Declaring Types at Function Declaration

Suggestion for Syntax Sugar:

Would it make sense to permit a simple way to allow a coder to document the function argument type?

f <- function( a:chr, b:data.frame, c:logi ) { ? }

presumably, what comes behind the ?:? should match what ?str? returns.

however, this need not be checked (except perhaps when a particular option is set).  catching errors as soon as possible makes code easier to debug and error messages clearer.

regards,

/iaw