Interfaces / data types in E

We've got quite a few methods that take or return maps. e.g.

to purchase(customerDetails :Map[String,any]) {
   ... customerDetails["name"] ...
   ...
   if (problem) {
     notify(customerDetails["email"])
   }
   ...
}

The problem is that it's not obvious from the method signature what keys 
need to be present. Often someone fails to include a mapping, and the 
system only fails later in some case where it needed that value.

What I think I'd like to do is something like:

def CustomerDetails := makeNamedTuple([
	"name" => String,
	"email" => String,
])

...

to purchase(customerDetails :CustomerDetails]) {
   ... customerDetails["name"] ...
}

So that:

- if the caller fails to provide "name" and "email" then it fails the guard
- if I try to access a field I didn't define (e.g. "fax") then I get an 
error, whether or not the client provided it, so I'm forced to keep the 
interface up-to-date

Ideally it should handle fields being added later (e.g. if two parties 
are running different versions of the software it should ignore fields 
it doesn't understand).

Any ideas on the best way to do this? Maps? TermTrees?

Some of the other systems using this are written in Java, so ideally it 
should be easy to use from there too.


-- 
Dr Thomas Leonard
IT Innovation Centre
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Southampton SO16 7NS, UK


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