ci-lex.rkt

(define-for-syntax (char-ci char)
  `(union ,(char-upcase char)
          ,(char-downcase char)))

(define-for-syntax (string-ci str)
  `(concatenation ,@(map char-ci (string->list str))))

(define-lex-trans :char-ci (λ (stx)
                             (match (syntax->datum stx)
                               [(list :char-ci char) (datum->syntax stx (char-ci char))])))

(define-lex-trans :string-ci (λ (stx)
                               (match (syntax->datum stx)
                                 [(list :string-ci str) (datum->syntax stx (string-ci str))])))

(define-lex-trans :strings-ci (λ (stx)
                                 (match (syntax->datum stx)
                                   [(list :strings-ci ss ..1) (datum->syntax stx `(union ,@(map string-ci ss)))])))