func yaml_parser_parse_block_mapping_key(parser *yaml_parser_t, event *yaml_event_t, first bool) bool {
	if first {
		token := peek_token(parser)
		parser.marks = append(parser.marks, token.start_mark)
		skip_token(parser)
	}
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if len(parser.tail_comment) > 0 {
		*event = yaml_event_t{
			typ:          yaml_TAIL_COMMENT_EVENT,
			start_mark:   token.start_mark,
			end_mark:     token.end_mark,
			foot_comment: parser.tail_comment,
		}
		parser.tail_comment = nil
		return true
	}
	if token.typ == yaml_KEY_TOKEN {
		mark := token.end_mark
		skip_token(parser)
		token = peek_token(parser)
		if token == nil {
			return false
		}
		if token.typ != yaml_KEY_TOKEN &&
			token.typ != yaml_VALUE_TOKEN &&
			token.typ != yaml_BLOCK_END_TOKEN {
			parser.states = append(parser.states, yaml_PARSE_BLOCK_MAPPING_VALUE_STATE)
			return yaml_parser_parse_node(parser, event, true, true)
		} else {
			parser.state = yaml_PARSE_BLOCK_MAPPING_VALUE_STATE
			return yaml_parser_process_empty_scalar(parser, event, mark)
		}
	} else if token.typ == yaml_BLOCK_END_TOKEN {
		parser.state = parser.states[len(parser.states)-1]
		parser.states = parser.states[:len(parser.states)-1]
		parser.marks = parser.marks[:len(parser.marks)-1]
		*event = yaml_event_t{
			typ:        yaml_MAPPING_END_EVENT,
			start_mark: token.start_mark,
			end_mark:   token.end_mark,
		}
		yaml_parser_set_event_comments(parser, event)
		skip_token(parser)
		return true
	}
	context_mark := parser.marks[len(parser.marks)-1]
	parser.marks = parser.marks[:len(parser.marks)-1]
	return yaml_parser_set_parser_error_context(parser,
		"while parsing a block mapping", context_mark,
		"did not find expected key", token.start_mark)
}
Parse the productions:
block_mapping        ::= BLOCK-MAPPING_START
*******************
((KEY block_node_or_indentless_sequence?)?
*** *
(VALUE block_node_or_indentless_sequence?)?)*

BLOCK-END
*********
package yaml
import (
	"bytes"
)
func peek_token(parser *yaml_parser_t) *yaml_token_t {
	if parser.token_available || yaml_parser_fetch_more_tokens(parser) {
		token := &parser.tokens[parser.tokens_head]
		yaml_parser_unfold_comments(parser, token)
		return token
	}
	return nil
}
func yaml_parser_unfold_comments(parser *yaml_parser_t, token *yaml_token_t) {
	for parser.comments_head < len(parser.comments) && token.start_mark.index >= parser.comments[parser.comments_head].token_mark.index {
		comment := &parser.comments[parser.comments_head]
		if len(comment.head) > 0 {
			if token.typ == yaml_BLOCK_END_TOKEN {
				break
			}
			if len(parser.head_comment) > 0 {
				parser.head_comment = append(parser.head_comment, '\n')
			}
			parser.head_comment = append(parser.head_comment, comment.head...)
		}
		if len(comment.foot) > 0 {
			if len(parser.foot_comment) > 0 {
				parser.foot_comment = append(parser.foot_comment, '\n')
			}
			parser.foot_comment = append(parser.foot_comment, comment.foot...)
		}
		if len(comment.line) > 0 {
			if len(parser.line_comment) > 0 {
				parser.line_comment = append(parser.line_comment, '\n')
			}
			parser.line_comment = append(parser.line_comment, comment.line...)
