Matching with zero or more matches with rx

Question

Am using rx and am getting

(string-match-p
(rx bos ( "a" "b") eos)
"a")
==> 0
 
(string-match-p
(rx bos (* "a" "b") eos)
"b")
==> nil

Why is this?

Answer 1

Not sure what you are trying to do. May be you meant this

(string-match-p (rx bos (or "a" "b") eos) "a")

Note the or operator there.

I usually prefer to write it like this

(string-match-p (rx
                 (seq
                  bos
                  (or "aa" "bb" "cc")
                  (zero-or-more any)
                  eos))
                "aand")

Note the use of operators seq and or.

I copied what you provided in to *scratch* buffer and I did M-x eval-buffer and I get this

Debugger entered--Lisp error: (error "Bad rx operator ‘\"a\"’")
  signal(error ("Bad rx operator ‘\"a\"’"))
  error("Bad rx operator `%S'" "a")
  rx--translate-form(("a" "b"))
  rx--translate(("a" "b"))
  mapcar(rx--translate (bos ("a" "b") eos))
  rx--translate-seq((bos ("a" "b") eos))
  rx--translate-form((seq bos ("a" "b") eos))
  rx--translate((seq bos ("a" "b") eos))
  rx--to-expr((seq bos ("a" "b") eos))