scanner.go

/*
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package candiedyaml

import (
	"bytes"
)

/*
 * Introduction
 * ************
 *
 * The following notes assume that you are familiar with the YAML specification
 * (http://yaml.org/spec/cvs/current.html).  We mostly follow it, although in
 * some cases we are less restrictive that it requires.
 *
 * The process of transforming a YAML stream into a sequence of events is
 * divided on two steps: Scanning and Parsing.
 *
 * The Scanner transforms the input stream into a sequence of tokens, while the
 * parser transform the sequence of tokens produced by the Scanner into a
 * sequence of parsing events.
 *
 * The Scanner is rather clever and complicated. The Parser, on the contrary,
 * is a straightforward implementation of a recursive-descendant parser (or,
 * LL(1) parser, as it is usually called).
 *
 * Actually there are two issues of Scanning that might be called "clever", the
 * rest is quite straightforward.  The issues are "block collection start" and
 * "simple keys".  Both issues are explained below in details.
 *
 * Here the Scanning step is explained and implemented.  We start with the list
 * of all the tokens produced by the Scanner together with short descriptions.
 *
 * Now, tokens:
 *
 *      STREAM-START(encoding)          # The stream start.
 *      STREAM-END                      # The stream end.
 *      VERSION-DIRECTIVE(major,minor)  # The '%YAML' directive.
 *      TAG-DIRECTIVE(handle,prefix)    # The '%TAG' directive.
 *      DOCUMENT-START                  # '---'
 *      DOCUMENT-END                    # '...'
 *      BLOCK-SEQUENCE-START            # Indentation increase denoting a block
 *      BLOCK-MAPPING-START             # sequence or a block mapping.
 *      BLOCK-END                       # Indentation decrease.
 *      FLOW-SEQUENCE-START             # '['
 *      FLOW-SEQUENCE-END               # ']'
 *      BLOCK-SEQUENCE-START            # '{'
 *      BLOCK-SEQUENCE-END              # '}'
 *      BLOCK-ENTRY                     # '-'
 *      FLOW-ENTRY                      # ','
 *      KEY                             # '?' or nothing (simple keys).
 *      VALUE                           # ':'
 *      ALIAS(anchor)                   # '*anchor'
 *      ANCHOR(anchor)                  # '&anchor'
 *      TAG(handle,suffix)              # '!handle!suffix'
 *      SCALAR(value,style)             # A scalar.
 *
 * The following two tokens are "virtual" tokens denoting the beginning and the
 * end of the stream:
 *
 *      STREAM-START(encoding)
 *      STREAM-END
 *
 * We pass the information about the input stream encoding with the
 * STREAM-START token.
 *
 * The next two tokens are responsible for tags:
 *
 *      VERSION-DIRECTIVE(major,minor)
 *      TAG-DIRECTIVE(handle,prefix)
 *
 * Example:
 *
 *      %YAML   1.1
 *      %TAG    !   !foo
 *      %TAG    !yaml!  tag:yaml.org,2002:
 *      ---
 *
 * The correspoding sequence of tokens:
 *
 *      STREAM-START(utf-8)
 *      VERSION-DIRECTIVE(1,1)
 *      TAG-DIRECTIVE("!","!foo")
 *      TAG-DIRECTIVE("!yaml","tag:yaml.org,2002:")
 *      DOCUMENT-START
 *      STREAM-END
 *
 * Note that the VERSION-DIRECTIVE and TAG-DIRECTIVE tokens occupy a whole
 * line.
 *
 * The document start and end indicators are represented by:
 *
 *      DOCUMENT-START
 *      DOCUMENT-END
 *
 * Note that if a YAML stream contains an implicit document (without '---'
 * and '...' indicators), no DOCUMENT-START and DOCUMENT-END tokens will be
 * produced.
 *
 * In the following examples, we present whole documents together with the
 * produced tokens.
 *
 *      1. An implicit document:
 *
 *          'a scalar'
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          SCALAR("a scalar",single-quoted)
 *          STREAM-END
 *
 *      2. An explicit document:
 *
 *          ---
 *          'a scalar'
 *          ...
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          DOCUMENT-START
 *          SCALAR("a scalar",single-quoted)
 *          DOCUMENT-END
 *          STREAM-END
 *
 *      3. Several documents in a stream:
 *
 *          'a scalar'
 *          ---
 *          'another scalar'
 *          ---
 *          'yet another scalar'
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          SCALAR("a scalar",single-quoted)
 *          DOCUMENT-START
 *          SCALAR("another scalar",single-quoted)
 *          DOCUMENT-START
 *          SCALAR("yet another scalar",single-quoted)
 *          STREAM-END
 *
 * We have already introduced the SCALAR token above.  The following tokens are
 * used to describe aliases, anchors, tag, and scalars:
 *
 *      ALIAS(anchor)
 *      ANCHOR(anchor)
 *      TAG(handle,suffix)
 *      SCALAR(value,style)
 *
 * The following series of examples illustrate the usage of these tokens:
 *
 *      1. A recursive sequence:
 *
 *          &A [ *A ]
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          ANCHOR("A")
 *          FLOW-SEQUENCE-START
 *          ALIAS("A")
 *          FLOW-SEQUENCE-END
 *          STREAM-END
 *
 *      2. A tagged scalar:
 *
 *          !!float "3.14"  # A good approximation.
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          TAG("!!","float")
 *          SCALAR("3.14",double-quoted)
 *          STREAM-END
 *
 *      3. Various scalar styles:
 *
 *          --- # Implicit empty plain scalars do not produce tokens.
 *          --- a plain scalar
 *          --- 'a single-quoted scalar'
 *          --- "a double-quoted scalar"
 *          --- |-
 *            a literal scalar
 *          --- >-
 *            a folded
 *            scalar
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          DOCUMENT-START
 *          DOCUMENT-START
 *          SCALAR("a plain scalar",plain)
 *          DOCUMENT-START
 *          SCALAR("a single-quoted scalar",single-quoted)
 *          DOCUMENT-START
 *          SCALAR("a double-quoted scalar",double-quoted)
 *          DOCUMENT-START
 *          SCALAR("a literal scalar",literal)
 *          DOCUMENT-START
 *          SCALAR("a folded scalar",folded)
 *          STREAM-END
 *
 * Now it's time to review collection-related tokens. We will start with
 * flow collections:
 *
 *      FLOW-SEQUENCE-START
 *      FLOW-SEQUENCE-END
 *      FLOW-MAPPING-START
 *      FLOW-MAPPING-END
 *      FLOW-ENTRY
 *      KEY
 *      VALUE
 *
 * The tokens FLOW-SEQUENCE-START, FLOW-SEQUENCE-END, FLOW-MAPPING-START, and
 * FLOW-MAPPING-END represent the indicators '[', ']', '{', and '}'
 * correspondingly.  FLOW-ENTRY represent the ',' indicator.  Finally the
 * indicators '?' and ':', which are used for denoting mapping keys and values,
 * are represented by the KEY and VALUE tokens.
 *
 * The following examples show flow collections:
 *
 *      1. A flow sequence:
 *
 *          [item 1, item 2, item 3]
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          FLOW-SEQUENCE-START
 *          SCALAR("item 1",plain)
 *          FLOW-ENTRY
 *          SCALAR("item 2",plain)
 *          FLOW-ENTRY
 *          SCALAR("item 3",plain)
 *          FLOW-SEQUENCE-END
 *          STREAM-END
 *
 *      2. A flow mapping:
 *
 *          {
 *              a simple key: a value,  # Note that the KEY token is produced.
 *              ? a complex key: another value,
 *          }
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          FLOW-MAPPING-START
 *          KEY
 *          SCALAR("a simple key",plain)
 *          VALUE
 *          SCALAR("a value",plain)
 *          FLOW-ENTRY
 *          KEY
 *          SCALAR("a complex key",plain)
 *          VALUE
 *          SCALAR("another value",plain)
 *          FLOW-ENTRY
 *          FLOW-MAPPING-END
 *          STREAM-END
 *
 * A simple key is a key which is not denoted by the '?' indicator.  Note that
 * the Scanner still produce the KEY token whenever it encounters a simple key.
 *
 * For scanning block collections, the following tokens are used (note that we
 * repeat KEY and VALUE here):
 *
 *      BLOCK-SEQUENCE-START
 *      BLOCK-MAPPING-START
 *      BLOCK-END
 *      BLOCK-ENTRY
 *      KEY
 *      VALUE
 *
 * The tokens BLOCK-SEQUENCE-START and BLOCK-MAPPING-START denote indentation
 * increase that precedes a block collection (cf. the INDENT token in Python).
 * The token BLOCK-END denote indentation decrease that ends a block collection
 * (cf. the DEDENT token in Python).  However YAML has some syntax pecularities
 * that makes detections of these tokens more complex.
 *
 * The tokens BLOCK-ENTRY, KEY, and VALUE are used to represent the indicators
 * '-', '?', and ':' correspondingly.
 *
 * The following examples show how the tokens BLOCK-SEQUENCE-START,
 * BLOCK-MAPPING-START, and BLOCK-END are emitted by the Scanner:
 *
 *      1. Block sequences:
 *
 *          - item 1
 *          - item 2
 *          -
 *            - item 3.1
 *            - item 3.2
 *          -
 *            key 1: value 1
 *            key 2: value 2
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          BLOCK-SEQUENCE-START
 *          BLOCK-ENTRY
 *          SCALAR("item 1",plain)
 *          BLOCK-ENTRY
 *          SCALAR("item 2",plain)
 *          BLOCK-ENTRY
 *          BLOCK-SEQUENCE-START
 *          BLOCK-ENTRY
 *          SCALAR("item 3.1",plain)
 *          BLOCK-ENTRY
 *          SCALAR("item 3.2",plain)
 *          BLOCK-END
 *          BLOCK-ENTRY
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("key 1",plain)
 *          VALUE
 *          SCALAR("value 1",plain)
 *          KEY
 *          SCALAR("key 2",plain)
 *          VALUE
 *          SCALAR("value 2",plain)
 *          BLOCK-END
 *          BLOCK-END
 *          STREAM-END
 *
 *      2. Block mappings:
 *
 *          a simple key: a value   # The KEY token is produced here.
 *          ? a complex key
 *          : another value
 *          a mapping:
 *            key 1: value 1
 *            key 2: value 2
 *          a sequence:
 *            - item 1
 *            - item 2
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("a simple key",plain)
 *          VALUE
 *          SCALAR("a value",plain)
 *          KEY
 *          SCALAR("a complex key",plain)
 *          VALUE
 *          SCALAR("another value",plain)
 *          KEY
 *          SCALAR("a mapping",plain)
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("key 1",plain)
 *          VALUE
 *          SCALAR("value 1",plain)
 *          KEY
 *          SCALAR("key 2",plain)
 *          VALUE
 *          SCALAR("value 2",plain)
 *          BLOCK-END
 *          KEY
 *          SCALAR("a sequence",plain)
 *          VALUE
 *          BLOCK-SEQUENCE-START
 *          BLOCK-ENTRY
 *          SCALAR("item 1",plain)
 *          BLOCK-ENTRY
 *          SCALAR("item 2",plain)
 *          BLOCK-END
 *          BLOCK-END
 *          STREAM-END
 *
 * YAML does not always require to start a new block collection from a new
 * line.  If the current line contains only '-', '?', and ':' indicators, a new
 * block collection may start at the current line.  The following examples
 * illustrate this case:
 *
 *      1. Collections in a sequence:
 *
 *          - - item 1
 *            - item 2
 *          - key 1: value 1
 *            key 2: value 2
 *          - ? complex key
 *            : complex value
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          BLOCK-SEQUENCE-START
 *          BLOCK-ENTRY
 *          BLOCK-SEQUENCE-START
 *          BLOCK-ENTRY
 *          SCALAR("item 1",plain)
 *          BLOCK-ENTRY
 *          SCALAR("item 2",plain)
 *          BLOCK-END
 *          BLOCK-ENTRY
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("key 1",plain)
 *          VALUE
 *          SCALAR("value 1",plain)
 *          KEY
 *          SCALAR("key 2",plain)
 *          VALUE
 *          SCALAR("value 2",plain)
 *          BLOCK-END
 *          BLOCK-ENTRY
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("complex key")
 *          VALUE
 *          SCALAR("complex value")
 *          BLOCK-END
 *          BLOCK-END
 *          STREAM-END
 *
 *      2. Collections in a mapping:
 *
 *          ? a sequence
 *          : - item 1
 *            - item 2
 *          ? a mapping
 *          : key 1: value 1
 *            key 2: value 2
 *
 *      Tokens:
 *
 *          STREAM-START(utf-8)
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("a sequence",plain)
 *          VALUE
 *          BLOCK-SEQUENCE-START
 *          BLOCK-ENTRY
 *          SCALAR("item 1",plain)
 *          BLOCK-ENTRY
 *          SCALAR("item 2",plain)
 *          BLOCK-END
 *          KEY
 *          SCALAR("a mapping",plain)
 *          VALUE
 *          BLOCK-MAPPING-START
 *          KEY
 *          SCALAR("key 1",plain)
 *          VALUE
 *          SCALAR("value 1",plain)
 *          KEY
 *          SCALAR("key 2",plain)
 *          VALUE
 *          SCALAR("value 2",plain)
 *          BLOCK-END
 *          BLOCK-END
 *          STREAM-END
 *
 * YAML also permits non-indented sequences if they are included into a block
 * mapping.  In this case, the token BLOCK-SEQUENCE-START is not produced:
 *
 *      key:
 *      - item 1    # BLOCK-SEQUENCE-START is NOT produced here.
 *      - item 2
 *
 * Tokens:
 *
 *      STREAM-START(utf-8)
 *      BLOCK-MAPPING-START
 *      KEY
 *      SCALAR("key",plain)
 *      VALUE
 *      BLOCK-ENTRY
 *      SCALAR("item 1",plain)
 *      BLOCK-ENTRY
 *      SCALAR("item 2",plain)
 *      BLOCK-END
 */

