Re: list comprehension patterns

[Per Bothner <per@bothner.com>]

On 05/19/2017 08:38 AM, Helmut Eller wrote:
> It would be nice to have some analog to Python's set and dictionary
> comprehension not just list comprehensions.

While Kawa has an OK hashtable API, I would like a more concise "map literal"
syntax, plus I'd like to be able to use a map as a function (i.e. using
funation call syntax, like Kawa allows for sequences).

Not sure how to do dictionary/map comprehensions but definitely worth thinking about.

I'm not convinced that set comprehensions are useful enough to be a priority.

> Maybe also a concise syntax
> way for things like "argmax".

Hm.  No brilliant ideas come to mind.  You could do something like:
(! mx (max @lst))
(! argmaxes ;; all max indexes
     (let (([i ...] [0 <: (length lst)]))
       [(if (= (lst i) mx) i) ...]))
(! argmax (argmaxes 0)) ;; first max index

That is obviously pretty klunky.
> In general, I'm disappointed that Kawa moves away from prefix notation
> (i.e. I will not use it these things).

If you're referring to the postfix '...' operator, that is a little non-Scheme-y - but
it is taken directly from R5RS syntax-rules.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/