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Article contents:== Outdated egg! This is an egg for CHICKEN 4, the unsupported old release. You're almost certainly looking for [[/eggref/5/abnf|the CHICKEN 5 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-5.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. [[tags: eggs]] [[toc:]] == abnf === Description {{abnf}} is a collection of combinators to help constructing parsers for Augmented Backus-Naur form (ABNF) grammars ([[http://www.ietf.org/rfc/rfc4234.txt|RFC 4234]]). === Library Procedures The combinator procedures in this library are based on the interface provided by the [[lexgen]] library. ==== {{<CoreABNF>}} typeclass The procedures of this library are provided as fields of the {{<CoreABNF>}} typeclass. Please see the [[typeclass]] library for information on type classes. The {{<CoreABNF>}} class is intended to provide abstraction over different kinds of input sequences, e.g. character lists, strings, streams, etc. The following example illustrates the creation of an instance of {{<CoreABNF>}} specialized for character lists. This code is also provided as the {{abnf-charlist}} egg, which is fully compatible with {{abnf}} prior to version 3.0. <enscript highlight="scheme"> (require-extension typeclass input-classes abnf) (define char-list-<Input> (make-<Input> null? car cdr)) (define char-list-<Token> (Input->Token char-list-<Input>)) (define char-list-<CharLex> (Token->CharLex char-list-<Token>)) (define char-list-<CoreABNF> (CharLex->CoreABNF char-list-<CharLex>)) (import-instance (<CoreABNF> char-list-<CoreABNF>)) </enscript> ==== Terminal values and core rules The following procedures are provided as fields in the {{<CoreABNF>}} typeclass: <procedure>(char CHAR) => MATCHER</procedure> Procedure {{char}} builds a pattern matcher function that matches a single character. <procedure>(lit STRING) => MATCHER</procedure> {{lit}} matches a literal string (case-insensitive). The following primitive parsers match the rules described in RFC 4234, Section 6.1. <procedure>(alpha STREAM-LIST) => STREAM-LIST</procedure> Matches any character of the alphabet. <procedure>(binary STREAM-LIST) => STREAM-LIST</procedure> Matches [0..1]. <procedure>(decimal STREAM-LIST) => STREAM-LIST</procedure> Matches [0..9]. <procedure>(hexadecimal STREAM-LIST) => STREAM-LIST</procedure> Matches [0..9] and [A..F,a..f]. <procedure>(ascii-char STREAM-LIST) => STREAM-LIST</procedure> Matches any 7-bit US-ASCII character except for NUL (ASCII value 0). <procedure>(cr STREAM-LIST) => STREAM-LIST</procedure> Matches the carriage return character. <procedure>(lf STREAM-LIST) => STREAM-LIST</procedure> Matches the line feed character. <procedure>(crlf STREAM-LIST) => STREAM-LIST</procedure> Matches the Internet newline. <procedure>(ctl STREAM-LIST) => STREAM-LIST</procedure> Matches any US-ASCII control character. That is, any character with a decimal value in the range of [0..31,127]. <procedure>(dquote STREAM-LIST) => STREAM-LIST</procedure> Matches the double quote character. <procedure>(htab STREAM-LIST) => STREAM-LIST</procedure> Matches the tab character. <procedure>(lwsp STREAM-LIST) => STREAM-LIST</procedure> Matches linear white-space. That is, any number of consecutive {{wsp}}, optionally followed by a {{crlf}} and (at least) one more {{wsp}}. <procedure>(sp STREAM-LIST) => STREAM-LIST</procedure> Matches the space character. <procedure>(vspace STREAM-LIST) => STREAM-LIST</procedure> Matches any printable ASCII character. That is, any character in the decimal range of [33..126]. <procedure>(wsp STREAM-LIST) => STREAM-LIST</procedure> Matches space or tab. <procedure>(quoted-pair STREAM-LIST) => STREAM-LIST</procedure> Matches a quoted pair. Any characters (excluding CR and LF) may be quoted. <procedure>(quoted-string STREAM-LIST) => STREAM-LIST</procedure> Matches a quoted string. The slash and double quote characters must be escaped inside a quoted string; CR and LF are not allowed at all. The following additional procedures are provided for convenience: <procedure>(set CHAR-SET) => MATCHER</procedure> Matches any character from an SRFI-14 character set. <procedure>(set-from-string STRING) => MATCHER</procedure> Matches any character from a set defined as a string. ==== Operators <procedure>(concatenation MATCHER-LIST) => MATCHER</procedure> {{concatenation}} matches an ordered list of rules. (RFC 4234, Section 3.1) <procedure>(alternatives MATCHER-LIST) => MATCHER</procedure> {{alternatives}} matches any one of the given list of rules. (RFC 4234, Section 3.2) <procedure>(range C1 C2) => MATCHER</procedure> {{range}} matches a range of characters. (RFC 4234, Section 3.4) <procedure>(variable-repetition MIN MAX MATCHER) => MATCHER</procedure> {{variable-repetition}} matches between {{MIN}} and {{MAX}} or more consecutive elements that match the given rule. (RFC 4234, Section 3.6) <procedure>(repetition MATCHER) => MATCHER</procedure> {{repetition}} matches zero or more consecutive elements that match the given rule. <procedure>(repetition1 MATCHER) => MATCHER</procedure> {{repetition1}} matches one or more consecutive elements that match the given rule. <procedure>(repetition-n N MATCHER) => MATCHER</procedure> {{repetition-n}} matches exactly {{N}} consecutive occurences of the given rule. (RFC 4234, Section 3.7) <procedure>(optional-sequence MATCHER) => MATCHER</procedure> {{optional-sequence}} matches the given