		}
		*comment = yaml_comment_t{}
		parser.comments_head++
	}
}
func skip_token(parser *yaml_parser_t) {
	parser.token_available = false
	parser.tokens_parsed++
	parser.stream_end_produced = parser.tokens[parser.tokens_head].typ == yaml_STREAM_END_TOKEN
	parser.tokens_head++
}
func yaml_parser_parse(parser *yaml_parser_t, event *yaml_event_t) bool {
	*event = yaml_event_t{}
	if parser.stream_end_produced || parser.error != yaml_NO_ERROR || parser.state == yaml_PARSE_END_STATE {
		return true
	}
	return yaml_parser_state_machine(parser, event)
}
func yaml_parser_set_parser_error(parser *yaml_parser_t, problem string, problem_mark yaml_mark_t) bool {
	parser.error = yaml_PARSER_ERROR
	parser.problem = problem
	parser.problem_mark = problem_mark
	return false
}
func yaml_parser_set_parser_error_context(parser *yaml_parser_t, context string, context_mark yaml_mark_t, problem string, problem_mark yaml_mark_t) bool {
	parser.error = yaml_PARSER_ERROR
	parser.context = context
	parser.context_mark = context_mark
	parser.problem = problem
	parser.problem_mark = problem_mark
	return false
}
func yaml_parser_state_machine(parser *yaml_parser_t, event *yaml_event_t) bool {
	switch parser.state {
	case yaml_PARSE_STREAM_START_STATE:
		return yaml_parser_parse_stream_start(parser, event)
	case yaml_PARSE_IMPLICIT_DOCUMENT_START_STATE:
		return yaml_parser_parse_document_start(parser, event, true)
	case yaml_PARSE_DOCUMENT_START_STATE:
		return yaml_parser_parse_document_start(parser, event, false)
	case yaml_PARSE_DOCUMENT_CONTENT_STATE:
		return yaml_parser_parse_document_content(parser, event)
	case yaml_PARSE_DOCUMENT_END_STATE:
		return yaml_parser_parse_document_end(parser, event)
	case yaml_PARSE_BLOCK_NODE_STATE:
		return yaml_parser_parse_node(parser, event, true, false)
	case yaml_PARSE_BLOCK_NODE_OR_INDENTLESS_SEQUENCE_STATE:
		return yaml_parser_parse_node(parser, event, true, true)
	case yaml_PARSE_FLOW_NODE_STATE:
		return yaml_parser_parse_node(parser, event, false, false)
	case yaml_PARSE_BLOCK_SEQUENCE_FIRST_ENTRY_STATE:
		return yaml_parser_parse_block_sequence_entry(parser, event, true)
	case yaml_PARSE_BLOCK_SEQUENCE_ENTRY_STATE:
		return yaml_parser_parse_block_sequence_entry(parser, event, false)
	case yaml_PARSE_INDENTLESS_SEQUENCE_ENTRY_STATE:
		return yaml_parser_parse_indentless_sequence_entry(parser, event)
	case yaml_PARSE_BLOCK_MAPPING_FIRST_KEY_STATE:
		return yaml_parser_parse_block_mapping_key(parser, event, true)
	case yaml_PARSE_BLOCK_MAPPING_KEY_STATE:
		return yaml_parser_parse_block_mapping_key(parser, event, false)
	case yaml_PARSE_BLOCK_MAPPING_VALUE_STATE:
		return yaml_parser_parse_block_mapping_value(parser, event)
	case yaml_PARSE_FLOW_SEQUENCE_FIRST_ENTRY_STATE:
		return yaml_parser_parse_flow_sequence_entry(parser, event, true)
	case yaml_PARSE_FLOW_SEQUENCE_ENTRY_STATE:
		return yaml_parser_parse_flow_sequence_entry(parser, event, false)
	case yaml_PARSE_FLOW_SEQUENCE_ENTRY_MAPPING_KEY_STATE:
		return yaml_parser_parse_flow_sequence_entry_mapping_key(parser, event)
	case yaml_PARSE_FLOW_SEQUENCE_ENTRY_MAPPING_VALUE_STATE:
		return yaml_parser_parse_flow_sequence_entry_mapping_value(parser, event)
	case yaml_PARSE_FLOW_SEQUENCE_ENTRY_MAPPING_END_STATE:
		return yaml_parser_parse_flow_sequence_entry_mapping_end(parser, event)
	case yaml_PARSE_FLOW_MAPPING_FIRST_KEY_STATE:
		return yaml_parser_parse_flow_mapping_key(parser, event, true)
	case yaml_PARSE_FLOW_MAPPING_KEY_STATE:
		return yaml_parser_parse_flow_mapping_key(parser, event, false)
