lookaheads.clj

; helper functions are missing, be it for char ranges or for lookaheads
; however this snippet demoes:
; * error-correction (the change in correction between the 3rd and 4th case shows that parsnip looks for a minimal deletion)
; * lookahead
=> (let [alpha (fn [c] (<= (int \a) (int c) (int \z)))
         p (parser :map
             {:map ["{" (* :sym (? :ws) :sym) "}"]
              :ws (+ " ")
              :sym [(+ (->InlineAsm [:PRED alpha])) 
                    (->InlineAsm [:PEEK (complement alpha)])]})]
     (doseq [input ["{aaaa}" "{aa aa}" "{a aa a}" "{a  aa a}"]]
       (prn input '-> (p input))))

"{aaaa}" -> [[:map "{" [:skip "aaaa"] "}"]]
"{aa aa}" -> [[:map "{" [:sym "aa"] [:ws " "] [:sym "aa"] "}"]]
"{a aa a}" -> [[:map "{" [:sym "a" [:skip " "] "aa"] [:ws " "] [:sym "a"] "}"]]
"{a  aa a}" -> [[:map "{" [:sym "a"] [:ws "  "] [:sym "aa" [:skip " "] "a"] "}"]]