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Build Status Clojars Project

Grammar-based Clojure reader.

Parcera can safely read any Clojure file without any code evaluation.

Parcera uses the wonderful Antlr4 as its parsing engine and focuses on the grammar definition instead.


Add [org.antlr/antlr4-runtime "4.7.1"] to your dependencies in addition to parcera. Parcera assumes that this dependency will be in the classpath to avoid collisions.

(ns example.core
  (:require [parcera.core :as parcera]))

;;parse clojure code from a string
(parcera/ast (str '(ns parcera.core
                     (:require [ :as bar]
                               [ :as data]
                               [clojure.string :as str]))))

;; => returns a data structure with the result from the parser
  (:symbol "ns")
  (:whitespace " ")
  (:symbol "parcera.core")
  (:whitespace " ")
   (:simple_keyword "require")
   (:whitespace " ")
    (:symbol "")
    (:whitespace " ")
    (:simple_keyword "as")
    (:whitespace " ")
    (:symbol "bar"))
   (:whitespace " ")
   (:vector (:symbol "") (:whitespace " ") (:simple_keyword "as") (:whitespace " ") (:symbol "data"))
   (:whitespace " ")
   (:vector (:symbol "clojure.string") (:whitespace " ") (:simple_keyword "as") (:whitespace " ") (:symbol "str")))))

;; get meta data from the parsed code
(meta (second (parcera/ast (str :hello))))
#:parcera.core{:start {:row 1, :column 0}, :end {:row 1, :column 6}}

;; convert an AST back into a string
(parcera/code [:symbol "ns"])
;; "ns"

note: parcera is a bit permissive for symbols and keywords, you should be able to parse any valid Clojure file however, I cannot guarantee that an invalid symbol/keyword will yield a failure. This is because Clojure's reader is very stateful and embedding all those rules into the grammar would make it prohibitively complex.


  • to get you setup check the travis file which already contains a full setup from scratch.
  • the project contains a benchmark which should be the decision factor for performance issues.
  • please follow Clojure's Etiquete for issues and pull requests

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