-------------------------------------------------------------------------------
--             the Berry's bytecode file structure (version 1)
--
--                             description
--
--         a double dash ('--') start a line comment.
-- a: n    means that the size of entity 'a' is 'n' bytes.
-- 'a: .n  means that the size of entity 'a' is 'n' bits.
-- a:
--      b  means that the entity 'a' is realized by the 'b' structure.
-- a:
--      b
--      c  'b' and 'c' are arranged in a compact order (one byte alignment).
-- [a]     means that structure 'a' can be repeated 0 to any times.
-- [a](b)  means that structure 'a' can be repeated 'b' times.
-- a | b   means that the entity can be implemented by structure 'a' or 'b'.
-- a -> b  is equivalent to 'a:
--                               b'.
--         only the first entity is a file entity (the root).
-------------------------------------------------------------------------------

bytecode_file:  -- little endian
    header
    global_desc
    main_function

header: 8
    magic_number: 3 -- 0xbecdfe (berry code file)
    version: 1      -- update with file structure definition
    integer_size: .1
    float_size: .1
    -- reserved space

main_function -> function

global_desc:
    builtin_count: 4
    global_count: 4
    global_name -> [
            string
        ](global_count)

function:
    information:
        function_name:
            string
        source:
            string
        argc: 1   -- arguments count
        nstack: 1 -- number of stack size by this function
        extra: 2  -- extra data
    bytecode:
        code_size: 4
        code_array -> [ -- bytecode array
                instruction: 4
            ](code_size)
    constant_table:
        constant_count: 4
        [constant_value](constant_count)
    proto_table:
        proto_count: 4
        [function](proto_count)
    upval_table:
        upval_count: 1
        upvals -> [
                instack: 1
                index: 1
            ](upval_count)
    debug_info:
        -- reserved

constant_value:
    type: 1  -- type of value
    integer | float | string | class

string:
    string_size: 2
    byte_array: string_size

class:
    class_name:
        string
    member_count: 4   -- number of member variables
    method_count: 4   -- number of method
    method_table -> [
            string    -- method name
            function  -- method function body
        ](method_count)
    member_index_table -> [
            string    -- member name
        ](member_count)

nil: 1
boolean: 1
integer: 4 or 8
float: 4 or 8