Clojure cats append nil behaviour

Question

I am using funcool/cats, append monoid with the following code :

(m/mappend (maybe/just [1 2 3])
             nil
             (maybe/just [4 5 6])
             (maybe/nothing)) ;;=> #<Just [1 2 3 4 5 6]>

What is the rationale for treating nil as maybe/nothing ?

Note : the version is [funcool/cats "1.2.1"]

score 1 · Accepted Answer · answered Mar 03 '16 at 14:17

From the commit log, it seems like it's

just for (sic) avoid accidental null pointer exceptions

Given the fact that nil is both a value and a type, we have extended the nil type to be equivalent to Maybe monad’s Nothing.

1 Answers1