8.19 Extension-only syntax

Some syntactic constructions are accepted during parsing and rejected during type checking. These syntactic constructions can therefore not be used directly in vanilla OCaml. However, -ppx rewriters and other external tools can exploit this parser leniency to extend the language with these new syntactic constructions by rewriting them to vanilla constructions.

8.19.1 Extension operators

infix-symbol	::=	...
	∣	# {operator-chars} # {operator-char \| #}

Operator names starting with a # character and containing more than one # character are reserved for extensions.

8.19.2 Extension literals

float-literal	::=	...
	∣	[-] (0…9) { 0…9∣ _ } [. { 0…9∣ _ }] [(e∣ E) [+∣ -] (0…9) { 0…9∣ _ }] [g…z∣ G…Z]
	∣	[-] (0x∣ 0X) (0…9∣ A…F∣ a…f) { 0…9∣ A…F∣ a…f∣ _ } [. { 0…9∣ A…F∣ a…f∣ _ }] [(p∣ P) [+∣ -] (0…9) { 0…9∣ _ }] [g…z∣ G…Z]

int-literal	::=	...
	∣	[-] (0…9) { 0…9 ∣ _ }[g…z∣ G…Z]
	∣	[-] (0x∣ 0X) (0…9∣ A…F∣ a…f) { 0…9∣ A…F∣ a…f∣ _ } [g…z∣ G…Z]
	∣	[-] (0o∣ 0O) (0…7) { 0…7∣ _ } [g…z∣ G…Z]
	∣	[-] (0b∣ 0B) (0…1) { 0…1∣ _ } [g…z∣ G…Z]

Int and float literals followed by an one-letter identifier in the range [g..z∣ G..Z] are extension-only literals.