A rule to transpose pattern and target of a rule?

Question

I am trying to write a Mathematica function that will take a rule such as a->b to `b->a'. Can this be done?

score 3 · Answer 1 · answered Jul 03 '17 at 22:31

3

Use a pattern to deconstruct the Rule, and reconstitute it backwards in your function body.

f[Rule[a_, b_]] := Rule[b, a]

answered Jul 03 '17 at 22:31

John Doty

eldo · Answer 2 · 2017-07-03T22:39:25.863

3

a -> b // Reverse

Or

(a -> b)[[{2, 1}]]

Or

 a -> b /. (x_ -> y_) -> y -> x

edited Jul 03 '17 at 22:39

answered Jul 03 '17 at 22:33

eldo

2 Answers2