[mercury-users] partial instantiation?

[Ondrej Bojar]

Hi,

Tomas By wrote:
> I'd be interested in ideas about how to do this in Mercury. My only
> absolute requirement is that the list of commands (e.g. cmd/3) must be
> short and simple.

How about this:

:- type argtype ---> i; s.
:- type argdesc == list(pair(int, argtype)).
:- type cmd --->
           run(int, string)
         ; do(string).


:- pred cmd(string, argdesc, cmd).
:- mode cmd(out, out, out) is multi.
:- mode cmd(in, out, out) is semidet.

cmd("hi", [[], [2-s], [1-i]], run(0, "filename")).
% you may list the different shortcut calls on separate lines

:- func interpret(list(string)) = cmd.
interpret(Args, Replacements) :-
   if Args = [CmdName | CmdArgs]
   then
     (
     if cmd(CmdName, ArgDesc, CmdDefault)
     then
       type_to_term(Cmd, CmdTerm),
       % now replace the corresponding default values with what's given in
       % CmdArgs, interpreted using ArgDesc; check for errors (user supplies
       % string where int is expected..., nonexisting file given where existing
       % one is expected (the good thing is that you may support more types
       % on the user's side

       % finish with
       %   try_term_to_type(ReplacedTerm, MayCmd),
       %   (
       %   MayCmd = error(E),
       %     ...
       %   ;
       %   MayCmd = ok(Cmd)
       %   )
     else ...
   else % no cmd given
     ...

Cheers, Ondrej.

> 
> /Tomas
> 
> 
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-- 
Ondrej Bojar (mailto:obo at cuni.cz / bojar at ufal.mff.cuni.cz)
http://www.cuni.cz/~obo
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