[Haskell-beginners] Mutable grid

[Magnus Therning]

How did it go?

When I solved that AoC problem I ended up using the matrix package:
http://hackage.haskell.org/package/matrix

/M


On 19 Dec 2016 7:31 pm, "mike h" <mike_k_houghton at yahoo.co.uk> wrote:

> Thanks for the pointers - I’ll take a look.
>
> The background to this is one of the puzzles on Advent Of Code 2016 Q.8.
> https://adventofcode.com/2016/day/8
>
> There are (several hundred) sequential  operations on a grid 50 x 6
>  - initially all zeroes
> e.g.
> rotate row y=0 by 4
> rect 2x1 — sets sub grid from (0,0) to (2,1) to all 1s
> rotate column x=35 by 1
>
> I’m fine about parsing the input to a data structure and executing
> them i.e.
>
> evalExpr :: Expr -> Screen -> Screen     — screen is essentially [[Int]]
> evalExpr e s =
>     case e of
>         (Rect   r c ) ->     evalRect   r c s
>         (RotRow r by) -> evalRotRow r by s
>         (RotCol c by) -> evalRotCol c by s
>         (NOP        ) -> id s
>
> rotating a row was simple enough, code to  rotate column a bit untidy and
> not very nice. The
> evalRect  - which sets values to one in the rectangle of size r x c
> starting at (0,0) top left - triggered the original question.
>
>
> At this point  my knowledge of Haskell is being pushed (which is good) but
> I have a feeling that
> my approach is not ‘correct’ once it gets beyond the parsing. Should each
> of the evalRect, evalRotRow and evalRotCol be called with a Screen (i.e.
> the grid at the root of this question)?
> Is the state monad a fit for this problem?
> Should I change my approach or is using vector the way forward?
>
> Many thanks
>
> Mike
>
>
>
>
>
> On 19 Dec 2016, at 15:27, Michael Orlitzky <michael at orlitzky.com> wrote:
>
> On 12/19/2016 08:10 AM, mike h wrote:
>
> Hi,
>
> I’m looking a problem where I have an NxN grid of ints. I need a
> function like setValue x y newVal
>
> I have tried using [[Int]] but it does become messy when splitting ,
> dropping and then ++ back together.
>
> What other options are available to represent a mutable grid?
>
>
> Mutable vectors (from the vector[1] package) are an obvious choice. When
> I had to do something similar, I wound up going all the way to repa[2],
> which magically turns all of your grid operations into parallel ones.
>
>
> [1] https://hackage.haskell.org/package/vector
> [2] https://hackage.haskell.org/package/repa
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/beginners/attachments/20161224/1675bbd2/attachment.html>