aion-ics/docs/grammar_BNF.md

Aion DSL language for managing ICalendar data

## Grammar in BNF form

```bnf
<program> ::= <statement>* EOF

<statement> ::= <import_stmt>
              | <assignment_stmt>
              | <value_assignment_stmt>
              | <loop_stmt>
              | <export_stmt>
              | <merge_stmt>
              | <filter_stmt>
              | <include_stmt>
              | <conditional_stmt>
              | <structured_event_stmt>
              | <default_declaration>

<import_stmt> ::= "import" <STRING> "as" <IDENTIFIER> ";"

<assignment_stmt> ::= <IDENTIFIER> "=" <declaration> ";"

<value_assignment_stmt> ::= <IDENTIFIER> "=" <value_expr> ";"

<default_declaration> ::= "new" ( <event_decl> | <task_decl> | <pomodoro_decl> ) ";"

<declaration> ::= <event_decl>
                | <task_decl>
                | <pomodoro_decl>

<event_decl> ::= "event" <STRING> <recurrence_expr> <event_time_spec>
               | "event" <STRING> "on" <date> <event_time_spec>

<event_time_spec> ::= "at" <time> "for" <duration>
                    | "from" <time> "to" <time>
                    | "for" <duration> "find" "between" <time> "to" <time>

<recurrence_expr> ::= "daily" ( "at" <time> )?
                    | "weekly" "on" <weekday_list> ( <time_range> | <time_at> )?
                    | "monthly" "on" <NUMBER> ( <time_range> | <time_at> )?
                    | "yearly" "on" <date> ( <time_range> | <time_at> )?

<structured_event_stmt> ::= "event" <IDENTIFIER> "{" <structured_event_field>* "}"

<structured_event_field> ::= "name" ":" <STRING> ","?
                           | "start" ":" <time> ","?
                           | "duration" ":" <duration> ","?
                           | "location" ":" <STRING> ","?
                           | "category" ":" <STRING> ","?

<task_decl> ::= "task" <STRING> "on" <date> <task_time_spec>

<task_time_spec> ::= "at" <time>
                   | "find" "between" <time> "and" <time> ( "using" <strategy> )?

<pomodoro_decl> ::= "pomodoro" <STRING> "on" <date> "at" <time>
                    "repeat" <NUMBER> "times"
                    ( "every" <duration> )?
                    ( "with" <duration> "pause" )?

<loop_stmt> ::= "each" <loop_unit> "from" <loop_start> "to" <loop_end> ( "step" <NUMBER> )? "{" <statement>* "}"

<loop_start> ::= <date>
               | <IDENTIFIER>
               | "today"

<loop_end> ::= <date>
             | <IDENTIFIER>
             | <loop_start> "+" <NUMBER>

<loop_unit> ::= "day" | "days" | "week" | "weeks" | "month" | "months"

<conditional_stmt> ::= "if" "(" <condition> ")" "{" <statement>* "}"
                      ( "else" "if" "(" <condition> ")" "{" <statement>* "}" )*
                      ( "else" "{" <statement>* "}" )?

<filter_stmt> ::= "filter" <IDENTIFIER> "where" <condition> "into" <IDENTIFIER> ";"

<merge_stmt> ::= "merge" <identifier_list> "into" <IDENTIFIER> ";"

<identifier_list> ::= <IDENTIFIER> ( "," <IDENTIFIER> )*

<include_stmt> ::= "include" <IDENTIFIER> "in" <IDENTIFIER> ";"

<export_stmt> ::= "export" <IDENTIFIER> ( "as" <STRING> )? ";"
                | "export" "default" "as" <STRING> ";"
                | "export" "all" ";"

<condition> ::= <IDENTIFIER> <comparison_op> <value>
              | "count" "(" <weekday> ")" "in" "month" <comparison_op> <NUMBER>
              | "category" <comparison_op> <STRING>

<comparison_op> ::= "==" | "!=" | "<" | "<=" | ">" | ">="

<strategy> ::= "random" | "earliest" | "latest"

<value_expr> ::= <date>
               | <time>
               | <duration>
               | <STRING>
               | <NUMBER>
               | <IDENTIFIER>
               | <function_call>
               | <declaration>

<function_call> ::= "count" "(" <weekday> ")" "in" "month"
                  | "weeknumber" "(" <date> ")"

<date> ::= <NUMBER> "." <NUMBER> ( "." <NUMBER> )?

<date_specifier> ::= <date>
                   | <weekday>

<weekday_list> ::= <weekday> ( "," <weekday> )*

<weekday> ::= "Monday" | "Tuesday" | "Wednesday" | "Thursday"
            | "Friday" | "Saturday" | "Sunday"
            | "Mon" | "Tue" | "Wed" | "Thu" | "Fri" | "Sat" | "Sun"

<time> ::= <NUMBER> ":" <NUMBER>

<time_at> ::= "at" <time>

<time_range> ::= "from" <time> "to" <time>

<duration> ::= <NUMBER> <time_unit> ( <NUMBER> <time_unit> )*

<time_unit> ::= "h" | "m"

<value> ::= <STRING>
          | <NUMBER>
          | <IDENTIFIER>

<IDENTIFIER> ::= [a-zA-Z_] [a-zA-Z0-9_]*

<STRING> ::= "\"" ( ~["\\] | "\\" . )* "\""

<NUMBER> ::= [0-9]+

<MONTH_NAME> ::= <JAN> | <FEB> | <MAR> | <APR> | <MAY> | <JUN>
               | <JUL> | <AUG> | <SEP> | <OCT> | <NOV> | <DEC>

<JAN> ::= "jan" | "January"
<FEB> ::= "feb" | "February"
<MAR> ::= "mar" | "March"
<APR> ::= "apr" | "April"
<MAY> ::= "may"
<JUN> ::= "jun" | "June"
<JUL> ::= "jul" | "July"
<AUG> ::= "aug" | "August"
<SEP> ::= "sep" | "September"
<OCT> ::= "oct" | "October"
<NOV> ::= "nov" | "November"
<DEC> ::= "dec" | "December"
```