Bale

A schema language and binary encoding for serializing data structures.

Specification

Implementations

• Lua
• Pony

Tooling

The baler program can validate schemas and decode/encode data to and from a diagnostic notation.

An example schema

; A 24 bit color value
let color be
  tuple
    r: u8
    g: u8
    b: u8
  end

; Tuples are sequences of multiple data items
tuple
  ; We can have optional items with `maybe`
  position: maybe tuple
    ; `uv`s are compact variable size numbers
    x: uv
    y: uv
  end

  width: u32

  ; A choice of one of multiple data items
  union
    pixels: array color
    image: string
  end
end

Some examples of encodings

Schema	Value	Encoded
void
bool	false	00
bool	true	01
maybe u16	just 12	01 00 0c
maybe i8	nothing	00
2 u8	3, 4	03 04
uv	2200	f8 a8

What does bale not do

• Versioning of schemas
• Random access
• Self description of data

Differences from XDR

• No four byte alignment
• Use of variable size integers instead of a fixed 32 bits for length encoding.
• Let bindings can have parameters unlike XDR typedefs
• Fewer predefined types

Code generation

Code generation is not required and encoding/decoding bale is trivial, this means you are not limited to a subset of languages.

But generating code is still possible if you really want to.