This matrix transposition function works, but I'm trying to understand its step by step execurtion and I don't get it.

    transpose:: [[a]]->[[a]]
    transpose ([]:_) = []
    transpose x = (map head x) : transpose (map tail x)

with 

transpose [[1,2,3],[4,5,6],[7,8,9]]

it returns:

 [[1,4,7],[2,5,8],[3,6,9]]

I don't get how the concatenation operator is working with map. It is concatenating each head of x in the same function call? How?

is this 

(map head x)

creating a list of the head elements of each list?

algorithm list haskell
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