Question

I have some chars, for example [“ab”], and I just have two number, zero and one.
And I want to get an answer like

[[('a', 1), ('b', 1)],
 [('a', 0), ('b', 1)],
 [('a', 1), ('b', 0)],
 [('a', 0), ('b', 0)]]

I am a beginner, could someone help me?

Thankyou very much.

Answer 1

The most interesting part is generating the list of all possible sequences of 0 and 1; one way is via replicateM:

> replicateM 2 [1,0]
[[1,1],[1,0],[0,1],[0,0]]

You can use map and zip from there:

> map (zip "ab") (replicateM 2 [1,0])
[[('a',1),('b',1)],[('a',1),('b',0)],[('a',0),('b',1)],[('a',0),('b',0)]]

To match your answer exactly, you’d have to do a tiny bit of extra munging:

> map (zip "ab" . reverse) (replicateM 2 [1,0])
[[('a',1),('b',1)],[('a',0),('b',1)],[('a',1),('b',0)],[('a',0),('b',0)]]