FORMAT.org

A Canonical S-Expression Format

In a 2012 Dr. Dobb’s retrospective, Karl Eiger noted that S-expressions are have been in continuous use longer than any other formats that remain in widespread use today.

Formatting Parameters

dotted_pair

A variety of structures like hash tables can be serialized as basic lists or as a list of dotted-pair cons cells.

Values:

• true
• false

format_nil

Nil is traditionally encoded as the empty list (()), however this can lead to problems in structures which need to serialize fields like Option<Vec<T>>, where both None and Some([]) will serialize to the empty list.

Possible values:

empty_list

()

hash

#nil

nul

nul

*)) Types

Hash Tables

let ht = HashMap::new();
ht.insert("APPLES", 1);
ht.insert("ORANGE", 2);
ht.insert("STRAWBERRIES", 3);

Basic

((APPLES 1) (ORANGES 2) (STRAWBERRIES 3))
((APPLES . 1) (ORANGES . 2) (STRAWBERRIES . 3))

Explicit (distinguishes between data structures)

((variant HashMap) ((APPLES 1) (ORANGES 2) (STRAWBERRIES 3)))

Initializer

(dict ((APPLES 1) 
       (ORANGES 2) 
       (STRAWBERRIES 3)))

Keyword #:REQUIRES keyword

((:APPLES 1 :ORANGES 2 :STRAWBERRIES 3))

Struct

Simple

struct Color {
  r: u8,
  g: u8,
  b: u8,
}

Color { r: 254, g: 1, b: 10 }

Basic

((r 254) (g 1) (b 10))

Explicit

((variant Color) ((r 254) (g 1) (b 10)))

Initializer

(Color :r 254 :g 1 :b 10)

Option

struct Foo {
  x: Option<isize>
}
   
Foo { x: None }
Foo { x: Some(5) }

Basic

The representation of #nil can be configured.

((x 5))
((x #nil))

Explicit

((variant Foo) (x None))
((variant Foo) (x 5))

Simple

(1,2,3)

Basic

(1 2 3)

Explicit

((_field0 1) (_field1 2) (_field2 3))

Vec<u8> or &[u8]

&[41, 41, 19, 1]

Basic

(41 41 19 1)

Lisp

#(41 41 19 1)