[mercury-users] Field updates and state variables

[Peter Hawkins]

Hi..
On Jul 2, 2006, at 7:26 PM, Peter Schachte wrote:

> On Sun, Jul 02, 2006 at 12:28:06PM -0700, Peter Hawkins wrote:
>> Hi...
>>
>> I find myself writing code like this a lot:
>> ...
>> !:S = !.S ^ my_map := map.insert(!.S ^ my_map, Key, Value)
>> ...
>>
>> Wouldn't it be nice if I could write the field update as:
>> map.insert(Key, Value, !S ^ my_map)
>
> That seems pretty magical; the former is not what I would naturally
> expect the latter to expand to.

Well, to be precise I actually meant it to expand to this:
map.insert(Key, Value, !.S ^ my_map, Temp),
!:S = !.S ^ my_map := Temp,

This hopefully is more obvious. I'm open to something like the elem  
trick --- I just want a little less typing for updating objects  
inside  state variables.

Cheers,
Peter

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