/*
 * Ensure that the buffer contains the required number of characters.
 * Return 1 on success, 0 on failure (reader error or memory error).
 */
func cache(parser *yaml_parser_t, length int) bool {
	if parser.unread >= length {
		return true
	}

	return yaml_parser_update_buffer(parser, length)
}

/*
 * Advance the buffer pointer.
 */
func skip(parser *yaml_parser_t) {
	parser.mark.index++
	parser.mark.column++
	parser.unread--
	parser.buffer_pos += width(parser.buffer[parser.buffer_pos])
}

func skip_line(parser *yaml_parser_t) {
	if is_crlf_at(parser.buffer, parser.buffer_pos) {
		parser.mark.index += 2
		parser.mark.column = 0
		parser.mark.line++
		parser.unread -= 2
		parser.buffer_pos += 2
	} else if is_break_at(parser.buffer, parser.buffer_pos) {
		parser.mark.index++
		parser.mark.column = 0
		parser.mark.line++
		parser.unread--
		parser.buffer_pos += width(parser.buffer[parser.buffer_pos])
	}
}

/*
 * Copy a character to a string buffer and advance pointers.
 */

func read(parser *yaml_parser_t, s []byte) []byte {
	w := width(parser.buffer[parser.buffer_pos])
	if w == 0 {
		panic("invalid character sequence")
	}
	if len(s) == 0 {
		s = make([]byte, 0, 32)
	}
	if w == 1 && len(s)+w <= cap(s) {
		s = s[:len(s)+1]
		s[len(s)-1] = parser.buffer[parser.buffer_pos]
		parser.buffer_pos++
	} else {
		s = append(s, parser.buffer[parser.buffer_pos:parser.buffer_pos+w]...)
		parser.buffer_pos += w
	}
	parser.mark.index++
	parser.mark.column++
	parser.unread--
	return s
}

/*
 * Copy a line break character to a string buffer and advance pointers.
 */
func read_line(parser *yaml_parser_t, s []byte) []byte {
	buf := parser.buffer
	pos := parser.buffer_pos
	if buf[pos] == '\r' && buf[pos+1] == '\n' {
		/* CR LF . LF */
		s = append(s, '\n')
		parser.buffer_pos += 2
		parser.mark.index++
		parser.unread--
	} else if buf[pos] == '\r' || buf[pos] == '\n' {
		/* CR|LF . LF */
		s = append(s, '\n')
		parser.buffer_pos += 1
	} else if buf[pos] == '\xC2' && buf[pos+1] == '\x85' {
		/* NEL . LF */
		s = append(s, '\n')
		parser.buffer_pos += 2
	} else if buf[pos] == '\xE2' && buf[pos+1] == '\x80' &&
		(buf[pos+2] == '\xA8' || buf[pos+2] == '\xA9') {
		// LS|PS . LS|PS
		s = append(s, buf[parser.buffer_pos:pos+3]...)
		parser.buffer_pos += 3
	} else {
		return s
	}

	parser.mark.index++
	parser.mark.column = 0
	parser.mark.line++
	parser.unread--
	return s
}

/*
 * Get the next token.
 */

func yaml_parser_scan(parser *yaml_parser_t, token *yaml_token_t) bool {
	/* Erase the token object. */
	*token = yaml_token_t{}

	/* No tokens after STREAM-END or error. */

	if parser.stream_end_produced || parser.error != yaml_NO_ERROR {
		return true
	}

	/* Ensure that the tokens queue contains enough tokens. */

	if !parser.token_available {
		if !yaml_parser_fetch_more_tokens(parser) {
			return false
		}
	}

	/* Fetch the next token from the queue. */

	*token = parser.tokens[parser.tokens_head]
	parser.tokens_head++
	parser.token_available = false
	parser.tokens_parsed++

	if token.token_type == yaml_STREAM_END_TOKEN {
		parser.stream_end_produced = true
	}

	return true
}

/*
 * Set the scanner error and return 0.
 */

func yaml_parser_set_scanner_error(parser *yaml_parser_t, context string,
	context_mark YAML_mark_t, problem string) bool {
	parser.error = yaml_SCANNER_ERROR
	parser.context = context
	parser.context_mark = context_mark
	parser.problem = problem
	parser.problem_mark = parser.mark

	return false
}

func yaml_parser_set_scanner_tag_error(parser *yaml_parser_t, directive bool, context_mark YAML_mark_t, problem string) bool {
	context := "while parsing a %TAG directive"
	if directive {
		context = "while parsing a tag"
	}
	return yaml_parser_set_scanner_error(parser, context, context_mark, "did not find URI escaped octet")
}

/*
 * Ensure that the tokens queue contains at least one token which can be
 * returned to the Parser.
 */

func yaml_parser_fetch_more_tokens(parser *yaml_parser_t) bool {
	/* While we need more tokens to fetch, do it. */

	for {
		/*
		 * Check if we really need to fetch more tokens.
		 */

		need_more_tokens := false

		if parser.tokens_head == len(parser.tokens) {
			/* Queue is empty. */

			need_more_tokens = true
		} else {

			/* Check if any potential simple key may occupy the head position. */

			if !yaml_parser_stale_simple_keys(parser) {
				return false
			}

			for i := range parser.simple_keys {
				simple_key := &parser.simple_keys[i]

				if simple_key.possible &&
					simple_key.token_number == parser.tokens_parsed {
					need_more_tokens = true
					break
				}
			}
		}
		if len(parser.simple_keys) > 0 {

		}
		/* We are finished. */

		if !need_more_tokens {
			break
		}

		/* Fetch the next token. */

		if !yaml_parser_fetch_next_token(parser) {
			return false
		}

	}

	parser.token_available = true

	return true
}

/*
 * The dispatcher for token fetchers.
 */

func yaml_parser_fetch_next_token(parser *yaml_parser_t) bool {
	/* Ensure that the buffer is initialized. */

	if !cache(parser, 1) {
		return false
	}

	/* Check if we just started scanning.  Fetch STREAM-START then. */

	if !parser.stream_start_produced {
		return yaml_parser_fetch_stream_start(parser)
	}

