~$ perl6
> grammar Cols { rule TOP { (\s?<coln>)+ }; rule coln { (\S+) } }
(Cols)
> grammar Cols2 { rule TOP { (\s?<coln>)+ } rule coln { (\S+) } }
===SORRY!===
Two terms in a row
at <unknown file>:1
------> ammar Cols2 { rule TOP { (\s?<coln>)+ } ⏏rule coln { (\S+) } }
    expecting any of:
        statement list
        prefix or term
        prefix or meta-prefix
        new name to be defined
        infix stopper
        horizontal whitespace
        postfix
        infix or meta-infix
        statement end
        statement modifier
        statement modifier loop
> grammar Cols2 { rule TOP { (\s?<coln>)+ } rule coln { (\S+) } }
Null PMC access in get_string()
> grammar Cols2 { rule TOP { (\s?<coln>)+ } rule coln { (\S+) } }
Null PMC access in get_string()