Re: new map type (Re: Ann: SWI-Prolog 7.1.0)

On 11/22/2013 07:00 PM, Alan Baljeu wrote:
>   - The system introduces `maps' as primary citizens.  Maps are
> 
>     collections of key-value pairs, optionally typed. Maps are
>     supported by read and write.  The syntax is
> 
>     type{key1:value1, key2:value2, ...}
> 
> 
> This will be very nice.  Incidentally in my project I have compiled 
> names into indices in class-generated objects, so I won't be needing
> the map for that.
>     Keys in a map can be addressed using the functional notation
>     Map.Key.  User functions on maps can be accessed as Map.Compound
>     (e.g., Vector.multiply(V2)).
> 
> 
> When you say functional notation, I am a little leary of confusion
> 
> regarding when something gets applied:
> plus(Map.key, 2,3) does this work?
> plus(Map.Key, 2,3) does this work?  Does it backtrack if Key is non-ground?

It is equivalent to

	get_map_ex(key, Map, V),
	plus(V, 2, 3).

(the _ex version raises an exception if key is not in Map).  This rewriting
is done by expand_goal/2.

> The notation Vector.multiply(V2) *might* be okay, but I'm skeptical.  I 

> suppose this implies:
> Vector  .multiply(V2) % good
> Vector.  multiply(V2) % error

I assume people will get used to that.

> But in any event, is there a meaning to this example, or is it a bad choice 
> of words?  The only thing I can think of is not very Prolog-like:
> 
> V2 = V1.scalar_multiply(3), or
> Number = Vector.dotProduct(V2)

Sorry, bad wording.

> Will/do other systems support maps?

I don't think it is my power to decide on that :-)  Vitor (YAP) will surely
consider this and I think is quite likely to follow.  Otherwise, I think the
`market' will decide.  Implementing all the changes was not a big deal.  If
people appreciate them in SWI-Prolog, I guess they will start asking the
other systems to consider this.  Then there could be small changes to the
various details to get a wider accepted implementation.  If you use these
features, you should be prepared to live with the idea that this might not
be the final word in all details.  I do not expect major changes from here.

	Cheers --- Jan