[mercury-users] Feature request: State Variables + Data Terms

[obo at ruk.cuni.cz]

Hi.

I've fallen in love with the state variables syntax. But falling in love
with something also means that one often wishes to improve the object...

Would it be hard to allow syntax like this:

:- type my_data ---> data( foo::string, bar::int ).

:- pred update(my_data::in, my_data::out) is det.

update(!Data) :-
  add_one_to_int(!Data^bar).

...the semantics would be:

update(Data0, Data1) :-
  add_one_to_int(Data0^bar, TInt),
  Data1 = Data0^bar:=TInt.

I do not see any problem in another extra feature, using more than one
part of the dataterm at the same time:

update(!Data) :-
  add_one_to_int_and_trim_a_string(!Data^bar, !Data^foo).

How deep in your todo list would this wish sink?

Thanks, Andrew.

--
Ondrej Bojar (mailto:obo at cuni.cz)
http://www.cuni.cz/~obo


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