HOCON grammar

grammar.txt

EOL -> '\n' | '\r' | '\r\n'

Whitespace -> ' ' | '\t'

EscapedSequence -> 
  | '\\' [bfnrt\\] 
  | '\u' [0-9a-fA-F]{4}

QuotedStringElement -> 
  | [^\\"] 
  | EscapedSequence

QuotedString -> 
  | '"' QuotedStringElement* '"'
  | '""'

UnquotedString -> [^$"{}\[\]:=,+#`\^?!@#&\\]+

MultilineString -> '"""' .* '"""'

Numerical -> [0-9]+

Number -> 
  | Numerical
  | Numerical '.' Numerical
  | Numerical '.' [Ee] [+-]? Numerical
  | Numerical '.' Numerical [Ee] [+-]? Numerical

DurationUnit ->
  | 'ns' | 'nanosecond' | 'nanoseconds'
  | 'us' | 'microsecond' | 'microseconds'
  | 'ms' | 'millisecond' | 'milliseconds'
  | 's' | 'second' | 'seconds'
  | 'm' | 'minute' | 'minutes'
  | 'h' | 'hour' | 'hours'
  | 'd' | 'day' | 'days'

Duration -> Number DurationUnit

SizeUnit ->
  | 'B' | 'b' | 'byte' | 'bytes'
  | ‘kB' | 'kilobyte' | 'kilobytes'
  | ‘MB' | 'megabyte' | 'megabytes'
  | ‘GB' | 'gigabyte' | 'gigabytes'
  | ‘TB' | 'terabyte' | 'terabytes'
  | ‘PB' | 'petabyte' | 'petabytes'
  | ‘EB' | 'exabyte' | 'exabytes'
  | ‘ZB' | 'zettabyte' | 'zettabytes'
  | ‘YB' | 'yottabyte' | 'yottabytes'
  | ‘K' | 'k' | 'Ki' | 'KiB' | 'kibibyte' | 'kibibytes'
  | ‘M' | 'm' | 'Mi' | 'MiB' | 'mebibyte' | 'mebibytes'
  | ‘G' | 'g' | 'Gi' | 'GiB' | 'gibibyte' | 'gibibytes'
  | ‘T' | 't' | 'Ti' | 'TiB' | 'tebibyte' | 'tebibytes'
  | ‘P' | 'p' | 'Pi' | 'PiB' | 'pebibyte' | 'pebibytes'
  | ‘E' | 'e' | 'Ei' | 'EiB' | 'exbibyte' | 'exbibytes'
  | ‘Z' | 'z' | 'Zi' | 'ZiB' | 'zebibyte' | 'zebibytes'
  | ‘Y' | 'y' | 'Yi' | 'YiB' | 'yobibyte' | 'yobibytes'

Size -> Number SizeUnit

DeterminedSubstitution -> '${' Key '}'

NonDeterminedSubstitution -> '${?' Key '}'

Substitution ->
  | DeterminedSubstitution
  | NonDeterminedSubstitution

ValueSegment -> 
  | Number
  | Duration
  | Size
  | List
  | Map
  | Substitution
  | UnquotedString
  | QuotedString
  | MultilineString

Value -> ValueSegment ( Whitespace? ValueSegment )*

Separator -> ':' | '='

KeyValuePair -> 
  | Key Whitespace? Separator Whitespace? Value 
  | Key Map

ElementSeparator -> 
  | Whitespace? EOL Whitespace?
  | Whitespace? ',' Whitespace?
  | Whitespace? ',' Whitespace? EOL Whitespace? 

KeyValuePairs ->  
  | KeyValuePair
  | KeyValuePair ElementSeparator
  | KeyValuePair ElementSeparator KeyValuePairs

Map -> '{' WhiteSpace? KeyValuePairs WhiteSpace? '}'

Values ->
  | Value
  | Value ElementSeparator
  | Value ElementSeparator Values

Array -> '[' Whitespace? Values Whitespace? ']'

Document ->
  | Whitespace? EOF
  | Whitespace? KeyValuePairs Whitespace? EOF
  | Whitespace? Map Whitespace? EOF
  | Whitespace? Array Whitespace? EOF

Well then you possibly will be interested to know that DeterminedSubstitution should use domething like '${' Key ('.' Key)? '}'