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I have a function called bounds1Accum. this function works great

bounds1Accum ::  [Integer] -> Integer -> Integer -> (Integer, Integer)
bounds1Accum l min max = (minimum (min:l), maximum (max:l))

What I am having problems with is I need another function called bounds1 which will take in just a list and return a min max pair. This function is supposed to wrap around bounds1accum and check to first see if the list being passed to it is empty or not. if the list is empty it will return Nothing or it will Just return the result of calling the bounds1Accum function.

I need two cases and for my signature I have

bounds1 :: [l] -> Maybe(min,max)
bounds1 [] = Nothing (which I am unsure if this will be correct)

then the 2nd case is where I am stumped I originally had 

bounds1 l  min max  = if null l then Nothing else Just $ bounds1 bounds1Accum min max

but this does not even compile so if anyone can offer suggestions or another way I can look at this problem it would be great. This is for an assignment so I do not want the answer but more so just guidance or help solving the problem. Thank you

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  • I would suggest writing it with guards, rather than if-then-else. Mostly because that looks more like piece-wise function definition, which is what we're trying to do. Commented Apr 19, 2013 at 16:17

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In the second case, you do not have min and max as arguments. You have to take those values from the list.

The if is unnecessary, since you already handle the empty list in the first case.

And why is there bounds1 before the use of bounds1Accum?

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7 Comments

so bounds1 [] = Nothing is okay for first case? and case to should be bounds1 l = Just $ bounds1 bounds1Accum l min max? I put bounds1 first because it is supposed to wrap around bounds1Accum. Maybe I am thinking of it the wrong way.
I can add the actual needed specifications if that would be more helpful.
@benzo_nerd I think wrapping bounds1Accum just means calling it with the right arguments. And yes, first case is OK.
when I try to run this it tells me I have wrong number of arguments for case # 2 and my signature. my case #2 looks like this bounds1 l = Just $ bounds1 bounds1Accum l min max I tried switching bounds1 and bounds1Accum too with same result
Again, I don't understand what is bounds1 doing just in front of bounds1Accum. BTW, are you sure bound1Accum is implemented as it should? It doesn't do what its name suggests.
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