	case yaml_PARSE_FLOW_MAPPING_VALUE_STATE:
		return yaml_parser_parse_flow_mapping_value(parser, event, false)
	case yaml_PARSE_FLOW_MAPPING_EMPTY_VALUE_STATE:
		return yaml_parser_parse_flow_mapping_value(parser, event, true)
	default:
		panic("invalid parser state")
	}
}
func yaml_parser_parse_stream_start(parser *yaml_parser_t, event *yaml_event_t) bool {
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if token.typ != yaml_STREAM_START_TOKEN {
		return yaml_parser_set_parser_error(parser, "did not find expected <stream-start>", token.start_mark)
	}
	parser.state = yaml_PARSE_IMPLICIT_DOCUMENT_START_STATE
	*event = yaml_event_t{
		typ:        yaml_STREAM_START_EVENT,
		start_mark: token.start_mark,
		end_mark:   token.end_mark,
		encoding:   token.encoding,
	}
	skip_token(parser)
	return true
}
func yaml_parser_parse_document_start(parser *yaml_parser_t, event *yaml_event_t, implicit bool) bool {
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if !implicit {
		for token.typ == yaml_DOCUMENT_END_TOKEN {
			skip_token(parser)
			token = peek_token(parser)
			if token == nil {
				return false
			}
		}
	}
	if implicit && token.typ != yaml_VERSION_DIRECTIVE_TOKEN &&
		token.typ != yaml_TAG_DIRECTIVE_TOKEN &&
		token.typ != yaml_DOCUMENT_START_TOKEN &&
		token.typ != yaml_STREAM_END_TOKEN {
		if !yaml_parser_process_directives(parser, nil, nil) {
			return false
		}
		parser.states = append(parser.states, yaml_PARSE_DOCUMENT_END_STATE)
		parser.state = yaml_PARSE_BLOCK_NODE_STATE
		var head_comment []byte
		if len(parser.head_comment) > 0 {
			for i := len(parser.head_comment) - 1; i > 0; i-- {
				if parser.head_comment[i] == '\n' {
					if i == len(parser.head_comment)-1 {
						head_comment = parser.head_comment[:i]
						parser.head_comment = parser.head_comment[i+1:]
						break
					} else if parser.head_comment[i-1] == '\n' {
						head_comment = parser.head_comment[:i-1]
						parser.head_comment = parser.head_comment[i+1:]
						break
					}
				}
			}
		}
		*event = yaml_event_t{
			typ:        yaml_DOCUMENT_START_EVENT,
			start_mark: token.start_mark,
			end_mark:   token.end_mark,
			head_comment: head_comment,
		}
	} else if token.typ != yaml_STREAM_END_TOKEN {
		var version_directive *yaml_version_directive_t
		var tag_directives []yaml_tag_directive_t
		start_mark := token.start_mark
		if !yaml_parser_process_directives(parser, &version_directive, &tag_directives) {
			return false
		}
		token = peek_token(parser)
		if token == nil {
			return false
		}
		if token.typ != yaml_DOCUMENT_START_TOKEN {
			yaml_parser_set_parser_error(parser,
				"did not find expected <document start>", token.start_mark)
			return false
		}
		parser.states = append(parser.states, yaml_PARSE_DOCUMENT_END_STATE)
		parser.state = yaml_PARSE_DOCUMENT_CONTENT_STATE
		end_mark := token.end_mark
		*event = yaml_event_t{
			typ:               yaml_DOCUMENT_START_EVENT,
			start_mark:        start_mark,
			end_mark:          end_mark,
			version_directive: version_directive,
			tag_directives:    tag_directives,
			implicit:          false,
		}
		skip_token(parser)
	} else {
		parser.state = yaml_PARSE_END_STATE
		*event = yaml_event_t{
			typ:        yaml_STREAM_END_EVENT,
			start_mark: token.start_mark,
			end_mark:   token.end_mark,
		}
		skip_token(parser)
	}
	return true
}
func yaml_parser_parse_document_content(parser *yaml_parser_t, event *yaml_event_t) bool {
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if token.typ == yaml_VERSION_DIRECTIVE_TOKEN ||