	/* Eat whitespaces and comments until we reach the next token. */

	if !yaml_parser_scan_to_next_token(parser) {
		return false
	}

	/* Remove obsolete potential simple keys. */

	if !yaml_parser_stale_simple_keys(parser) {
		return false
	}

	/* Check the indentation level against the current column. */

	if !yaml_parser_unroll_indent(parser, parser.mark.column) {
		return false
	}

	/*
	 * Ensure that the buffer contains at least 4 characters.  4 is the length
	 * of the longest indicators ('--- ' and '... ').
	 */

	if !cache(parser, 4) {
		return false
	}

	/* Is it the end of the stream? */
	buf := parser.buffer
	pos := parser.buffer_pos

	if is_z(buf[pos]) {
		return yaml_parser_fetch_stream_end(parser)
	}

	/* Is it a directive? */

	if parser.mark.column == 0 && buf[pos] == '%' {
		return yaml_parser_fetch_directive(parser)
	}

	/* Is it the document start indicator? */

	if parser.mark.column == 0 &&
		buf[pos] == '-' && buf[pos+1] == '-' && buf[pos+2] == '-' &&
		is_blankz_at(buf, pos+3) {
		return yaml_parser_fetch_document_indicator(parser,
			yaml_DOCUMENT_START_TOKEN)
	}

	/* Is it the document end indicator? */

	if parser.mark.column == 0 &&
		buf[pos] == '.' && buf[pos+1] == '.' && buf[pos+2] == '.' &&
		is_blankz_at(buf, pos+3) {
		return yaml_parser_fetch_document_indicator(parser,
			yaml_DOCUMENT_END_TOKEN)
	}

	/* Is it the flow sequence start indicator? */

	if buf[pos] == '[' {
		return yaml_parser_fetch_flow_collection_start(parser,
			yaml_FLOW_SEQUENCE_START_TOKEN)
	}

	/* Is it the flow mapping start indicator? */

	if buf[pos] == '{' {
		return yaml_parser_fetch_flow_collection_start(parser,
			yaml_FLOW_MAPPING_START_TOKEN)
	}

	/* Is it the flow sequence end indicator? */

	if buf[pos] == ']' {
		return yaml_parser_fetch_flow_collection_end(parser,
			yaml_FLOW_SEQUENCE_END_TOKEN)
	}

	/* Is it the flow mapping end indicator? */

	if buf[pos] == '}' {
		return yaml_parser_fetch_flow_collection_end(parser,
			yaml_FLOW_MAPPING_END_TOKEN)
	}

	/* Is it the flow entry indicator? */

	if buf[pos] == ',' {
		return yaml_parser_fetch_flow_entry(parser)
	}

	/* Is it the block entry indicator? */
	if buf[pos] == '-' && is_blankz_at(buf, pos+1) {
		return yaml_parser_fetch_block_entry(parser)
	}

	/* Is it the key indicator? */
	if buf[pos] == '?' &&
		(parser.flow_level > 0 || is_blankz_at(buf, pos+1)) {
		return yaml_parser_fetch_key(parser)
	}

	/* Is it the value indicator? */
	if buf[pos] == ':' &&
		(parser.flow_level > 0 || is_blankz_at(buf, pos+1)) {
		return yaml_parser_fetch_value(parser)
	}

	/* Is it an alias? */
	if buf[pos] == '*' {
		return yaml_parser_fetch_anchor(parser, yaml_ALIAS_TOKEN)
	}

	/* Is it an anchor? */

	if buf[pos] == '&' {
		return yaml_parser_fetch_anchor(parser, yaml_ANCHOR_TOKEN)
	}

	/* Is it a tag? */

	if buf[pos] == '!' {
		return yaml_parser_fetch_tag(parser)
	}

	/* Is it a literal scalar? */
	if buf[pos] == '|' && parser.flow_level == 0 {
		return yaml_parser_fetch_block_scalar(parser, true)
	}

	/* Is it a folded scalar? */
	if buf[pos] == '>' && parser.flow_level == 0 {
		return yaml_parser_fetch_block_scalar(parser, false)
	}

	/* Is it a single-quoted scalar? */

	if buf[pos] == '\'' {
		return yaml_parser_fetch_flow_scalar(parser, true)
	}

	/* Is it a double-quoted scalar? */
	if buf[pos] == '"' {
		return yaml_parser_fetch_flow_scalar(parser, false)
	}

	/*
	 * Is it a plain scalar?
	 *
	 * A plain scalar may start with any non-blank characters except
	 *
	 *      '-', '?', ':', ',', '[', ']', '{', '}',
	 *      '#', '&', '*', '!', '|', '>', '\'', '\"',
	 *      '%', '@', '`'.
	 *
	 * In the block context (and, for the '-' indicator, in the flow context
	 * too), it may also start with the characters
	 *
	 *      '-', '?', ':'
	 *
	 * if it is followed by a non-space character.
	 *
	 * The last rule is more restrictive than the specification requires.
	 */

	b := buf[pos]
	if !(is_blankz_at(buf, pos) || b == '-' ||
		b == '?' || b == ':' ||
		b == ',' || b == '[' ||
		b == ']' || b == '{' ||
		b == '}' || b == '#' ||
		b == '&' || b == '*' ||
		b == '!' || b == '|' ||
		b == '>' || b == '\'' ||
		b == '"' || b == '%' ||
		b == '@' || b == '`') ||
		(b == '-' && !is_blank(buf[pos+1])) ||
		(parser.flow_level == 0 &&
			(buf[pos] == '?' || buf[pos+1] == ':') &&
			!is_blank(buf[pos+1])) {
		return yaml_parser_fetch_plain_scalar(parser)
	}

	/*
	 * If we don't determine the token type so far, it is an error.
	 */

	return yaml_parser_set_scanner_error(parser,
		"while scanning for the next token", parser.mark,
		"found character that cannot start any token")
}

/*
 * Check the list of potential simple keys and remove the positions that
 * cannot contain simple keys anymore.
 */

func yaml_parser_stale_simple_keys(parser *yaml_parser_t) bool {
	/* Check for a potential simple key for each flow level. */

	for i := range parser.simple_keys {
		/*
		 * The specification requires that a simple key
		 *
		 *  - is limited to a single line,
		 *  - is shorter than 1024 characters.
		 */

		simple_key := &parser.simple_keys[i]
		if simple_key.possible &&
			(simple_key.mark.line < parser.mark.line ||
				simple_key.mark.index+1024 < parser.mark.index) {

			/* Check if the potential simple key to be removed is required. */

			if simple_key.required {
				return yaml_parser_set_scanner_error(parser,
					"while scanning a simple key", simple_key.mark,
					"could not find expected ':'")
			}

			simple_key.possible = false
		}
	}

	return true
}

/*
 * Check if a simple key may start at the current position and add it if
 * needed.
 */

func yaml_parser_save_simple_key(parser *yaml_parser_t) bool {
	/*
	 * A simple key is required at the current position if the scanner is in
	 * the block context and the current column coincides with the indentation
	 * level.
	 */

	required := (parser.flow_level == 0 &&
		parser.indent == parser.mark.column)

	/*
	 * A simple key is required only when it is the first token in the current
	 * line.  Therefore it is always allowed.  But we add a check anyway.
	 */
	if required && !parser.simple_key_allowed {
		panic("impossible") /* Impossible. */
	}

	/*
	 * If the current position may start a simple key, save it.
	 */

	if parser.simple_key_allowed {
		simple_key := yaml_simple_key_t{
			possible:     true,
			required:     required,
			token_number: parser.tokens_parsed + (len(parser.tokens) - parser.tokens_head),
		}
		simple_key.mark = parser.mark

		if !yaml_parser_remove_simple_key(parser) {
			return false
		}

		parser.simple_keys[len(parser.simple_keys)-1] = simple_key
	}

	return true
}

/*
 * Remove a potential simple key at the current flow level.
 */

func yaml_parser_remove_simple_key(parser *yaml_parser_t) bool {
	simple_key := &parser.simple_keys[len(parser.simple_keys)-1]

	if simple_key.possible {
		/* If the key is required, it is an error. */

		if simple_key.required {
			return yaml_parser_set_scanner_error(parser,
				"while scanning a simple key", simple_key.mark,
				"could not find expected ':'")
		}
	}

	/* Remove the key from the stack. */

	simple_key.possible = false

	return true
}

/*
 * Increase the flow level and resize the simple key list if needed.
 */

func yaml_parser_increase_flow_level(parser *yaml_parser_t) bool {
	/* Reset the simple key on the next level. */

	parser.simple_keys = append(parser.simple_keys, yaml_simple_key_t{})

	/* Increase the flow level. */

	parser.flow_level++

	return true
}

/*
 * Decrease the flow level.
 */

func yaml_parser_decrease_flow_level(parser *yaml_parser_t) bool {
	if parser.flow_level > 0 {
		parser.flow_level--
		parser.simple_keys = parser.simple_keys[:len(parser.simple_keys)-1]
	}

	return true
}

/*
 * Push the current indentation level to the stack and set the new level
 * the current column is greater than the indentation level.  In this case,
 * append or insert the specified token into the token queue.
 *
 */

func yaml_parser_roll_indent(parser *yaml_parser_t, column int,
	number int, token_type yaml_token_type_t, mark YAML_mark_t) bool {
	/* In the flow context, do nothing. */

	if parser.flow_level > 0 {
		return true
	}

	if parser.indent == -1 || parser.indent < column {
		/*
		 * Push the current indentation level to the stack and set the new
		 * indentation level.
		 */

		parser.indents = append(parser.indents, parser.indent)
		parser.indent = column

		/* Create a token and insert it into the queue. */
		token := yaml_token_t{
			token_type: token_type,
			start_mark: mark,
			end_mark:   mark,
		}

		// number == -1 -> enqueue otherwise insert
		if number > -1 {
			number -= parser.tokens_parsed
		}
		insert_token(parser, number, &token)
	}

	return true
}

/*
 * Pop indentation levels from the indents stack until the current level
 * becomes less or equal to the column.  For each indentation level, append
 * the BLOCK-END token.
 */

func yaml_parser_unroll_indent(parser *yaml_parser_t, column int) bool {
	/* In the flow context, do nothing. */

	if parser.flow_level > 0 {
		return true
	}

	/*
	 * column is unsigned and parser->indent is signed, so if
	 * parser->indent is less than zero the conditional in the while
	 * loop below is incorrect.  Guard against that.
	 */

	if parser.indent < 0 {
		return true
	}

	/* Loop through the indentation levels in the stack. */

	for parser.indent > column {
		/* Create a token and append it to the queue. */
		token := yaml_token_t{
			token_type: yaml_BLOCK_END_TOKEN,
			start_mark: parser.mark,
			end_mark:   parser.mark,
		}
		insert_token(parser, -1, &token)

