STD.pm approximation

STD.pm:

proto rule statement_control   { <...> }
rule statement_control:if      { ... }
rule statement_control:while   { ... }
rule statement_control:for     { ... }
...

Rakudo:

rule statement_control {
    | <if_statement>
    | <while_statement>
    | <for_statement>
    | ...
}
rule if_statement { ... }