How can I find the indexes of an element in Haskell list

问题

Here is a Haskell list:

[[1],[3,5],[],[1,9],[3,5],[9,7],[1,9]]

I want to find the exact index of its elements. I tried to use elemIndex but it doesn't give the correct index when I try to find duplicated element like [3,5] and [1,9].

回答1:

Is this what you want?

> elemIndices  [3,5] [[1],[3,5],[],[1,9],[3,5],[9,7],[1,9]]
[1,4]

来源：https://stackoverflow.com/questions/27514828/how-can-i-find-the-indexes-of-an-element-in-haskell-list