[m-dev.] alternative syntax for pred declarations.

[Andrew Bromage]

G'day.

Thomas Charles CONWAY wrote:

> It would be nice to be able to write:
>  
> :- type parser(T)	== pred(maybe(T), parse_state, parse_state).
> 
> :- mode parser		:: (pred(out, in, out) is det).
> 
> :- pred this_parser	= parser(xxx).
> :- mode this_parser	= parser.

I agree with Fergus that this is not quite the right syntax.

Since the current plan is to use ':' for type qualifiers and '::' for
mode qualifiers, so I guess it would make sense to use these here too:

:- pred this_parser : parser(xxx).
:- mode this_parser :: parser.

If we want to do currying:

:- pred match_token(token) : parser(unit).
:- mode match_token(in) :: parser is det.

The first declaration should be read, `the pred match_token(token) has
type parser(unit)'.

Alternatively, if you want to be more compact (and less legible):

:- pred match(token :: in) : (parser(unit) :: parser) is det.

Cheers,
Andrew Bromage