Using readtable for parsing works pretty well:

#lang racket (define readtable/comma (make-readtable #f #\, #\space #f)) (define read-table/brace (make-readtable readtable/comma #\{ 'terminating-macro (λ (ch port src line col pos) (~a "{" (string-join (sort (map ~a (read/recursive port ch readtable/comma)) string<?) ",") "}")))) (define s "{{1,2}, {2,3}, {3,(4)}, {1,0}, {5,def}, {5,abc}}") (parameterize ([current-readtable read-table/brace]) (read (open-input-string s))) ; "{{(4),3},{0,1},{1,2},{2,3},{5,abc},{5,def}}"