		token.typ == yaml_TAG_DIRECTIVE_TOKEN ||
		token.typ == yaml_DOCUMENT_START_TOKEN ||
		token.typ == yaml_DOCUMENT_END_TOKEN ||
		token.typ == yaml_STREAM_END_TOKEN {
		parser.state = parser.states[len(parser.states)-1]
		parser.states = parser.states[:len(parser.states)-1]
		return yaml_parser_process_empty_scalar(parser, event,
			token.start_mark)
	}
	return yaml_parser_parse_node(parser, event, true, false)
}
func yaml_parser_parse_document_end(parser *yaml_parser_t, event *yaml_event_t) bool {
	token := peek_token(parser)
	if token == nil {
		return false
	}
	start_mark := token.start_mark
	end_mark := token.start_mark
	implicit := true
	if token.typ == yaml_DOCUMENT_END_TOKEN {
		end_mark = token.end_mark
		skip_token(parser)
		implicit = false
	}
	parser.tag_directives = parser.tag_directives[:0]
	parser.state = yaml_PARSE_DOCUMENT_START_STATE
	*event = yaml_event_t{
		typ:        yaml_DOCUMENT_END_EVENT,
		start_mark: start_mark,
		end_mark:   end_mark,
		implicit:   implicit,
	}
	yaml_parser_set_event_comments(parser, event)
	if len(event.head_comment) > 0 && len(event.foot_comment) == 0 {
		event.foot_comment = event.head_comment
		event.head_comment = nil
	}
	return true
}
func yaml_parser_set_event_comments(parser *yaml_parser_t, event *yaml_event_t) {
	event.head_comment = parser.head_comment
	event.line_comment = parser.line_comment
	event.foot_comment = parser.foot_comment
	parser.head_comment = nil
	parser.line_comment = nil
	parser.foot_comment = nil
	parser.tail_comment = nil
	parser.stem_comment = nil
}
func yaml_parser_parse_node(parser *yaml_parser_t, event *yaml_event_t, block, indentless_sequence bool) bool {
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if token.typ == yaml_ALIAS_TOKEN {
		parser.state = parser.states[len(parser.states)-1]
		parser.states = parser.states[:len(parser.states)-1]
		*event = yaml_event_t{
			typ:        yaml_ALIAS_EVENT,
			start_mark: token.start_mark,
			end_mark:   token.end_mark,
			anchor:     token.value,
		}
		yaml_parser_set_event_comments(parser, event)
		skip_token(parser)
		return true
	}
	start_mark := token.start_mark
	end_mark := token.start_mark
	var tag_token bool
	var tag_handle, tag_suffix, anchor []byte
	var tag_mark yaml_mark_t
	if token.typ == yaml_ANCHOR_TOKEN {
		anchor = token.value
		start_mark = token.start_mark
		end_mark = token.end_mark
		skip_token(parser)
		token = peek_token(parser)
		if token == nil {
			return false
		}
		if token.typ == yaml_TAG_TOKEN {
			tag_token = true
			tag_handle = token.value
			tag_suffix = token.suffix
			tag_mark = token.start_mark
			end_mark = token.end_mark
			skip_token(parser)
			token = peek_token(parser)
			if token == nil {
				return false
			}
		}
	} else if token.typ == yaml_TAG_TOKEN {
		tag_token = true
		tag_handle = token.value
		tag_suffix = token.suffix
		start_mark = token.start_mark
		tag_mark = token.start_mark
		end_mark = token.end_mark
		skip_token(parser)
		token = peek_token(parser)
		if token == nil {
			return false
		}
		if token.typ == yaml_ANCHOR_TOKEN {
			anchor = token.value
			end_mark = token.end_mark
			skip_token(parser)
			token = peek_token(parser)
			if token == nil {
				return false
			}
		}
	}
	var tag []byte
	if tag_token {
		if len(tag_handle) == 0 {
			tag = tag_suffix
			tag_suffix = nil
		} else {
			for i := range parser.tag_directives {
				if bytes.Equal(parser.tag_directives[i].handle, tag_handle) {
					tag = append([]byte(nil), parser.tag_directives[i].prefix...)
					tag = append(tag, tag_suffix...)
