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-rw-r--r--src/guile/Makefile.am3
-rw-r--r--src/guile/skribilo/reader/gemtext.scm231
2 files changed, 233 insertions, 1 deletions
diff --git a/src/guile/Makefile.am b/src/guile/Makefile.am
index 98f2873..0a66a88 100644
--- a/src/guile/Makefile.am
+++ b/src/guile/Makefile.am
@@ -47,7 +47,8 @@ SOURCES = \
SOURCES += $(readers) $(packages) $(engines)
readers = \
- skribilo/reader/skribe.scm skribilo/reader/outline.scm
+ skribilo/reader/skribe.scm skribilo/reader/outline.scm \
+ skribilo/reader/gemtext.scm
if BUILD_RSS2_READER
diff --git a/src/guile/skribilo/reader/gemtext.scm b/src/guile/skribilo/reader/gemtext.scm
new file mode 100644
index 0000000..4ae403c
--- /dev/null
+++ b/src/guile/skribilo/reader/gemtext.scm
@@ -0,0 +1,231 @@
+;;; gemtext.scm -- A reader for the Gemini protocol's Gemtext markup
+;;;
+;;; Copyright © 2022 Arun Isaac <arunisaac@systemreboot.net>
+;;;
+;;;
+;;; This file is part of Skribilo.
+;;;
+;;; Skribilo 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.
+;;;
+;;; Skribilo 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.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Skribilo. If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (skribilo reader gemtext)
+ #:use-module (rnrs io ports)
+ #:use-module (srfi srfi-26)
+ #:use-module (srfi srfi-71)
+ #:use-module (srfi srfi-171)
+ #:use-module (ice-9 match)
+ #:use-module ((ice-9 textual-ports) #:select (unget-char unget-string))
+ #:use-module (skribilo reader)
+ #:use-module (skribilo utils syntax)
+ #:export (reader-specification
+ make-gemtext-reader))
+
+(skribilo-module-syntax)
+
+;;; Author: Arun Isaac
+;;;
+;;; Commentary:
+;;;
+;;; A reader for gemtext, the lightweight markup language used by the
+;;; Gemini protocol
+;;;
+;;; Code:
+
+(define %join-lines?
+ (make-parameter #f))
+
+(define %section-numbers?
+ (make-parameter #f))
+
+(define (string-blank? str)
+ "Return #t if STR contains only whitespace characters. Else, return
+#f."
+ (string-every char-set:whitespace str))
+
+(define (string-remove-prefix prefix str)
+ "Return STR with PREFIX removed. If PREFIX is not a prefix of STR,
+return #f."
+ (and (string-prefix? prefix str)
+ (substring str (string-length prefix))))
+
+(define (string-partition str char-pred)
+ "Return the part of STR before and after the first occurrence of
+CHAR-PRED as two values."
+ (let ((partition-index (string-index str char-pred)))
+ (if partition-index
+ (values (substring str 0 partition-index)
+ (substring str partition-index))
+ (values str #f))))
+
+(define (unget-line port line)
+ "Place the string LINE in PORT so that subsequent read operations
+will read LINE followed by a newline character."
+ (unget-char port #\newline)
+ (unget-string port line))
+
+(define (read-preformatted-text in out)
+ "Read preformatted text from port IN and write it to port OUT."
+ (let ((line (get-line in)))
+ (unless (or (eof-object? line)
+ (string-prefix? "```" line))
+ (put-string out line)
+ (newline out)
+ (read-preformatted-text in out))))
+
+(define (heading-level line)
+ "Return the level of the heading in LINE. If LINE is not a heading,
+return #f."
+ (cond
+ ((string-prefix? "### " line) 3)
+ ((string-prefix? "## " line) 2)
+ ((string-prefix? "# " line) 1)
+ (else #f)))
+
+(define (read-section-children level port)
+ "Read section elements of LEVEL from PORT. Return as a list."
+ (let ((line (get-line port)))
+ (cond
+ ;; End of file
+ ((eof-object? line) (list))
+ ;; If another heading of same or higher level begins, unget line
+ ;; and end section.
+ ((let ((heading-level (heading-level line)))
+ (and heading-level
+ (<= heading-level level)))
+ (unget-line port line)
+ (list))
+ ;; If blank line, continue.