		/* Pop the indentation level. */
		parser.indent = parser.indents[len(parser.indents)-1]
		parser.indents = parser.indents[:len(parser.indents)-1]

	}

	return true
}

/*
 * Pop indentation levels from the indents stack until the current
 * level resets to -1.  For each indentation level, append the
 * BLOCK-END token.
 */

func yaml_parser_reset_indent(parser *yaml_parser_t) bool {
	/* In the flow context, do nothing. */

	if parser.flow_level > 0 {
		return true
	}

	/* Loop through the indentation levels in the stack. */

	for parser.indent > -1 {
		/* Create a token and append it to the queue. */

		token := yaml_token_t{
			token_type: yaml_BLOCK_END_TOKEN,
			start_mark: parser.mark,
			end_mark:   parser.mark,
		}
		insert_token(parser, -1, &token)

		/* Pop the indentation level. */
		parser.indent = parser.indents[len(parser.indents)-1]
		parser.indents = parser.indents[:len(parser.indents)-1]
	}

	return true
}

/*
 * Initialize the scanner and produce the STREAM-START token.
 */

func yaml_parser_fetch_stream_start(parser *yaml_parser_t) bool {
	/* Set the initial indentation. */

	parser.indent = -1

	/* Initialize the simple key stack. */
	parser.simple_keys = append(parser.simple_keys, yaml_simple_key_t{})

	/* A simple key is allowed at the beginning of the stream. */

	parser.simple_key_allowed = true

	/* We have started. */

	parser.stream_start_produced = true

	/* Create the STREAM-START token and append it to the queue. */
	token := yaml_token_t{
		token_type: yaml_STREAM_START_TOKEN,
		start_mark: parser.mark,
		end_mark:   parser.mark,
		encoding:   parser.encoding,
	}
	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the STREAM-END token and shut down the scanner.
 */

func yaml_parser_fetch_stream_end(parser *yaml_parser_t) bool {
	/* Force new line. */

	if parser.mark.column != 0 {
		parser.mark.column = 0
		parser.mark.line++
	}

	/* Reset the indentation level. */

	if !yaml_parser_reset_indent(parser) {
		return false
	}

	/* Reset simple keys. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	parser.simple_key_allowed = false

	/* Create the STREAM-END token and append it to the queue. */
	token := yaml_token_t{
		token_type: yaml_STREAM_END_TOKEN,
		start_mark: parser.mark,
		end_mark:   parser.mark,
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce a VERSION-DIRECTIVE or TAG-DIRECTIVE token.
 */

func yaml_parser_fetch_directive(parser *yaml_parser_t) bool {
	/* Reset the indentation level. */

	if !yaml_parser_reset_indent(parser) {
		return false
	}

	/* Reset simple keys. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	parser.simple_key_allowed = false

	/* Create the YAML-DIRECTIVE or TAG-DIRECTIVE token. */
	var token yaml_token_t
	if !yaml_parser_scan_directive(parser, &token) {
		return false
	}

	/* Append the token to the queue. */
	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the DOCUMENT-START or DOCUMENT-END token.
 */

func yaml_parser_fetch_document_indicator(parser *yaml_parser_t,
	token_type yaml_token_type_t) bool {

	/* Reset the indentation level. */

	if !yaml_parser_reset_indent(parser) {
		return false
	}

	/* Reset simple keys. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	parser.simple_key_allowed = false

	/* Consume the token. */

	start_mark := parser.mark

	skip(parser)
	skip(parser)
	skip(parser)

	end_mark := parser.mark

	/* Create the DOCUMENT-START or DOCUMENT-END token. */

	token := yaml_token_t{
		token_type: token_type,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	/* Append the token to the queue. */

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the FLOW-SEQUENCE-START or FLOW-MAPPING-START token.
 */

func yaml_parser_fetch_flow_collection_start(parser *yaml_parser_t,
	token_type yaml_token_type_t) bool {

	/* The indicators '[' and '{' may start a simple key. */

	if !yaml_parser_save_simple_key(parser) {
		return false
	}

	/* Increase the flow level. */

	if !yaml_parser_increase_flow_level(parser) {
		return false
	}

	/* A simple key may follow the indicators '[' and '{'. */

	parser.simple_key_allowed = true

	/* Consume the token. */

	start_mark := parser.mark
	skip(parser)
	end_mark := parser.mark

	/* Create the FLOW-SEQUENCE-START of FLOW-MAPPING-START token. */

	token := yaml_token_t{
		token_type: token_type,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	/* Append the token to the queue. */

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the FLOW-SEQUENCE-END or FLOW-MAPPING-END token.
 */

func yaml_parser_fetch_flow_collection_end(parser *yaml_parser_t,
	token_type yaml_token_type_t) bool {

	/* Reset any potential simple key on the current flow level. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	/* Decrease the flow level. */

	if !yaml_parser_decrease_flow_level(parser) {
		return false
	}

	/* No simple keys after the indicators ']' and '}'. */

	parser.simple_key_allowed = false

	/* Consume the token. */

	start_mark := parser.mark
	skip(parser)
	end_mark := parser.mark

	/* Create the FLOW-SEQUENCE-END of FLOW-MAPPING-END token. */

	token := yaml_token_t{
		token_type: token_type,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	/* Append the token to the queue. */

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the FLOW-ENTRY token.
 */

func yaml_parser_fetch_flow_entry(parser *yaml_parser_t) bool {

	/* Reset any potential simple keys on the current flow level. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	/* Simple keys are allowed after ','. */

	parser.simple_key_allowed = true

	/* Consume the token. */

	start_mark := parser.mark
	skip(parser)
	end_mark := parser.mark

	/* Create the FLOW-ENTRY token and append it to the queue. */

	token := yaml_token_t{
		token_type: yaml_FLOW_ENTRY_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the BLOCK-ENTRY token.
 */

func yaml_parser_fetch_block_entry(parser *yaml_parser_t) bool {

	/* Check if the scanner is in the block context. */

	if parser.flow_level == 0 {
		/* Check if we are allowed to start a new entry. */

		if !parser.simple_key_allowed {
			return yaml_parser_set_scanner_error(parser, "", parser.mark,
				"block sequence entries are not allowed in this context")
		}

		/* Add the BLOCK-SEQUENCE-START token if needed. */

		if !yaml_parser_roll_indent(parser, parser.mark.column, -1,
			yaml_BLOCK_SEQUENCE_START_TOKEN, parser.mark) {
			return false
		}
	} else {
		/*
		 * It is an error for the '-' indicator to occur in the flow context,
		 * but we let the Parser detect and report about it because the Parser
		 * is able to point to the context.
		 */
	}

	/* Reset any potential simple keys on the current flow level. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	/* Simple keys are allowed after '-'. */

	parser.simple_key_allowed = true

	/* Consume the token. */

	start_mark := parser.mark
	skip(parser)
	end_mark := parser.mark

	/* Create the BLOCK-ENTRY token and append it to the queue. */

	token := yaml_token_t{
		token_type: yaml_BLOCK_ENTRY_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the KEY token.
 */

func yaml_parser_fetch_key(parser *yaml_parser_t) bool {
	/* In the block context, additional checks are required. */

	if parser.flow_level == 0 {
		/* Check if we are allowed to start a new key (not nessesary simple). */

		if !parser.simple_key_allowed {
			return yaml_parser_set_scanner_error(parser, "", parser.mark,
				"mapping keys are not allowed in this context")
		}

		/* Add the BLOCK-MAPPING-START token if needed. */

		if !yaml_parser_roll_indent(parser, parser.mark.column, -1,
			yaml_BLOCK_MAPPING_START_TOKEN, parser.mark) {
			return false
		}
	}

	/* Reset any potential simple keys on the current flow level. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	/* Simple keys are allowed after '?' in the block context. */

	parser.simple_key_allowed = (parser.flow_level == 0)

	/* Consume the token. */

	start_mark := parser.mark
	skip(parser)
	end_mark := parser.mark

	/* Create the KEY token and append it to the queue. */

	token := yaml_token_t{
		token_type: yaml_KEY_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the VALUE token.
 */

func yaml_parser_fetch_value(parser *yaml_parser_t) bool {

	simple_key := &parser.simple_keys[len(parser.simple_keys)-1]

	/* Have we found a simple key? */

	if simple_key.possible {

		/* Create the KEY token and insert it into the queue. */

		token := yaml_token_t{
			token_type: yaml_KEY_TOKEN,
			start_mark: simple_key.mark,
			end_mark:   simple_key.mark,
		}

		insert_token(parser, simple_key.token_number-parser.tokens_parsed, &token)

		/* In the block context, we may need to add the BLOCK-MAPPING-START token. */

		if !yaml_parser_roll_indent(parser, simple_key.mark.column,
			simple_key.token_number,
			yaml_BLOCK_MAPPING_START_TOKEN, simple_key.mark) {
			return false
		}

		/* Remove the simple key. */

		simple_key.possible = false

		/* A simple key cannot follow another simple key. */

		parser.simple_key_allowed = false
	} else {
		/* The ':' indicator follows a complex key. */

		/* In the block context, extra checks are required. */

		if parser.flow_level == 0 {
			/* Check if we are allowed to start a complex value. */

			if !parser.simple_key_allowed {
				return yaml_parser_set_scanner_error(parser, "", parser.mark,
					"mapping values are not allowed in this context")
			}

			/* Add the BLOCK-MAPPING-START token if needed. */

			if !yaml_parser_roll_indent(parser, parser.mark.column, -1,
				yaml_BLOCK_MAPPING_START_TOKEN, parser.mark) {
				return false
			}
		}

		/* Simple keys after ':' are allowed in the block context. */

		parser.simple_key_allowed = (parser.flow_level == 0)
	}

	/* Consume the token. */

	start_mark := parser.mark
	skip(parser)
	end_mark := parser.mark

	/* Create the VALUE token and append it to the queue. */

	token := yaml_token_t{
		token_type: yaml_VALUE_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the ALIAS or ANCHOR token.
 */

func yaml_parser_fetch_anchor(parser *yaml_parser_t, token_type yaml_token_type_t) bool {