					break
				}
			}
			if len(tag) == 0 {
				yaml_parser_set_parser_error_context(parser,
					"while parsing a node", start_mark,
					"found undefined tag handle", tag_mark)
				return false
			}
		}
	}
	implicit := len(tag) == 0
	if indentless_sequence && token.typ == yaml_BLOCK_ENTRY_TOKEN {
		end_mark = token.end_mark
		parser.state = yaml_PARSE_INDENTLESS_SEQUENCE_ENTRY_STATE
		*event = yaml_event_t{
			typ:        yaml_SEQUENCE_START_EVENT,
			start_mark: start_mark,
			end_mark:   end_mark,
			anchor:     anchor,
			tag:        tag,
			implicit:   implicit,
			style:      yaml_style_t(yaml_BLOCK_SEQUENCE_STYLE),
		}
		return true
	}
	if token.typ == yaml_SCALAR_TOKEN {
		var plain_implicit, quoted_implicit bool
		end_mark = token.end_mark
		if (len(tag) == 0 && token.style == yaml_PLAIN_SCALAR_STYLE) || (len(tag) == 1 && tag[0] == '!') {
			plain_implicit = true
		} else if len(tag) == 0 {
			quoted_implicit = true
		}
		parser.state = parser.states[len(parser.states)-1]
		parser.states = parser.states[:len(parser.states)-1]
		*event = yaml_event_t{
			typ:             yaml_SCALAR_EVENT,
			start_mark:      start_mark,
			end_mark:        end_mark,
			anchor:          anchor,
			tag:             tag,
			value:           token.value,
			implicit:        plain_implicit,
			quoted_implicit: quoted_implicit,
			style:           yaml_style_t(token.style),
		}
		yaml_parser_set_event_comments(parser, event)
		skip_token(parser)
		return true
	}
	if token.typ == yaml_FLOW_SEQUENCE_START_TOKEN {
		end_mark = token.end_mark
		parser.state = yaml_PARSE_FLOW_SEQUENCE_FIRST_ENTRY_STATE
		*event = yaml_event_t{
			typ:        yaml_SEQUENCE_START_EVENT,
			start_mark: start_mark,
			end_mark:   end_mark,
			anchor:     anchor,
			tag:        tag,
			implicit:   implicit,
			style:      yaml_style_t(yaml_FLOW_SEQUENCE_STYLE),
		}
		yaml_parser_set_event_comments(parser, event)
		return true
	}
	if token.typ == yaml_FLOW_MAPPING_START_TOKEN {
		end_mark = token.end_mark
		parser.state = yaml_PARSE_FLOW_MAPPING_FIRST_KEY_STATE
		*event = yaml_event_t{
			typ:        yaml_MAPPING_START_EVENT,
			start_mark: start_mark,
			end_mark:   end_mark,
			anchor:     anchor,
			tag:        tag,
			implicit:   implicit,
			style:      yaml_style_t(yaml_FLOW_MAPPING_STYLE),
		}
		yaml_parser_set_event_comments(parser, event)
		return true
	}
	if block && token.typ == yaml_BLOCK_SEQUENCE_START_TOKEN {
		end_mark = token.end_mark
		parser.state = yaml_PARSE_BLOCK_SEQUENCE_FIRST_ENTRY_STATE
		*event = yaml_event_t{
			typ:        yaml_SEQUENCE_START_EVENT,
			start_mark: start_mark,
			end_mark:   end_mark,
			anchor:     anchor,
			tag:        tag,
			implicit:   implicit,
			style:      yaml_style_t(yaml_BLOCK_SEQUENCE_STYLE),
		}
		if parser.stem_comment != nil {
			event.head_comment = parser.stem_comment
			parser.stem_comment = nil
		}
		return true
	}
	if block && token.typ == yaml_BLOCK_MAPPING_START_TOKEN {
		end_mark = token.end_mark
		parser.state = yaml_PARSE_BLOCK_MAPPING_FIRST_KEY_STATE
		*event = yaml_event_t{
			typ:        yaml_MAPPING_START_EVENT,
			start_mark: start_mark,
			end_mark:   end_mark,
			anchor:     anchor,
			tag:        tag,
			implicit:   implicit,
			style:      yaml_style_t(yaml_BLOCK_MAPPING_STYLE),
		}
		return true
	}
	if len(anchor) > 0 || len(tag) > 0 {
		parser.state = parser.states[len(parser.states)-1]