+ ((string-blank? line)
+ (read-section-children level port))
+ ;; Else, add element and continue.
+ (else
+ (unget-line port line)
+ (cons (read-gemtext-element port)
+ (read-section-children level port))))))
+
+(define (paragraph-line? line)
+ "Return #t if LINE is a paragraph line. Else, return #f."
+ (not (or (string-blank? line)
+ (heading-level line)
+ (string-prefix? "* " line)
+ (string-prefix? ">" line)
+ (string-prefix? "=>" line)
+ (string-prefix? "```" line))))
+
+(define (link-line->ref line)
+ "Convert link LINE to a skribilo ref expression."
+ (let* ((trimmed-line (string-trim (string-remove-prefix "=>" line)))
+ (url text (string-partition trimmed-line (char-set #\space #\tab))))
+ (if text
+ `(ref #:url ,url #:text ,(string-trim text))
+ `(ref #:url ,url))))
+
+(define (retf-unget-line port result line)
+ "Unget LINE to PORT and return RESULT. This function is used as an
+argument to ttake-while."
+ (unget-line port line)
+ result)
+
+(define (read-gemtext-element port)
+ "Read next gemtext element from PORT."
+ (let ((line (get-line port)))
+ (cond
+ ;; End of file
+ ((eof-object? line) line)
+ ;; Section
+ ((heading-level line)
+ => (lambda (level)
+ `(,(case level
+ ((1) 'section)
+ ((2) 'subsection)
+ ((3) 'subsubsection))
+ #:title ,(substring line (1+ level))
+ #:number ,(%section-numbers?)
+ ,@(read-section-children level port))))
+ ;; List
+ ((string-remove-prefix "* " line)
+ => (lambda (first-item)
+ `(itemize
+ ,@(port-transduce (compose (ttake-while (cut string-prefix? "* " <>)
+ (cut retf-unget-line port <> <>))
+ (tmap (lambda (line)
+ `(item ,(string-remove-prefix "* " line)))))
+ rcons
+ (list `(item ,first-item))
+ get-line
+ port))))
+ ;; Blockquote
+ ((string-remove-prefix ">" line)
+ => (lambda (first-line)
+ (list 'blockquote
+ (if (%join-lines?)
+ (string-join
+ (port-transduce (compose (ttake-while (cut string-prefix? ">" <>)
+ (cut retf-unget-line port <> <>))
+ (tmap (cut string-remove-prefix ">" <>)))
+ rcons
+ (list first-line)
+ get-line
+ port)
+ " ")
+ line))))
+ ;; Link
+ ((string-prefix? "=>" line)
+ (cons 'paragraph
+ (port-transduce (compose (ttake-while (cut string-prefix? "=>" <>)
+ (cut retf-unget-line port <> <>))
+ (tmap link-line->ref))
+ rcons
+ (list (link-line->ref line))
+ get-line
+ port)))
+ ;; Preformatted text
+ ((string-remove-prefix "```" line)
+ => (lambda (alt-text)
+ ;; We don't use the alt text.
+ `(pre ,(call-with-output-string
+ (cut read-preformatted-text port <>)))))
+ ;; Ignore blank lines.
+ ((string-blank? line) (read-gemtext-element port))
+ ;; Paragraph
+ (else
+ (list 'paragraph
+ (if (%join-lines?)
+ (string-join
+ (port-transduce (ttake-while paragraph-line?
+ (cut retf-unget-line port <> <>))
+ rcons
+ (list line)
+ get-line
+ port)
+ " ")
+ line))))))
+
+(define* (make-gemtext-reader :key join-lines? section-numbers?)
+ "Return a gemtext reader.
+
+If JOIN-LINES? is #t, lines which are not separated by a blank line
+are joined into a single paragraph.
+
+If SECTION-NUMBERS? is #t, sections are numbered. Else, they are not."
+ (lambda (port)
+ (parameterize ((%join-lines? join-lines?)
+ (%section-numbers? section-numbers?))
+ (match (port-transduce (tmap identity)
+ rcons
+ read-gemtext-element
+ port)
+ (() (eof-object))
+ (elements `(document ,@elements))))))
+
+(define-reader gemtext "0.1" make-gemtext-reader)