On Fri, Jun 7, 2013 at 1:42 AM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
> At Thu, 9 May 2013 16:22:54 +0200, Laurent wrote: > > I've always wondered why the syntax of keywords implied two elements: the > > #:keyword and the identifier. > > I find that quite heavy for procedure headers, and most of the time I use > > the same symbol for the identifier and the keyword (and when I don't it's > > because I'm simply lazy and use a shorter identifier). > > > > Is there a rationale somewhere for that? > > The rationale is to make function definitions have the same shape as > function calls. > I see what you mean, though I wouldn't make a strong case of it (maybe I'm missing something). >From time to time, I really feel frustrated by the current function header style. What I'd really like, for the sake of flexibility / ease of use, is to have no explicit keyword argument, but all arguments are implicit ones, so that you can call a function by mixing by position and by name as you like, without having specified so in the function's header. (Visual Basic[1] and Python[2] do something along these lines.) For example: (define (foo x y [z 3] [t 4]) ....) (foo 1 2 5) (foo #:z 5 #:y 1 #:x 2) (foo 1 #:t 6 #:y 3) (foo #:x 3) Error: missing mandatory argument `y' (apply/kw f 2 #:y 3 '(5) '((t . 3))) In particular, one would then not have to worry about the order of the optional arguments in the function definition. Headers would be also smaller, easier to read, and easier to write. Pushing a bit further: (define (foo x y . rest) ....) would not accept keywords different from #:x and #:y, but (define (foo x y . rest-by-pos . rest-by-name) ....) would receive a list of positional argument values, and a dictionary of names and values, even if these names are not x or y. Laurent [1] http://msdn.microsoft.com/en-us/library/51wfzyw0.aspx [2] http://www.diveintopython.net/power_of_introspection/optional_arguments.html
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