	/* An anchor or an alias could be a simple key. */

	if !yaml_parser_save_simple_key(parser) {
		return false
	}

	/* A simple key cannot follow an anchor or an alias. */

	parser.simple_key_allowed = false

	/* Create the ALIAS or ANCHOR token and append it to the queue. */
	var token yaml_token_t
	if !yaml_parser_scan_anchor(parser, &token, token_type) {
		return false
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the TAG token.
 */

func yaml_parser_fetch_tag(parser *yaml_parser_t) bool {
	/* A tag could be a simple key. */

	if !yaml_parser_save_simple_key(parser) {
		return false
	}

	/* A simple key cannot follow a tag. */

	parser.simple_key_allowed = false

	/* Create the TAG token and append it to the queue. */
	var token yaml_token_t
	if !yaml_parser_scan_tag(parser, &token) {
		return false
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the SCALAR(...,literal) or SCALAR(...,folded) tokens.
 */

func yaml_parser_fetch_block_scalar(parser *yaml_parser_t, literal bool) bool {
	/* Remove any potential simple keys. */

	if !yaml_parser_remove_simple_key(parser) {
		return false
	}

	/* A simple key may follow a block scalar. */

	parser.simple_key_allowed = true

	/* Create the SCALAR token and append it to the queue. */
	var token yaml_token_t
	if !yaml_parser_scan_block_scalar(parser, &token, literal) {
		return false
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the SCALAR(...,single-quoted) or SCALAR(...,double-quoted) tokens.
 */

func yaml_parser_fetch_flow_scalar(parser *yaml_parser_t, single bool) bool {

	/* A plain scalar could be a simple key. */

	if !yaml_parser_save_simple_key(parser) {
		return false
	}

	/* A simple key cannot follow a flow scalar. */

	parser.simple_key_allowed = false

	/* Create the SCALAR token and append it to the queue. */
	var token yaml_token_t
	if !yaml_parser_scan_flow_scalar(parser, &token, single) {
		return false
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Produce the SCALAR(...,plain) token.
 */

func yaml_parser_fetch_plain_scalar(parser *yaml_parser_t) bool {
	/* A plain scalar could be a simple key. */

	if !yaml_parser_save_simple_key(parser) {
		return false
	}

	/* A simple key cannot follow a flow scalar. */

	parser.simple_key_allowed = false

	/* Create the SCALAR token and append it to the queue. */
	var token yaml_token_t
	if !yaml_parser_scan_plain_scalar(parser, &token) {
		return false
	}

	insert_token(parser, -1, &token)

	return true
}

/*
 * Eat whitespaces and comments until the next token is found.
 */

func yaml_parser_scan_to_next_token(parser *yaml_parser_t) bool {
	/* Until the next token is not found. */

	for {
		/* Allow the BOM mark to start a line. */

		if !cache(parser, 1) {
			return false
		}

		if parser.mark.column == 0 && is_bom_at(parser.buffer, parser.buffer_pos) {
			skip(parser)
		}

		/*
		 * Eat whitespaces.
		 *
		 * Tabs are allowed:
		 *
		 *  - in the flow context;
		 *  - in the block context, but not at the beginning of the line or
		 *  after '-', '?', or ':' (complex value).
		 */

		if !cache(parser, 1) {
			return false
		}

		for parser.buffer[parser.buffer_pos] == ' ' ||
			((parser.flow_level > 0 || !parser.simple_key_allowed) &&
				parser.buffer[parser.buffer_pos] == '\t') {
			skip(parser)
			if !cache(parser, 1) {
				return false
			}
		}

		/* Eat a comment until a line break. */

		if parser.buffer[parser.buffer_pos] == '#' {
			for !is_breakz_at(parser.buffer, parser.buffer_pos) {
				skip(parser)
				if !cache(parser, 1) {
					return false
				}
			}
		}

		/* If it is a line break, eat it. */

		if is_break_at(parser.buffer, parser.buffer_pos) {
			if !cache(parser, 2) {
				return false
			}
			skip_line(parser)

			/* In the block context, a new line may start a simple key. */

			if parser.flow_level == 0 {
				parser.simple_key_allowed = true
			}
		} else {
			/* We have found a token. */

			break
		}
	}

	return true
}

/*
 * Scan a YAML-DIRECTIVE or TAG-DIRECTIVE token.
 *
 * Scope:
 *      %YAML    1.1    # a comment \n
 *      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 *      %TAG    !yaml!  tag:yaml.org,2002:  \n
 *      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 */

func yaml_parser_scan_directive(parser *yaml_parser_t, token *yaml_token_t) bool {
	/* Eat '%'. */

	start_mark := parser.mark

	skip(parser)

	/* Scan the directive name. */
	var name []byte
	if !yaml_parser_scan_directive_name(parser, start_mark, &name) {
		return false
	}

	/* Is it a YAML directive? */
	var major, minor int
	if bytes.Equal(name, []byte("YAML")) {
		/* Scan the VERSION directive value. */

		if !yaml_parser_scan_version_directive_value(parser, start_mark,
			&major, &minor) {
			return false
		}

		end_mark := parser.mark

		/* Create a VERSION-DIRECTIVE token. */

		*token = yaml_token_t{
			token_type: yaml_VERSION_DIRECTIVE_TOKEN,
			start_mark: start_mark,
			end_mark:   end_mark,
			major:      major,
			minor:      minor,
		}
	} else if bytes.Equal(name, []byte("TAG")) {
		/* Is it a TAG directive? */
		/* Scan the TAG directive value. */
		var handle, prefix []byte
		if !yaml_parser_scan_tag_directive_value(parser, start_mark,
			&handle, &prefix) {
			return false
		}

		end_mark := parser.mark

		/* Create a TAG-DIRECTIVE token. */

		*token = yaml_token_t{
			token_type: yaml_TAG_DIRECTIVE_TOKEN,
			start_mark: start_mark,
			end_mark:   end_mark,
			value:      handle,
			prefix:     prefix,
		}
	} else {
		/* Unknown directive. */
		yaml_parser_set_scanner_error(parser, "while scanning a directive",
			start_mark, "found uknown directive name")
		return false
	}

	/* Eat the rest of the line including any comments. */

	if !cache(parser, 1) {
		return false
	}

	for is_blank(parser.buffer[parser.buffer_pos]) {
		skip(parser)
		if !cache(parser, 1) {
			return false
		}
	}

	if parser.buffer[parser.buffer_pos] == '#' {
		for !is_breakz_at(parser.buffer, parser.buffer_pos) {
			skip(parser)
			if !cache(parser, 1) {
				return false
			}
		}
	}

	/* Check if we are at the end of the line. */

	if !is_breakz_at(parser.buffer, parser.buffer_pos) {
		yaml_parser_set_scanner_error(parser, "while scanning a directive",
			start_mark, "did not find expected comment or line break")
		return false
	}

	/* Eat a line break. */

	if is_break_at(parser.buffer, parser.buffer_pos) {
		if !cache(parser, 2) {
			return false
		}
		skip_line(parser)
	}

	return true
}

/*
 * Scan the directive name.
 *
 * Scope:
 *      %YAML   1.1     # a comment \n
 *       ^^^^
 *      %TAG    !yaml!  tag:yaml.org,2002:  \n
 *       ^^^
 */

func yaml_parser_scan_directive_name(parser *yaml_parser_t,
	start_mark YAML_mark_t, name *[]byte) bool {

	/* Consume the directive name. */

	if !cache(parser, 1) {
		return false
	}

	var s []byte
	for is_alpha(parser.buffer[parser.buffer_pos]) {
		s = read(parser, s)
		if !cache(parser, 1) {
			return false
		}
	}

	/* Check if the name is empty. */

	if len(s) == 0 {
		yaml_parser_set_scanner_error(parser, "while scanning a directive",
			start_mark, "could not find expected directive name")
		return false
	}

	/* Check for an blank character after the name. */

	if !is_blankz_at(parser.buffer, parser.buffer_pos) {
		yaml_parser_set_scanner_error(parser, "while scanning a directive",
			start_mark, "found unexpected non-alphabetical character")
		return false
	}

	*name = s

	return true
}

/*
 * Scan the value of VERSION-DIRECTIVE.
 *
 * Scope:
 *      %YAML   1.1     # a comment \n
 *           ^^^^^^
 */

func yaml_parser_scan_version_directive_value(parser *yaml_parser_t,
	start_mark YAML_mark_t, major *int, minor *int) bool {
	/* Eat whitespaces. */

	if !cache(parser, 1) {
		return false
	}

	for is_blank(parser.buffer[parser.buffer_pos]) {
		skip(parser)
		if !cache(parser, 1) {
			return false
		}
	}

	/* Consume the major version number. */

	if !yaml_parser_scan_version_directive_number(parser, start_mark, major) {
		return false
	}

	/* Eat '.'. */

	if parser.buffer[parser.buffer_pos] != '.' {
		return yaml_parser_set_scanner_error(parser, "while scanning a %YAML directive",
			start_mark, "did not find expected digit or '.' character")
	}

	skip(parser)

	/* Consume the minor version number. */

	if !yaml_parser_scan_version_directive_number(parser, start_mark, minor) {
		return false
	}

	return true
}

const MAX_NUMBER_LENGTH = 9

/*
 * Scan the version number of VERSION-DIRECTIVE.
 *
 * Scope:
 *      %YAML   1.1     # a comment \n
 *              ^
 *      %YAML   1.1     # a comment \n
 *                ^
 */

func yaml_parser_scan_version_directive_number(parser *yaml_parser_t,
	start_mark YAML_mark_t, number *int) bool {

	/* Repeat while the next character is digit. */

	if !cache(parser, 1) {
		return false
	}

	value := 0
	length := 0
	for is_digit(parser.buffer[parser.buffer_pos]) {
		/* Check if the number is too long. */

		length++
		if length > MAX_NUMBER_LENGTH {
			return yaml_parser_set_scanner_error(parser, "while scanning a %YAML directive",
				start_mark, "found extremely long version number")
		}

		value = value*10 + as_digit(parser.buffer[parser.buffer_pos])

		skip(parser)

		if !cache(parser, 1) {
			return false
		}
	}

	/* Check if the number was present. */

	if length == 0 {
		return yaml_parser_set_scanner_error(parser, "while scanning a %YAML directive",
			start_mark, "did not find expected version number")
	}

