Re: Ann: URI quasiquotes library

On 07/09/2013 12:17 PM, Michael Hendricks wrote:
> On Mon, Jul 8, 2013 at 9:56 AM, Jan Wielemaker <[email protected]

> I agree that functional notation is convenient.  The packs library(func)
> <http://www.swi-prolog.org/pack/list?p=func> and
> library(function_expansion)
> <http://www.swi-prolog.org/pack/list?p=function_expansion> are two of my
> favorites.

There is a long history of functional notation libraries in Prolog:
your two, GRIPS (by Jocelyn Paine), Ciao, are just a few I'm aware of.
Would be nice if the Prolog community could come to some form of
agreement here :-(

>     However, this functional notation need not be readable for
>     the user.  Possibly we should introduce a functional notation
>     library that does not affect normal Prolog syntax, but can be
>     enabled by default.  Something like '$EVAL'(Term).
>
>
> How do you imagine '$EVAL'(Term) behaving?  What kind of Term values are
> allowed?  One of the most common patterns I use with
> library(function_expansion) is to treat this:
>
>      foo('$EVAL'(Term))
>
> as if the code were this:
>
>      call(Term, Output),
>      foo(Output)
>
> Is that what you have in mind?

Yes.  For every goal, find the embedded '$EVAL'(Term),
and insert goals before it that evaluate them.  Quasi
quotations seem to come in some forms:

   - Those that describe a goal.  For example, {|sql||Query|}
     can expand into a call to odbc_query/3.
   - Those that describe data that is intended for a specific
     predicate.  Here, we can simply insert the qq into the
     proper argument location and the predicate can be designed
     to deal with the QQ result term.
   - Those that describe more or less generic data structures
     that can be passed to many predicates.  Your uri example
     is one of them.  You want to think about {|uri||...|} as
     an atom/string, but in fact it produces something that
     must be processed before it creates an atom/string at
     runtime.  You would like to be able to hide this processing
     from the user.  Else you need to write this, which removes
     most of the fun.

	expand_uri({|uri||....|}, Var),
	something(Var),
	...

So, for qq we can get away with a functional notation that uses
an unlikely and verbose term because it only needs to be entered
once when defining the QQ.

	Cheers --- Jan