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Article contents:[[tags: eggs]] [[toc:]] == json-abnf === Description The {{json-abnf}} library contains procedures for parsing and printing JavaScript Object Notation (JSON) as described in [[https://www.rfc-editor.org/rfc/rfc8259|RFC 8259]]. It is intended to conform closely to the ABNF grammar in the RFC. A JSON value maps onto a plain Scheme value as follows: * {{true}} and {{false}} are Scheme {{#t}} and {{#f}} * {{null}} is the symbol {{'null}} * a JSON string is a Scheme string * a JSON number is a Scheme number * a JSON array is a Scheme vector * a JSON object is an association list of {{(key . value)}} pairs, {{key}} a string A complete JSON document can be any one of these -- an object, an array, a string, a number, {{true}}, {{false}}, or {{null}} -- optionally surrounded by whitespace, as RFC 8259 permits. (This is a relaxation from the older RFC 4627, which this library previously followed, and which required the outermost value to be an object or an array specifically.) See also [[json]] and [[medea]]. === Library Procedures <procedure>(parser TEXT) => VALUE</procedure><br> Parses {{TEXT}} as JSON, using the value mapping above, and returns the Scheme value it describes. On malformed input, prints an error message to the current output port and returns {{(error)}}. ==== Bidirectional printing: preliminaries The grammar in {{json-abnf}} is built with [[abnf]]'s {{abnf-lens}} component, which makes every rule bidirectional: the same rule declaration produces both the parser behind {{parser}} above and the printer behind {{printer}} below, so a value your program builds is guaranteed to print as text {{parser}} can read back in (see the [[abnf]] page for more on {{abnf-lens}} itself, including a step-by-step tutorial). <procedure>(printer VALUE) => STRING</procedure><br> Prints {{VALUE}} as JSON text, using the same value mapping described above -- {{VALUE}} can be any JSON value: an association list, a vector, a string, a number, {{#t}}, {{#f}}, or the symbol {{'null}}. On a value {{printer}} cannot print, prints an error message to the current output port and returns {{""}}. <enscript highlight="scheme"> (import json-abnf) (define person (list (cons "name" "Ada") (cons "tags" (vector "mathematician" "programmer")))) (printer person) ;; => "{\"name\":\"Ada\",\"tags\":[\"mathematician\",\"programmer\"]}" (parser (printer person)) ;; => (("name" . "Ada") ("tags" . #("mathematician" "programmer"))) ;; A document doesn't need to be an object or an array (parser "42") ;; => 42 (printer "hello") ;; => "\"hello\"" </enscript> ==== Bidirectional grammar rules The two rules below are what {{parser}} and {{printer}} are each built from ({{parser}} also accepts the narrower {{value}} shape internally; {{bi-text}} is the whole-document rule {{printer}} uses). They are exported directly, in case you want to embed the JSON grammar as part of a larger {{abnf-lens}} grammar. Each rule is a {{bp}} value, used with the {{bp-parse}} and {{bp-print}} procedures. Both the {{bp}} record and these two procedures are documented on the [[abnf]] page, along with {{bi-iso}}, {{bi-seq}}, and the other combinators the rules are built from. <procedure>bi-value => BP</procedure><br> The bidirectional counterpart of a JSON value: a {{bp}} whose parser reads any JSON value -- an object, an array, a string, a number, {{true}}, {{false}}, or {{null}} -- and whose printer writes any of those back out. Use it directly with {{bp-parse}} and {{bp-print}} when a value nested inside a larger structure, not a whole top-level document, is what needs parsing or printing. <procedure>bi-text => BP</procedure><br> The bidirectional counterpart of a whole JSON document: like {{bi-value}}, but also accepts optional surrounding whitespace, matching RFC 8259's rule for a complete JSON text ({{ws value ws}}). {{printer}} is {{bp-print}} applied to {{bi-text}}. <enscript highlight="scheme"> (import json-abnf abnf-lens) ;; bp-parse returns (list (list matched-value) remaining-stream); ;; (car (car ...)) unwraps it to the matched value. (car (car (bp-parse bi-text "[1,2,3]" (lambda (s) (error "parse failed" s))))) ;; => #(1 2 3) (bp-print bi-text (vector 1 2 3)) ;; => "[1,2,3]" </enscript> === Repository [[https://github.com/iraikov/chicken-json-abnf|https://github.com/iraikov/chicken-json-abnf]] === Requires * [[abnf]] === Version History * 7.0 Ported to CHICKEN 6; added {{abnf-lens}}-based bidirectional transforms. * 6.0 Using utf8 for char operations * 5.1 More bug fixes in parsing booleans [thanks to Vok Vojwo] * 5.0 Bug fixes in parsing booleans; using dotted lists for object representation [thanks to Vok Vojwo] * 4.0 Compatibility with abnf 5 * 3.2 Bug fixes in the parser for escaped characters; handling of empty vectors, objects, strings [thanks to Moritz Heidkamp] * 3.1 Updated version in setup file * 1.0 Initial Release === License Copyright 2009-2026 Ivan Raikov This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. A full copy of the GPL license can be found at <http://www.gnu.org/licenses/>. Description of your changes:

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