item = const_item
| fn_item
| static_item
const_item = `const` ident = const_expression
ident = ?
const_expression = ?
fn_item = `fn` ident ( ) { [statement, 0 or more] }
statement = reg_statement
| mem_statement
| if_statement
| loop_statement
reg_statement = ?
mem_statement = ?
if_statement = ?
loop_statement = ?
static_item = `static` ident : type_signature = static_expression
type_signature = ?
static_expression = ?