Re: "dict"ionary typing?

>  One

> might reasonably use append/3 as a function in three different modes.  I
> haven't implemented it yet, but I'm considering a new feature for
> library(func) inspired by Ciao's notation.  Specifically, a single ~ marks
> the argument to be used as output for *this* call.
> 
>  ?- writeln(append([a,b],[c,d],~)).


Regrettably every practical character is available
for use in terms, except those few reserved by the 
language itself.  This is why I've been advocating that
if we do introduce new syntax, it ought to be optional
so we can still do as you write above.