It's whatever you're used to, but using sexprs means you don't need to write parsers because you have the read function. In Lisp, it's important to give the u

It's whatever you're used to, but using sexprs means you don't need to write parsers because you have the read function. In Lisp, it's important to give the user access to the parse tree. Since the S-expression syntax for Lisp was chosen, there have been at least three documented attempts to replace it: Lisp 2, CGOL, and Dylan. Lisp 2 syntax wasn't implemented and was only ever used in textbooks, and CGOL and Dylan were never popular and are no longer used. All Lisps today use S-expressions (but Clojure has [] and {} as well as ()), as do some Prologs, as well as a few other languages such as CLIPS. Readability is taken care of by the prettyprinter. For arithmetic expressions, I agree infix is easier to read because that's what maths uses. For complex formulae, I wrote a Lisp macro which accepts infix notation and I'm sure other Lispers have done likewise.