Hi all, I was looking for an APL-style "iota" function for array indices. I noticed "range" from Data.Ix which, with a zero for the lower bound (here (0,0)), gives the values I need:
let (a,b) = (2,3)
index ((0,0),(a-1,b-1))
[(0,0),(0,1),(0,2),(1,0),(1,1),(1,2)]
However, I need the results as a list of lists rather than a list of tuples; and my input is a list of integral values. I ended up writing the following function instead. The function isn't long, but longer than I first expected. Did I miss a simpler approach? iota :: (Integral a) => [a] -> [[a]] iota is = let count = product is tups = zip (tail $ scanr (*) 1 is) is buildRepList (r,i) = genericTake count $ cycle $ [0..i-1]
= genericReplicate r
lists = map buildRepList tups in transpose lists
length $ iota [2,3,4]
24
Thanks, Paul