optional rule. (RFC 4234, Section 3.8) <procedure>(pass) => MATCHER</procedure> This matcher returns without consuming any input. <procedure>(bind F P) => MATCHER</procedure> Given a rule {{P}} and function {{F}}, returns a matcher that first applies {{P}} to the input stream, then applies {{F}} to the returned list of consumed tokens, and returns the result and the remainder of the input stream. Note: this combinator will signal failure if the input stream is empty. <procedure>(bind* F P) => MATCHER</procedure> The same as {{bind}}, but will signal success if the input stream is empty. <procedure>(drop-consumed P) => MATCHER</procedure> Given a rule {{P}}, returns a matcher that always returns an empty list of consumed tokens when {{P}} succeeds. ==== Abbreviated syntax {{abnf}} supports the following abbreviations for commonly used combinators: ; {{::}} : {{concatenation}} ; {{:?}} : {{optional-sequence}} ; {{:!}} : {{drop-consumed}} ; {{:s}} : {{lit}} ; {{:c}} : {{char}} ; {{:*}} : {{repetition}} ; {{:+}} : {{repetition1}} === Examples The following parser libraries have been implemented with {{abnf}}, in order of complexity: * [[csv]] * [[internet-timestamp]] * [[json-abnf]] * [[mbox]] * [[smtp]] * [[internet-message]] * [[mime]] ==== Parsing date and time <enscript highlight="scheme"> (require-extension typeclass input-classes abnf) (define char-list-<Input> (make-<Input> null? car cdr)) (define char-list-<Token> (Input->Token char-list-<Input>)) (define char-list-<CharLex> (Token->CharLex char-list-<Token>)) (define char-list-<CoreABNF> (CharLex->CoreABNF char-list-<CharLex>)) (import-instance (<Token> char-list-<Token> char-list/) (<CharLex> char-list-<CharLex> char-list/) (<CoreABNF> char-list-<CoreABNF> char-list/) ) (define fws (concatenation (optional-sequence (concatenation (repetition char-list/wsp) (drop-consumed (alternatives char-list/crlf char-list/lf char-list/cr)))) (repetition1 char-list/wsp))) (define (between-fws p) (concatenation (drop-consumed (optional-sequence fws)) p (drop-consumed (optional-sequence fws)))) ;; Date and Time Specification from RFC 5322 (Internet Message Format) ;; The following abnf parser combinators parse a date and time ;; specification of the form ;; ;; Thu, 19 Dec 2002 20:35:46 +0200 ;; ; where the weekday specification is optional. ;; Match the abbreviated weekday names (define day-name (alternatives (char-list/lit "Mon") (char-list/lit "Tue") (char-list/lit "Wed") (char-list/lit "Thu") (char-list/lit "Fri") (char-list/lit "Sat") (char-list/lit "Sun"))) ;; Match a day-name, optionally wrapped in folding whitespace (define day-of-week (between-fws day-name)) ;; Match a four digit decimal number (define year (between-fws (repetition-n 4 char-list/decimal))) ;; Match the abbreviated month names (define month-name (alternatives (char-list/lit "Jan") (char-list/lit "Feb") (char-list/lit "Mar") (char-list/lit "Apr") (char-list/lit "May") (char-list/lit "Jun") (char-list/lit "Jul") (char-list/lit "Aug") (char-list/lit "Sep") (char-list/lit "Oct") (char-list/lit "Nov") (char-list/lit "Dec"))) ;; Match a month-name, optionally wrapped in folding whitespace (define month (between-fws month-name)) ;; Match a one or two digit number (define day (concatenation (drop-consumed (optional-sequence fws)) (alternatives (variable-repetition 1 2 char-list/decimal) (drop-consumed fws)))) ;; Match a date of the form dd:mm:yyyy (define date (concatenation day month year)) ;; Match a two-digit number (define hour (repetition-n 2 char-list/decimal)) (define minute (repetition-n 2 char-list/decimal)) (define isecond (repetition-n 2 char-list/decimal)) ;; Match a time-of-day specification of hh:mm or hh:mm:ss. (define time-of-day (concatenation hour (drop-consumed (char-list/char #\:)) minute (optional-sequence (concatenation (drop-consumed (char-list/char #\:)) isecond)))) ;; Match a timezone specification of the form ;; +hhmm or -hhmm (define zone (concatenation (drop-consumed fws) (alternatives (char-list/char #\-) (char-list/char #\+)) hour minute)) ;; Match a time-of-day specification followed by a zone. (define itime (concatenation time-of-day zone)) (define date-time (concatenation (optional-sequence (concatenation day-of-week (drop-consumed (char-list/char #\,)))) date itime (drop-consumed (optional-sequence fws)))) (define (err s) (print "lexical error on stream: " s) `(error)) (require-extension lexgen) (print (lex date-time err "Thu, 19 Dec 2002 20:35:46 +0200")) </enscript> === Requires * [[lexgen]] * [[typeclass]] * [[input-classes]] === Version History * 7.0 Added bind* variant of bind [thanks to Peter Bex] * 6.0 Using utf8 for char operations * 5.1 Improvements to the CharLex->CoreABNF constructor * 5.0 Synchronized with lexgen 5 * 3.2 Removed invalid identifier :| * 3.0 Implemented typeclass interface * 2.9 Bug fix in consumed-objects (reported by Peter Bex) * 2.7 Added abbreviated syntax (suggested by Moritz Heidkamp) * 2.6 Bug fixes in consumer procedures * 2.5 Removed procedure memo * 2.4 Moved the definition of bind and drop to lexgen * 2.2 Added pass combinator * 2.1 Added procedure variable-repetition * 2.0 Updated to match the interface of lexgen 2.0 * 1.3 Fix in drop * 1.2 Added procedures bind drop consume collect * 1.1 Added procedures set and set-from-string * 1.0 Initial release === License Copyright 2009-2015 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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