star-directive in clojure.pprint/cl-format with an at-prefix ("~n@*") do not obey its specifications


  • Type: Defect Defect
  • Status: Closed Closed
  • Priority: Minor Minor
  • Resolution: Completed
  • Affects Version/s: Release 1.4, Release 1.5
  • Fix Version/s: Release 1.8
  • Component/s: None
  • Labels:
  • Patch:
    Code and Test
  • Approval:


The star-directive in clojure.pprint/cl-format with an at-prefix (~n@*) does not obey its specifications according to Common Lisp the Language, 2nd Edition. There are two bugs within ~n@* as of right now:

  1. When ~n@* is supposed to jump forward over more than one argument, it jumps one step backward as if it had seen ~:*. For instance, (cl-format nil "~D ~3@*~D" 0 1 2 3) will return "0 0" and not "0 3" as expected.
  2. When ~@* is seen, the formatter is supposed to jump to the first argument (as n defaults to 0, see specification linked above). However, whenever a ~@*-directive is seen, the formatter jumps to the second argument instead.

Inside a clean Clojure repl, perform these steps:

user=> (require '[clojure.pprint :refer [cl-format]])
user=> (cl-format nil "~D ~3@*~D" 0 1 2 3)
"0 0"                                           ;; Expected: "0 3"
user=> (cl-format nil "~D~D~D~D ~@*~D" 0 1 2 3)
"0123 1"                                        ;; Expected: "0123 0"

The format strings which reproduce the problem has been compared with the format function from the Common Lisp implementations SBCL, CLisp and Clozure. All of them print the expected output.

Patch: clj-1134-star-directive-in-cl-format.txt

Screened by: Alex Miller



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