	*number = value

	return true
}

/*
 * Scan the value of a TAG-DIRECTIVE token.
 *
 * Scope:
 *      %TAG    !yaml!  tag:yaml.org,2002:  \n
 *          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 */

func yaml_parser_scan_tag_directive_value(parser *yaml_parser_t,
	start_mark YAML_mark_t, handle, prefix *[]byte) bool {

	/* Eat whitespaces. */

	if !cache(parser, 1) {
		return false
	}

	for is_blank(parser.buffer[parser.buffer_pos]) {
		skip(parser)
		if !cache(parser, 1) {
			return false
		}
	}

	/* Scan a handle. */
	var handle_value []byte
	if !yaml_parser_scan_tag_handle(parser, true, start_mark, &handle_value) {
		return false
	}

	/* Expect a whitespace. */

	if !cache(parser, 1) {
		return false
	}

	if !is_blank(parser.buffer[parser.buffer_pos]) {
		yaml_parser_set_scanner_error(parser, "while scanning a %TAG directive",
			start_mark, "did not find expected whitespace")
		return false
	}

	/* Eat whitespaces. */

	for is_blank(parser.buffer[parser.buffer_pos]) {
		skip(parser)
		if !cache(parser, 1) {
			return false
		}
	}

	/* Scan a prefix. */
	var prefix_value []byte
	if !yaml_parser_scan_tag_uri(parser, true, nil, start_mark, &prefix_value) {
		return false
	}

	/* Expect a whitespace or line break. */

	if !cache(parser, 1) {
		return false
	}

	if !is_blankz_at(parser.buffer, parser.buffer_pos) {
		yaml_parser_set_scanner_error(parser, "while scanning a %TAG directive",
			start_mark, "did not find expected whitespace or line break")
		return false
	}

	*handle = handle_value
	*prefix = prefix_value

	return true
}

func yaml_parser_scan_anchor(parser *yaml_parser_t, token *yaml_token_t,
	token_type yaml_token_type_t) bool {

	/* Eat the indicator character. */

	start_mark := parser.mark

	skip(parser)

	/* Consume the value. */

	if !cache(parser, 1) {
		return false
	}

	var s []byte
	for is_alpha(parser.buffer[parser.buffer_pos]) {
		s = read(parser, s)
		if !cache(parser, 1) {
			return false
		}
	}

	end_mark := parser.mark

	/*
	 * Check if length of the anchor is greater than 0 and it is followed by
	 * a whitespace character or one of the indicators:
	 *
	 *      '?', ':', ',', ']', '}', '%', '@', '`'.
	 */

	b := parser.buffer[parser.buffer_pos]
	if len(s) == 0 || !(is_blankz_at(parser.buffer, parser.buffer_pos) || b == '?' ||
		b == ':' || b == ',' ||
		b == ']' || b == '}' ||
		b == '%' || b == '@' ||
		b == '`') {
		context := "while scanning an anchor"
		if token_type != yaml_ANCHOR_TOKEN {
			context = "while scanning an alias"
		}
		yaml_parser_set_scanner_error(parser, context, start_mark,
			"did not find expected alphabetic or numeric character")
		return false
	}

	/* Create a token. */
	*token = yaml_token_t{
		token_type: token_type,
		start_mark: start_mark,
		end_mark:   end_mark,
		value:      s,
	}

	return true
}

/*
 * Scan a TAG token.
 */

func yaml_parser_scan_tag(parser *yaml_parser_t, token *yaml_token_t) bool {
	start_mark := parser.mark

	/* Check if the tag is in the canonical form. */

	if !cache(parser, 2) {
		return false
	}

	var handle []byte
	var suffix []byte
	if parser.buffer[parser.buffer_pos+1] == '<' {
		/* Set the handle to '' */

		/* Eat '!<' */

		skip(parser)
		skip(parser)

		/* Consume the tag value. */

		if !yaml_parser_scan_tag_uri(parser, false, nil, start_mark, &suffix) {
			return false
		}

		/* Check for '>' and eat it. */

		if parser.buffer[parser.buffer_pos] != '>' {
			yaml_parser_set_scanner_error(parser, "while scanning a tag",
				start_mark, "did not find the expected '>'")
			return false
		}

		skip(parser)
	} else if is_blank(parser.buffer[parser.buffer_pos+1]) {
		// NON-SPECIFIED
		skip(parser)
	} else {
		/* The tag has either the '!suffix' or the '!handle!suffix' form. */

		/* First, try to scan a handle. */

		if !yaml_parser_scan_tag_handle(parser, false, start_mark, &handle) {
			return false
		}

		/* Check if it is, indeed, handle. */

		if handle[0] == '!' && len(handle) > 1 && handle[len(handle)-1] == '!' {
			/* Scan the suffix now. */

			if !yaml_parser_scan_tag_uri(parser, false, nil, start_mark, &suffix) {
				return false
			}
		} else {
			/* It wasn't a handle after all.  Scan the rest of the tag. */

			if !yaml_parser_scan_tag_uri(parser, false, handle, start_mark, &suffix) {
				return false
			}

			/* Set the handle to '!'. */

			handle = []byte{'!'}

			/*
			 * A special case: the '!' tag.  Set the handle to '' and the
			 * suffix to '!'.
			 */

			if len(suffix) == 0 {
				handle, suffix = suffix, handle
			}

		}
	}

	/* Check the character which ends the tag. */

	if !cache(parser, 1) {
		return false
	}

	if !is_blankz_at(parser.buffer, parser.buffer_pos) {
		yaml_parser_set_scanner_error(parser, "while scanning a tag",
			start_mark, "did not find expected whitespace or line break")
		return false
	}

	end_mark := parser.mark

	/* Create a token. */

	*token = yaml_token_t{
		token_type: yaml_TAG_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
		value:      handle,
		suffix:     suffix,
	}

	return true
}

/*
 * Scan a tag handle.
 */

func yaml_parser_scan_tag_handle(parser *yaml_parser_t, directive bool,
	start_mark YAML_mark_t, handle *[]byte) bool {

	/* Check the initial '!' character. */

	if !cache(parser, 1) {
		return false
	}

	if parser.buffer[parser.buffer_pos] != '!' {
		yaml_parser_set_scanner_tag_error(parser, directive,
			start_mark, "did not find expected '!'")
		return false
	}

	/* Copy the '!' character. */
	var s []byte
	s = read(parser, s)

	/* Copy all subsequent alphabetical and numerical characters. */

	if !cache(parser, 1) {
		return false
	}

	for is_alpha(parser.buffer[parser.buffer_pos]) {
		s = read(parser, s)
		if !cache(parser, 1) {
			return false
		}
	}

	/* Check if the trailing character is '!' and copy it. */

	if parser.buffer[parser.buffer_pos] == '!' {
		s = read(parser, s)
	} else {
		/*
		 * It's either the '!' tag or not really a tag handle.  If it's a %TAG
		 * directive, it's an error.  If it's a tag token, it must be a part of
		 * URI.
		 */

		if directive && !(s[0] == '!' && len(s) == 1) {
			yaml_parser_set_scanner_tag_error(parser, directive,
				start_mark, "did not find expected '!'")
			return false
		}
	}

	*handle = s

	return true
}

/*
 * Scan a tag.
 */

func yaml_parser_scan_tag_uri(parser *yaml_parser_t, directive bool,
	head []byte, start_mark YAML_mark_t, uri *[]byte) bool {

	var s []byte
	/*
	 * Copy the head if needed.
	 *
	 * Note that we don't copy the leading '!' character.
	 */
	if len(head) > 1 {
		s = append(s, head[1:]...)
	}

	/* Scan the tag. */
	if !cache(parser, 1) {
		return false
	}

	/*
	 * The set of characters that may appear in URI is as follows:
	 *
	 *      '0'-'9', 'A'-'Z', 'a'-'z', '_', '-', ';', '/', '?', ':', '@', '&',
	 *      '=', '+', '$', ',', '.', '!', '~', '*', '\'', '(', ')', '[', ']',
	 *      '%'.
	 */

	b := parser.buffer[parser.buffer_pos]
	for is_alpha(b) || b == ';' ||
		b == '/' || b == '?' ||
		b == ':' || b == '@' ||
		b == '&' || b == '=' ||
		b == '+' || b == '$' ||
		b == ',' || b == '.' ||
		b == '!' || b == '~' ||
		b == '*' || b == '\'' ||
		b == '(' || b == ')' ||
		b == '[' || b == ']' ||
		b == '%' {
		/* Check if it is a URI-escape sequence. */

		if b == '%' {
			if !yaml_parser_scan_uri_escapes(parser,
				directive, start_mark, &s) {
				return false
			}
		} else {
			s = read(parser, s)
		}

		if !cache(parser, 1) {
			return false
		}
		b = parser.buffer[parser.buffer_pos]
	}

	/* Check if the tag is non-empty. */

	if len(s) == 0 {
		yaml_parser_set_scanner_tag_error(parser, directive,
			start_mark, "did not find expected tag URI")
		return false
	}

	*uri = s

	return true
}

/*
 * Decode an URI-escape sequence corresponding to a single UTF-8 character.
 */

func yaml_parser_scan_uri_escapes(parser *yaml_parser_t, directive bool,
	start_mark YAML_mark_t, s *[]byte) bool {

	/* Decode the required number of characters. */
	w := 10
	for w > 0 {

		/* Check for a URI-escaped octet. */

		if !cache(parser, 3) {
			return false
		}

		if !(parser.buffer[parser.buffer_pos] == '%' &&
			is_hex(parser.buffer[parser.buffer_pos+1]) &&
			is_hex(parser.buffer[parser.buffer_pos+2])) {
			return yaml_parser_set_scanner_tag_error(parser, directive,
				start_mark, "did not find URI escaped octet")
		}

		/* Get the octet. */
		octet := byte((as_hex(parser.buffer[parser.buffer_pos+1]) << 4) +
			as_hex(parser.buffer[parser.buffer_pos+2]))

