[valw]

Author here. I could be wrong of course, but this stems from my experience in using a REPL from JavaScript. I hit 2 sorts of hurdle with mutability there: 1- I wasn't sure what I was viewing in the REPL was what the code of interest was perceiving, could have been changed afterwards and 2- immutable values were more suited for exploratory work due to their speculative nature, e.g I could try a function calls with variants of a data structure without 'committing' to them. Maybe I had a bad REPL experience in JS and blamed it on immutability; OTOH, maybe other people had a great REPL experience in Common Lips for other reasons, and attribute it to mutability. This certainly makes me want to give a new try to Common Lisp :)