[e-lang] record syntax for E, please help

[Kevin Reid]

On Jan 7, 2008, at 19:56, Pierre Radermecker wrote:

> Does E provide syntactic facilities for "records" ? I like to do
> something similar to the Erlang record syntax :
>
> -record(language,{name = 'E', popularity= high, rating}).
>
> Declaring a constructor for each default/optional data does not sound
> like a practical option ;-) Is it the default way to create data  
> container ?
>
> I would like to have an immutable data store that can be built quickly
> according to the data at hand together with an explicit "template"  
> that
> indicate which kind of data the objects can hold. So "dictionary" or
> "map" seems like a poor option.
>
> Of course if I can do "pattern matching" (or whatever) to quickly
> create, read or update the container that would be wonderful.

Well, let's sketch something out. I've been thinking about a library  
to provide Haskell-style algebraic data types, which would need much  
of the same mechanism as this problem.

How would you like this?

? def [=> makeLanguage] := recordType`name :$String := ${"E"},
 >                                     popularity := $high,
 >                                     rating :$int`

(the := is used to match E's map-default syntax, which might change)

? def l := makeLanguage([name => "Java",
 >                        rating => 64])
# value: <language name => "Java", popularity => <high>, rating => 64>

? l.name()
# value: "Java"

? pragma.enable("call-pattern")
 > def makeLanguage([=> name, => rating] | _) := l
 > rating
# value: 64

Now, this might be a bit inefficient in current implementations  
(though maps in arguments really ought to be optimized, considering);  
one could instead pack it in the verb:

? def l := makeLanguage."name,rating"("Java", 64)
# value: <language name => "Java", popularity => <high>, rating => 64>

? def makeLanguage."popularity,rating"(p, r) := l
 > p
# value: <high>


What I'm intending to show is, there are ways to do this without  
extending the fundamental syntax. We just need to pick a good one.

What do you think? What would you prefer?

-- 
Kevin Reid                            <http://homepage.mac.com/kpreid/>