		/* If it is the leading octet, determine the length of the UTF-8 sequence. */

		if w == 10 {
			w = width(octet)
			if w == 0 {
				return yaml_parser_set_scanner_tag_error(parser, directive,
					start_mark, "found an incorrect leading UTF-8 octet")
			}
		} else {
			/* Check if the trailing octet is correct. */

			if (octet & 0xC0) != 0x80 {
				return yaml_parser_set_scanner_tag_error(parser, directive,
					start_mark, "found an incorrect trailing UTF-8 octet")
			}
		}

		/* Copy the octet and move the pointers. */

		*s = append(*s, octet)
		skip(parser)
		skip(parser)
		skip(parser)
		w--
	}

	return true
}

/*
 * Scan a block scalar.
 */

func yaml_parser_scan_block_scalar(parser *yaml_parser_t, token *yaml_token_t,
	literal bool) bool {

	/* Eat the indicator '|' or '>'. */

	start_mark := parser.mark

	skip(parser)

	/* Scan the additional block scalar indicators. */

	if !cache(parser, 1) {
		return false
	}

	/* Check for a chomping indicator. */
	chomping := 0
	increment := 0
	if parser.buffer[parser.buffer_pos] == '+' || parser.buffer[parser.buffer_pos] == '-' {
		/* Set the chomping method and eat the indicator. */

		if parser.buffer[parser.buffer_pos] == '+' {
			chomping = +1
		} else {
			chomping = -1
		}

		skip(parser)

		/* Check for an indentation indicator. */

		if !cache(parser, 1) {
			return false
		}

		if is_digit(parser.buffer[parser.buffer_pos]) {
			/* Check that the indentation is greater than 0. */

			if parser.buffer[parser.buffer_pos] == '0' {
				yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
					start_mark, "found an indentation indicator equal to 0")
				return false
			}

			/* Get the indentation level and eat the indicator. */

			increment = as_digit(parser.buffer[parser.buffer_pos])

			skip(parser)
		}
	} else if is_digit(parser.buffer[parser.buffer_pos]) {

		/* Do the same as above, but in the opposite order. */
		if parser.buffer[parser.buffer_pos] == '0' {
			yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
				start_mark, "found an indentation indicator equal to 0")
			return false
		}

		increment = as_digit(parser.buffer[parser.buffer_pos])

		skip(parser)

		if !cache(parser, 1) {
			return false
		}

		if parser.buffer[parser.buffer_pos] == '+' || parser.buffer[parser.buffer_pos] == '-' {
			if parser.buffer[parser.buffer_pos] == '+' {
				chomping = +1
			} else {
				chomping = -1
			}

			skip(parser)
		}
	}

	/* Eat whitespaces and comments to the end of the line. */

	if !cache(parser, 1) {
		return false
	}

	for is_blank(parser.buffer[parser.buffer_pos]) {
		skip(parser)
		if !cache(parser, 1) {
			return false
		}
	}

	if parser.buffer[parser.buffer_pos] == '#' {
		for !is_breakz_at(parser.buffer, parser.buffer_pos) {
			skip(parser)
			if !cache(parser, 1) {
				return false
			}
		}
	}

	/* Check if we are at the end of the line. */

	if !is_breakz_at(parser.buffer, parser.buffer_pos) {
		yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
			start_mark, "did not find expected comment or line break")
		return false
	}

	/* Eat a line break. */

	if is_break_at(parser.buffer, parser.buffer_pos) {
		if !cache(parser, 2) {
			return false
		}

		skip_line(parser)
	}

	end_mark := parser.mark

	/* Set the indentation level if it was specified. */
	indent := 0
	if increment > 0 {
		if parser.indent >= 0 {
			indent = parser.indent + increment
		} else {
			indent = increment
		}
	}

	/* Scan the leading line breaks and determine the indentation level if needed. */
	var trailing_breaks []byte
	if !yaml_parser_scan_block_scalar_breaks(parser, &indent, &trailing_breaks,
		start_mark, &end_mark) {
		return false
	}

	/* Scan the block scalar content. */

	if !cache(parser, 1) {
		return false
	}

	var s []byte
	var leading_break []byte
	leading_blank := false
	trailing_blank := false
	for parser.mark.column == indent && !is_z(parser.buffer[parser.buffer_pos]) {

		/*
		 * We are at the beginning of a non-empty line.
		 */

		/* Is it a trailing whitespace? */

		trailing_blank = is_blank(parser.buffer[parser.buffer_pos])

		/* Check if we need to fold the leading line break. */

		if !literal && len(leading_break) > 0 && leading_break[0] == '\n' &&
			!leading_blank && !trailing_blank {
			/* Do we need to join the lines by space? */
			if len(trailing_breaks) == 0 {
				s = append(s, ' ')
			}
			leading_break = leading_break[:0]
		} else {
			s = append(s, leading_break...)
			leading_break = leading_break[:0]
		}

		/* Append the remaining line breaks. */
		s = append(s, trailing_breaks...)
		trailing_breaks = trailing_breaks[:0]

		/* Is it a leading whitespace? */

		leading_blank = is_blank(parser.buffer[parser.buffer_pos])

		/* Consume the current line. */

		for !is_breakz_at(parser.buffer, parser.buffer_pos) {
			s = read(parser, s)
			if !cache(parser, 1) {
				return false
			}
		}

		/* Consume the line break. */

		if !cache(parser, 2) {
			return false
		}

		leading_break = read_line(parser, leading_break)

		/* Eat the following indentation spaces and line breaks. */

		if !yaml_parser_scan_block_scalar_breaks(parser,
			&indent, &trailing_breaks, start_mark, &end_mark) {
			return false
		}
	}

	/* Chomp the tail. */

	if chomping != -1 {
		s = append(s, leading_break...)
	}
	if chomping == 1 {
		s = append(s, trailing_breaks...)
	}

	/* Create a token. */

	*token = yaml_token_t{
		token_type: yaml_SCALAR_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
		value:      s,
		style:      yaml_LITERAL_SCALAR_STYLE,
	}
	if !literal {
		token.style = yaml_FOLDED_SCALAR_STYLE
	}

	return true
}

/*
 * Scan indentation spaces and line breaks for a block scalar.  Determine the
 * indentation level if needed.
 */

func yaml_parser_scan_block_scalar_breaks(parser *yaml_parser_t,
	indent *int, breaks *[]byte,
	start_mark YAML_mark_t, end_mark *YAML_mark_t) bool {

	*end_mark = parser.mark

	/* Eat the indentation spaces and line breaks. */
	max_indent := 0
	for {
		/* Eat the indentation spaces. */

		if !cache(parser, 1) {
			return false
		}

		for (*indent == 0 || parser.mark.column < *indent) &&
			is_space(parser.buffer[parser.buffer_pos]) {
			skip(parser)
			if !cache(parser, 1) {
				return false
			}
		}
		if parser.mark.column > max_indent {
			max_indent = parser.mark.column
		}

		/* Check for a tab character messing the indentation. */

		if (*indent == 0 || parser.mark.column < *indent) &&
			is_tab(parser.buffer[parser.buffer_pos]) {
			return yaml_parser_set_scanner_error(parser, "while scanning a block scalar",
				start_mark, "found a tab character where an indentation space is expected")
		}

		/* Have we found a non-empty line? */

		if !is_break_at(parser.buffer, parser.buffer_pos) {
			break
		}

		/* Consume the line break. */

		if !cache(parser, 2) {
			return false
		}

		*breaks = read_line(parser, *breaks)
		*end_mark = parser.mark
	}

	/* Determine the indentation level if needed. */

	if *indent == 0 {
		*indent = max_indent
		if *indent < parser.indent+1 {
			*indent = parser.indent + 1
		}
		if *indent < 1 {
			*indent = 1
		}
	}

	return true
}

/*
 * Scan a quoted scalar.
 */

func yaml_parser_scan_flow_scalar(parser *yaml_parser_t, token *yaml_token_t,
	single bool) bool {

	/* Eat the left quote. */

	start_mark := parser.mark

	skip(parser)

	/* Consume the content of the quoted scalar. */
	var s []byte
	var leading_break []byte
	var trailing_breaks []byte
	var whitespaces []byte
	for {
		/* Check that there are no document indicators at the beginning of the line. */

		if !cache(parser, 4) {
			return false
		}

		if parser.mark.column == 0 &&
			((parser.buffer[parser.buffer_pos] == '-' &&
				parser.buffer[parser.buffer_pos+1] == '-' &&
				parser.buffer[parser.buffer_pos+2] == '-') ||
				(parser.buffer[parser.buffer_pos] == '.' &&
					parser.buffer[parser.buffer_pos+1] == '.' &&
					parser.buffer[parser.buffer_pos+2] == '.')) &&
			is_blankz_at(parser.buffer, parser.buffer_pos+3) {
			yaml_parser_set_scanner_error(parser, "while scanning a quoted scalar",
				start_mark, "found unexpected document indicator")
			return false
		}

		/* Check for EOF. */

		if is_z(parser.buffer[parser.buffer_pos]) {
			yaml_parser_set_scanner_error(parser, "while scanning a quoted scalar",
				start_mark, "found unexpected end of stream")
			return false
		}

		/* Consume non-blank characters. */

		if !cache(parser, 2) {
			return false
		}

		leading_blanks := false

		for !is_blankz_at(parser.buffer, parser.buffer_pos) {
			/* Check for an escaped single quote. */

			if single && parser.buffer[parser.buffer_pos] == '\'' &&
				parser.buffer[parser.buffer_pos+1] == '\'' {
				// Is is an escaped single quote.
				s = append(s, '\'')
				skip(parser)
				skip(parser)
			} else if single && parser.buffer[parser.buffer_pos] == '\'' {
				/* Check for the right quote. */
				break
			} else if !single && parser.buffer[parser.buffer_pos] == '"' {
				/* Check for the right quote. */
				break
			} else if !single && parser.buffer[parser.buffer_pos] == '\\' &&
				is_break_at(parser.buffer, parser.buffer_pos+1) {

				/* Check for an escaped line break. */
				if !cache(parser, 3) {
					return false
				}

				skip(parser)
				skip_line(parser)
				leading_blanks = true
				break
			} else if !single && parser.buffer[parser.buffer_pos] == '\\' {

