It's ages since I've seen LISP for the last time, in any case LISP is (syntacticaly) different enough than anything else (I consider Scheme a dialect of LISP) that people would not expect the same (or even just similar) rules for identifiers in LISP and in a syntacticaly rich langauge with loads of infix operators. As far as ML is considered ... I thought it only allows ' at the start of type variables in things like map:: 'a -> 'b -> ['a] -> ['b], but again it's years since I've seen it for the last time. Besides the singlequote is not as dangrous by far. Especially since it can be used in identifiers in Perl5 as well. Even though it has a special meaning there.