByteStrings were siimilar.

When I mentioned some of this, I was told "different data structures for
different purposes", which sort of makes sense, but honestly if Haskell is
a language where you have to sit down and choose a representation every
time you want to build some text, I get a bit discouraged.

So is functional programming antithetical to efficient strings?  In theory
maybe not, but I would love to see some hard evidence.

</rant>

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