				/* Check for an escape sequence. */

				code_length := 0

				/* Check the escape character. */

				switch parser.buffer[parser.buffer_pos+1] {
				case '0':
					s = append(s, 0)
				case 'a':
					s = append(s, '\x07')
				case 'b':
					s = append(s, '\x08')
				case 't', '\t':
					s = append(s, '\x09')
				case 'n':
					s = append(s, '\x0A')
				case 'v':
					s = append(s, '\x0B')
				case 'f':
					s = append(s, '\x0C')
				case 'r':
					s = append(s, '\x0D')
				case 'e':
					s = append(s, '\x1B')
				case ' ':
					s = append(s, '\x20')
				case '"':
					s = append(s, '"')
				case '/':
					s = append(s, '/')
				case '\\':
					s = append(s, '\\')
				case 'N': /* NEL (#x85) */
					s = append(s, '\xC2')
					s = append(s, '\x85')
				case '_': /* #xA0 */
					s = append(s, '\xC2')
					s = append(s, '\xA0')
				case 'L': /* LS (#x2028) */
					s = append(s, '\xE2')
					s = append(s, '\x80')
					s = append(s, '\xA8')
				case 'P': /* PS (#x2029) */
					s = append(s, '\xE2')
					s = append(s, '\x80')
					s = append(s, '\xA9')
				case 'x':
					code_length = 2
				case 'u':
					code_length = 4
				case 'U':
					code_length = 8
				default:
					yaml_parser_set_scanner_error(parser, "while parsing a quoted scalar",
						start_mark, "found unknown escape character")
					return false
				}

				skip(parser)
				skip(parser)

				/* Consume an arbitrary escape code. */

				if code_length > 0 {
					value := 0

					/* Scan the character value. */

					if !cache(parser, code_length) {
						return false
					}

					for k := 0; k < code_length; k++ {
						if !is_hex(parser.buffer[parser.buffer_pos+k]) {
							yaml_parser_set_scanner_error(parser, "while parsing a quoted scalar",
								start_mark, "did not find expected hexdecimal number")
							return false
						}
						value = (value << 4) + as_hex(parser.buffer[parser.buffer_pos+k])
					}

					/* Check the value and write the character. */

					if (value >= 0xD800 && value <= 0xDFFF) || value > 0x10FFFF {
						yaml_parser_set_scanner_error(parser, "while parsing a quoted scalar",
							start_mark, "found invalid Unicode character escape code")
						return false
					}

					if value <= 0x7F {
						s = append(s, byte(value))
					} else if value <= 0x7FF {
						s = append(s, byte(0xC0+(value>>6)))
						s = append(s, byte(0x80+(value&0x3F)))
					} else if value <= 0xFFFF {
						s = append(s, byte(0xE0+(value>>12)))
						s = append(s, byte(0x80+((value>>6)&0x3F)))
						s = append(s, byte(0x80+(value&0x3F)))
					} else {
						s = append(s, byte(0xF0+(value>>18)))
						s = append(s, byte(0x80+((value>>12)&0x3F)))
						s = append(s, byte(0x80+((value>>6)&0x3F)))
						s = append(s, byte(0x80+(value&0x3F)))
					}

					/* Advance the pointer. */

					for k := 0; k < code_length; k++ {
						skip(parser)
					}
				}
			} else {
				/* It is a non-escaped non-blank character. */

				s = read(parser, s)
			}

			if !cache(parser, 2) {
				return false
			}
		}

		/* Check if we are at the end of the scalar. */
		b := parser.buffer[parser.buffer_pos]
		if single {
			if b == '\'' {
				break
			}
		} else if b == '"' {
			break
		}

		/* Consume blank characters. */

		if !cache(parser, 1) {
			return false
		}

		for is_blank(parser.buffer[parser.buffer_pos]) || is_break_at(parser.buffer, parser.buffer_pos) {
			if is_blank(parser.buffer[parser.buffer_pos]) {
				/* Consume a space or a tab character. */
				if !leading_blanks {
					whitespaces = read(parser, whitespaces)
				} else {
					skip(parser)
				}
			} else {
				if !cache(parser, 2) {
					return false
				}

				/* Check if it is a first line break. */
				if !leading_blanks {
					whitespaces = whitespaces[:0]
					leading_break = read_line(parser, leading_break)
					leading_blanks = true
				} else {
					trailing_breaks = read_line(parser, trailing_breaks)
				}
			}

			if !cache(parser, 1) {
				return false
			}
		}

		/* Join the whitespaces or fold line breaks. */

		if leading_blanks {
			/* Do we need to fold line breaks? */

			if len(leading_break) > 0 && leading_break[0] == '\n' {
				if len(trailing_breaks) == 0 {
					s = append(s, ' ')
				} else {
					s = append(s, trailing_breaks...)
					trailing_breaks = trailing_breaks[:0]
				}

				leading_break = leading_break[:0]
			} else {
				s = append(s, leading_break...)
				s = append(s, trailing_breaks...)
				leading_break = leading_break[:0]
				trailing_breaks = trailing_breaks[:0]
			}
		} else {
			s = append(s, whitespaces...)
			whitespaces = whitespaces[:0]
		}
	}

	/* Eat the right quote. */

	skip(parser)

	end_mark := parser.mark

	/* Create a token. */

	*token = yaml_token_t{
		token_type: yaml_SCALAR_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
		value:      s,
		style:      yaml_SINGLE_QUOTED_SCALAR_STYLE,
	}
	if !single {
		token.style = yaml_DOUBLE_QUOTED_SCALAR_STYLE
	}

	return true
}

/*
 * Scan a plain scalar.
 */

func yaml_parser_scan_plain_scalar(parser *yaml_parser_t, token *yaml_token_t) bool {
	var s []byte
	var leading_break []byte
	var trailing_breaks []byte
	var whitespaces []byte
	leading_blanks := false
	indent := parser.indent + 1

	start_mark := parser.mark
	end_mark := parser.mark

	/* Consume the content of the plain scalar. */

	for {
		/* Check for a document indicator. */

		if !cache(parser, 4) {
			return false
		}

		if parser.mark.column == 0 &&
			((parser.buffer[parser.buffer_pos] == '-' &&
				parser.buffer[parser.buffer_pos+1] == '-' &&
				parser.buffer[parser.buffer_pos+2] == '-') ||
				(parser.buffer[parser.buffer_pos] == '.' &&
					parser.buffer[parser.buffer_pos+1] == '.' &&
					parser.buffer[parser.buffer_pos+2] == '.')) &&
			is_blankz_at(parser.buffer, parser.buffer_pos+3) {
			break
		}

		/* Check for a comment. */

		if parser.buffer[parser.buffer_pos] == '#' {
			break
		}

		/* Consume non-blank characters. */

		for !is_blankz_at(parser.buffer, parser.buffer_pos) {
			/* Check for 'x:x' in the flow context. TODO: Fix the test "spec-08-13". */

			if parser.flow_level > 0 &&
				parser.buffer[parser.buffer_pos] == ':' &&
				!is_blankz_at(parser.buffer, parser.buffer_pos+1) {
				yaml_parser_set_scanner_error(parser, "while scanning a plain scalar",
					start_mark, "found unexpected ':'")
				return false
			}

			/* Check for indicators that may end a plain scalar. */
			b := parser.buffer[parser.buffer_pos]
			if (b == ':' && is_blankz_at(parser.buffer, parser.buffer_pos+1)) ||
				(parser.flow_level > 0 &&
					(b == ',' || b == ':' ||
						b == '?' || b == '[' ||
						b == ']' || b == '{' ||
						b == '}')) {
				break
			}

			/* Check if we need to join whitespaces and breaks. */

			if leading_blanks || len(whitespaces) > 0 {
				if leading_blanks {
					/* Do we need to fold line breaks? */

					if leading_break[0] == '\n' {
						if len(trailing_breaks) == 0 {
							s = append(s, ' ')
						} else {
							s = append(s, trailing_breaks...)
							trailing_breaks = trailing_breaks[:0]
						}
						leading_break = leading_break[:0]
					} else {
						s = append(s, leading_break...)
						s = append(s, trailing_breaks...)
						leading_break = leading_break[:0]
						trailing_breaks = trailing_breaks[:0]
					}

					leading_blanks = false
				} else {
					s = append(s, whitespaces...)
					whitespaces = whitespaces[:0]
				}
			}

			/* Copy the character. */

			s = read(parser, s)
			end_mark = parser.mark

			if !cache(parser, 2) {
				return false
			}
		}

		/* Is it the end? */

		if !(is_blank(parser.buffer[parser.buffer_pos]) ||
			is_break_at(parser.buffer, parser.buffer_pos)) {
			break
		}

		/* Consume blank characters. */

		if !cache(parser, 1) {
			return false
		}

		for is_blank(parser.buffer[parser.buffer_pos]) ||
			is_break_at(parser.buffer, parser.buffer_pos) {

			if is_blank(parser.buffer[parser.buffer_pos]) {
				/* Check for tab character that abuse indentation. */

				if leading_blanks && parser.mark.column < indent &&
					is_tab(parser.buffer[parser.buffer_pos]) {
					yaml_parser_set_scanner_error(parser, "while scanning a plain scalar",
						start_mark, "found a tab character that violate indentation")
					return false
				}

				/* Consume a space or a tab character. */

				if !leading_blanks {
					whitespaces = read(parser, whitespaces)
				} else {
					skip(parser)
				}
			} else {
				if !cache(parser, 2) {
					return false
				}

				/* Check if it is a first line break. */

				if !leading_blanks {
					whitespaces = whitespaces[:0]
					leading_break = read_line(parser, leading_break)
					leading_blanks = true
				} else {
					trailing_breaks = read_line(parser, trailing_breaks)
				}
			}
			if !cache(parser, 1) {
				return false
			}
		}

		/* Check indentation level. */

		if parser.flow_level == 0 && parser.mark.column < indent {
			break
		}
	}

	/* Create a token. */

	*token = yaml_token_t{
		token_type: yaml_SCALAR_TOKEN,
		start_mark: start_mark,
		end_mark:   end_mark,
		value:      s,
		style:      yaml_PLAIN_SCALAR_STYLE,
	}

	/* Note that we change the 'simple_key_allowed' flag. */

	if leading_blanks {
		parser.simple_key_allowed = true
	}

	return true
}