2 Dimensional Mutable Array in Haskell and coloring the output with ANSI

Question

I find it a little difficult to understand the Haskell world, so I would really appreciate some help!

I want to create 2 dimensional array of Chars (a matrix 10x10 of symbols) and it should be mutable, so I tried this:

import Data.Array.IO
arr <- newArray ((1,10), (1,10)) '!' :: IO (IOArray (Int, Int) Char)
a <- readArray arr (1,1)

but it didn't worked out. Could you please tell me how to create the array and how to access its members, or if this isn't a good way, another way to do this?

And also I would like to ask if there is a way to color some of the elements in the array in a different color. I imported System.Console.ANSI but I'm not quite sure how exactly to color what I want to be in a different color. A example of outputting a red letter would be really helpfull.

Thank you very much in advance! :)

Two things: First, why do you want a mutable array? Chances are you actually don't. Second, coloring "elements of the array" makes no sense as such. That's an output issue, and a completely separate question. — C. A. McCann
– C. A. McCann, Commented Jan 4, 2013 at 17:35
I'm not sure if it has to be mutable, I would like to try to implement game of life and the array will be changing on each iteration, so I thought that it's better to be mutable. As for the coloring, I wanted the cells which are dead and alive to be in different colors. I know that it is another topic, but I would feel a bit guilty for posting two haskell questions at the same time. — Faery
– Faery, Commented Jan 4, 2013 at 18:28
You're more likely to get helpful answers if your question has a single purpose and clearly explains the problem you're trying to solve. I'd suggest clarifying your overall goal (instead of assuming a particular kind of solution) and posting a separate question about colored output, possibly after getting the rest of the program working if you're worried about posting too many questions at once. — C. A. McCann
– C. A. McCann, Commented Jan 4, 2013 at 18:39
For a "Game of Life", if memory serves, an array is not the best choice (and that comes from someone who loves arrays, in particular mutable arrays [the ST kind, not the IO kind, though]). There are typically so many free cells that scanning them is much more expensive than a lookup in e.g. a Map. — Daniel Fischer
– Daniel Fischer, Commented Jan 4, 2013 at 20:08

dave4420 · Accepted Answer · 2013-01-04 18:37:15Z

This compiles and runs without error on my laptop.

import Data.Array.IO       -- from the array package
import System.Console.ANSI -- from the ansi-terminal package

main :: IO ()
main = do
        arr <- newArray ((1,1), (10,10)) '!' :: IO (IOArray (Int, Int) Char)
        -- You had ((1,10), (1,10)), in the line above.
        -- That meant (1,10) was the only valid index!
        ch <- readArray arr (1,1)
        setSGR [SetColor Foreground Dull Red]   -- set foreground colour to red
        putStr [ch]
        setSGR []                               -- reset colours
        putStrLn ""

I second C. A. McCann's suggestion of using normal, immutable arrays instead of mutable arrays. (Unfortunately I have little experience of using arrays in Haskell, so I'll leave it to someone else to suggest how to compute an updated array from the old array in a single step.)

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