On Wed, Jul 7, 2010 at 12:23 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote: > Should an expression be required at the end? A `module', `unit', or > `class' body can consist of just definitions. Similarly, if an > internal-definition context ends with a definition, we could define the > result to be `(void)', which is what the `block' form does. > > I think it's better to require an expression at the end, partly on the > grounds that the internal-definition block is supposed to return a > value (unlike the body of `module', etc.) and partly to avoid making > forms like > > (define (f x) > x > (define (g y) > y)) > > legal when they are almost certainly mistakes.
Macros constructing sequences of def-or-expr for implicit begin (as found in let, lambda, parameterize, etc.) won't always know if the sequence is empty or non-empty, and whether it is terminated by an expression or definition. If a begin-like sequence ends with a definition, currently a macro must add an expression such as (void) to follow it. If it ends with an expression, the macro must *not* add such an expression, because that changes the return value. It would be far more convenient if primitive forms worked with any sequence of def-or-expr so that each wrapper macro did not have to implement its own local-expand loop to figure out how the sequence ends, and as always it is much nicer to write macros when sequences can be zero-length. --Carl _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
