[mercury-users] Records

[Robert Ernst Johann JESCHOFNIK]

On Tue, 2 Nov 1999, Simon Taylor wrote:

Hello.

> :- type t
> 	---> t(
> 		field1 :: int,
> 		field2 :: string,
> 		field3 :: t2
> 	).

This is just my opinion, but I think it may be a bit clearer if the type
were to come before the field name,

:- type t --->
	t(
	   int    :: field1,
	   string :: field2,
	   t2     :: field3
	).

etc.

> 	% field extraction.
> 	Field1 = X ^ field1,		% Field1 = 1.
> 	Field5 = X ^ field3 ^ field5,	% Field5 = 'y'.

'^' doesn't really make me thing of anything associated with "lookup".
Would it be possible to use "->", or would that cause ambiguities with the
if-then-else syntax?

	Field1 = X->field1

does seem a tad `better', though.

Or even better, why not use the same symbol as is used for construction?

	Field1 = X::field1

> 	% field update.
> 	X1 = X0 ^ field1 := 2,		% X1 = t(2, "abc", t2(1.5, 'y')).
> 	X = X1 ^ field3 ^ field5 := 'z'.
> 					% X2 = t(2, "abc", t2(1.5, 'z')).

Perhaps here would be a good place for the '->'..

	X1 = X0::field1 -> 2,
	X = X1::field3::field5 -> 'z'.


> % DCG example:
> :- pred bar(t::in, t::out) is det.
> bar -->
> 	Field1 := ^ field1,
> 	Field5 := ^ field3 ^ field5,
> 
> 	^ field1 := 2,
> 	^ field3 ^ field5 := 'z'.

bar -->
	Field1 -> ::field1,
	Field5 -> ::field3::field5,

	::field1 -> 2,
	::field3::field5 -> 'z'.


I think either way it looks pretty ugly in a DCG.. but I can't really
think of any way to remedy this.


Ah well, just my proverbial two cents worth.


Rob
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