		parser.states = parser.states[:len(parser.states)-1]
		*event = yaml_event_t{
			typ:             yaml_SCALAR_EVENT,
			start_mark:      start_mark,
			end_mark:        end_mark,
			anchor:          anchor,
			tag:             tag,
			implicit:        implicit,
			quoted_implicit: false,
			style:           yaml_style_t(yaml_PLAIN_SCALAR_STYLE),
		}
		return true
	}
	context := "while parsing a flow node"
	if block {
		context = "while parsing a block node"
	}
	yaml_parser_set_parser_error_context(parser, context, start_mark,
		"did not find expected node content", token.start_mark)
	return false
}
func yaml_parser_parse_block_sequence_entry(parser *yaml_parser_t, event *yaml_event_t, first bool) bool {
	if first {
		token := peek_token(parser)
		parser.marks = append(parser.marks, token.start_mark)
		skip_token(parser)
	}
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if token.typ == yaml_BLOCK_ENTRY_TOKEN {
		mark := token.end_mark
		prior_head := len(parser.head_comment)
		skip_token(parser)
		token = peek_token(parser)
		if token == nil {
			return false
		}
		if prior_head > 0 && token.typ == yaml_BLOCK_SEQUENCE_START_TOKEN {
			parser.stem_comment = parser.head_comment[:prior_head]
			if len(parser.head_comment) == prior_head {
				parser.head_comment = nil
			} else {
				parser.head_comment = append([]byte(nil), parser.head_comment[prior_head+1:]...)
			}
		}
		if token.typ != yaml_BLOCK_ENTRY_TOKEN && token.typ != yaml_BLOCK_END_TOKEN {
			parser.states = append(parser.states, yaml_PARSE_BLOCK_SEQUENCE_ENTRY_STATE)
			return yaml_parser_parse_node(parser, event, true, false)
		} else {
			parser.state = yaml_PARSE_BLOCK_SEQUENCE_ENTRY_STATE
			return yaml_parser_process_empty_scalar(parser, event, mark)
		}
	}
	if token.typ == yaml_BLOCK_END_TOKEN {
		parser.state = parser.states[len(parser.states)-1]
		parser.states = parser.states[:len(parser.states)-1]
		parser.marks = parser.marks[:len(parser.marks)-1]
		*event = yaml_event_t{
			typ:        yaml_SEQUENCE_END_EVENT,
			start_mark: token.start_mark,
			end_mark:   token.end_mark,
		}
		skip_token(parser)
		return true
	}
	context_mark := parser.marks[len(parser.marks)-1]
	parser.marks = parser.marks[:len(parser.marks)-1]
	return yaml_parser_set_parser_error_context(parser,
		"while parsing a block collection", context_mark,
		"did not find expected '-' indicator", token.start_mark)
}
func yaml_parser_parse_indentless_sequence_entry(parser *yaml_parser_t, event *yaml_event_t) bool {
	token := peek_token(parser)
	if token == nil {
		return false
	}
	if token.typ == yaml_BLOCK_ENTRY_TOKEN {
		mark := token.end_mark
		skip_token(parser)
		token = peek_token(parser)
		if token == nil {
			return false
		}
		if token.typ != yaml_BLOCK_ENTRY_TOKEN &&
			token.typ != yaml_KEY_TOKEN &&
			token.typ != yaml_VALUE_TOKEN &&
			token.typ != yaml_BLOCK_END_TOKEN {
			parser.states = append(parser.states, yaml_PARSE_INDENTLESS_SEQUENCE_ENTRY_STATE)
			return yaml_parser_parse_node(parser, event, true, false)
		}
		parser.state = yaml_PARSE_INDENTLESS_SEQUENCE_ENTRY_STATE
		return yaml_parser_process_empty_scalar(parser, event, mark)
	}
	parser.state = parser.states[len(parser.states)-1]
	parser.states = parser.states[:len(parser.states)-1]
	*event = yaml_event_t{
		typ:        yaml_SEQUENCE_END_EVENT,
		start_mark: token.start_mark,
		end_mark:   token.start_mark,  
	}
	return true
}