# s-expressions

s-expressions are the good idea hiding in Lisp. Use them in place of JSON or
Protobuf for program-to-program communication.

Advantages:

- Very simple and easy to parse
- Plaintext
- Compresses well

s-expressions are relatively easy for a human to read and write, but you should
be *inspecting* it more often than writing it by hand.

A <300 line C implementation is provided further down. It's used like so:

```c
char *dept = "finance";
int salary = 90000;
char *name = "Jane Doe";
ha_sexp_printf("(ads)", dept, salary, name);
// prints (finance 90000 "Jane Doe")
```

To scan this back in:

```c
char dept[16];
int salary;
char *name = NULL;
int n = ha_sexp_scanf("(ads)", &dept, sizeof(dept), &salary, &name);
if (n != 5) {
	// Input does not match spec
}
// ...
free(value);
```

Grammar (McKeeman form):

	sexpr
		value
		'(' sexpr ')'

	value
		atom
		string
		integer
		float

	atom
		alnum
		atom alnum

	string
		'""'
		'"' characters '"'

	characters
		character
		character characters

	character
		'0020' . '10FFFF' - '"' - '\'
		"\u" hex hex hex hex
		'\' '\'
		'\' '"'

	digit
		'0' . '9'

	digits
		digit
		digit digits

	integer
		digits

	float
		digits '.' digits

	alnum
		digit
		'a' . 'z'
		'_'
		'-'

	hex
		'a' . 'f'
		digit

Put that on your business card, Crockford.