Haskell program simple game

Question

I am very new in haskell-programming. I try to program a simple dice-game, but I don't know to do it in haskell.

 suc :: (Int,Int,Int) -> Int -> (Int,Int,Int) -> Bool

 suc  (a₁,a₂,a₃) c (d₁,d₂,d₃)

I want to consider each difference dᵢ - aᵢ (but not if aᵢ > dᵢ) and return False if (d1-a1)+(d2-a2)+(d3-a3) are larger than c. (if aᵢ > dᵢ then I sum up 0 instead the difference)

I try something like this:

suc :: (Int,Int,Int) -> Int -> (Int,Int,Int) -> Bool
suc (a1, a2, a3) c (d1, d2, d3) = ?????
    where diff1 = if (d1 > a1) then d1-a1       
          diff2 = if (d2 > a2) then d2-a2
          diff3 = if (d3 > a3) then d3-a3

Lee Duhem · Accepted Answer · 2014-04-26 13:30:55Z

2

Because in Haskell, else is not a optional part of an if expression, so you need to define diff1 as diff1 = if d1 > a1 then d1 - a1 else 0. Other two are similar.
Notes that > returns a Bool value, so you could just sum these three differences up and compare it with c, and use it as your condition.

There are several ways to define this function:

suc1 (a1, a2, a3) c (d1, d2, d3) = diff1 + diff2 + diff3 <= c
    where diff1 = if d1 > a1 then d1 - a1 else 0
          diff2 = if d2 > a2 then d2 - a2 else 0
          diff3 = if d3 > a3 then d3 - a3 else 0

suc2 (a1, a2, a3) c (d1, d2, d3) = sum diffs <= c
    where diff1 = max (d1-a1) 0
          diff2 = max (d2-a2) 0
          diff3 = max (d3-a3) 0
          diffs = [diff1, diff2, diff3]

suc3 (a1, a2, a3) c (d1, d2, d3) = sum (zipWith diff as ds) <= c
    where diff a d = max (d-a) 0
          as = [a1, a2, a3]
          ds = [d1, d2, d3]

edited Apr 26, 2014 at 13:30

answered Apr 26, 2014 at 13:03

Lee Duhem

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1 Comment

leftaroundabout Over a year ago

Nice! Of course, the third alternative would be much shorter if the arguments were already given as lists, as they maybe should.

kaan · Accepted Answer · 2014-04-27 00:05:10Z

1

How about this?

suc :: (Int,Int,Int) -> Int -> (Int,Int,Int) -> Bool
suc (a1, a2, a3) c (d1, d2, d3) = 
    ((if a1> d1 then 0 else d1-a1) + (if a2> d2 then 0 else d2-a2) + (if a3>d3 then 0 else d3-a3) > c )

Or alternatively

suc :: (Int,Int,Int) -> Int -> (Int,Int,Int) -> Bool
suc (a1, a2, a3) c (d1, d2, d3) = 
    max 0 (d1-a1) + max 0 (d2-a2) + max 0 (d3-a3) > c

edited Apr 27, 2014 at 0:05

kaan

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answered Apr 26, 2014 at 12:50

Tomas Pastircak

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4 Comments

kaan Over a year ago

instead of the if's you could try max 0 (d-a)

basti12354 Over a year ago

Great it works, I've only changed >c to <= c, now it's exactly what I want. Thanks a lot

Jon Purdy Over a year ago

It is possible to pull apart further: suc (a1, a2, a3) c (d1, d2, d3) = (> c) . sum . map (max 0) $ zipWith (-) [d1, d2, d3] [a1, a2, a3]

Tomas Pastircak Over a year ago

@JonPurdy You're definitely right it would work, and it would be a correct way to do for bigger data sets, but personally in this case I would prefer the way used in the answer, as the code is much more readable and not much longer.

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