docs: Missing grammar for functions.

[toqueteos]

Hard to define well but still required.

[toqueteos]

My suggested grammar:
fn_decl: "fn" ident [ generic_decl ] ? "(" args ")" "->" [ arg | "(" args ")" ] block ;
generic_decl: "<" type [ "," type ] + ">" ;
args: arg [ "," arg ] + ;
arg: pat [ ":" type ] ;

I defined my own generic_decl because of #9023.

[huonw]

I think your proposed grammar is incorrect? "->" [arg | "(" args ")"] should probably be "->" type, since it's just the return type of the function.

[toqueteos]

@huonw You are right, my bad.

New proposal:

fn_decl: "fn" ident [ generic_decl ] ? "(" args * ")" "->" type block ;
generic_decl: "<" type [ "," type ] * ">" ;
args: arg [ "," arg ] * ;
arg: pat [ ":" type ] ;

I changed:

• generic_decl from +to *, 1 or more types.
• args so it accepts functions without arguments and 1 argument functions (using * instead of +).

[steveklabnik]

triage: still don't have a grammar here.

[steveklabnik]

We now have a grammar as part of #19278 , so I'm giving this a close.