yaml.pgx

# This is the Pegex grammar for YAML 1.2.

# It is currently in a fledgling state. It is only intended to pass the YAML
# TestML Suite. Eventually it will be able to parse any valid YAML 1.2
# document.

# To Do:
# - Comments (maybe as whitespace)
# - Directives
# - Tags

%grammar yaml
%version 1.2

yaml_stream: yaml_document*

yaml_document:
    document_header?
    (
        flow_collection |
        block_node |
        block_scalar
    )
    document_footer?

document_header:
    / ( <DASH><DASH><DASH> ) <ws> /

document_footer:
    / <DOT><DOT><DOT> <EOL> /

block_node:
    block_seq |
    block_map |
    block_scalar

block_map:
    indent
    block_pair+
    undent

block_seq:
    indent
    block_elem+
    undent

block_scalar:
    double_quoted |
    single_quoted |
    plain_string |
    empty_string

#     literal_string |
#     folded_string |

block_pair:
    indentation block_key /~<COLON>~/ block_value BREAK

block_elem:
    indentation /<DASH><SPACE>/ block_value BREAK

block_key:
    double_quoted |
    single_quoted |
    plain_string

block_value:
    flow_collection |
    block_node

flow_collection:
    flow_map |
    flow_seq

flow_node:
    flow_collection |
    flow_scalar

flow_map:
    / ~ <LCURLY> ~ /
        flow_pair* % / ~ <COMMA> ~ /
    / ~ <RCURLY> ~ /

flow_seq:
    / ~ <LSQUARE> ~ /
        flow_node* % / ~ <COMMA> ~ /
    / ~ <RSQUARE> ~ /

flow_scalar:
    double_quoted |
    single_quoted |
    plain_string

flow_pair:
    flow_node / ~ <COLON> ~ / flow_node

double_quoted: /
    <DOUBLE>
        ((:
            <BACK><BACK> |
            <BACK><DOUBLE> |
            [^<DOUBLE><BREAK>]
        )*)
    <DOUBLE>
/

single_quoted: /
    <SINGLE>
        ((:
            <SINGLE><SINGLE> |
            [^<SINGLE>]
        )*)
    <SINGLE>
/

plain_string: / ( [^<non_starters>] [^<non_plain>]* ) /

empty_string: //

literal_string: `literal_string not yet supported`

folded_string: `folded_string not yet supported`

non_starters: /
    <PERCENT>
    <SINGLE>
    <DOUBLE>
    <SPACE>
/

non_plain: /
    <COLON>
    <BREAK>
/