[mercury-users] Inst problem with hash tables

[andrea bini]

----- Messaggio Originale -----
Da: Ralph Becket <rafe at csse.unimelb.edu.au>
Data: Lunedi', Settembre 22, 2008 4:49 am
Oggetto: Re: [mercury-users] Inst problem with hash tables
A: mercury-users at csse.unimelb.edu.au

> What you need is something like this:
> 
> :- func unsafe_promise_unique_hash_table(hash_table(K, V)::in) = 
> 	(hash_table(K, V)::hash_table_uo) is det.
> 
> :- pragma foreign_proc("C",
> 	unsafe_promise_unique_hash_table(HT0::in) = (HT::hash_table_uo),
> 	[promise_pure, will_not_call_mercury],
> "
> 	HT = HT0;
> ").
> 
> I'm just testing a version of this which I've added to the hash_table
> module.  I'll let you know once it's been reviewed.

Using this function I get no compiling errors but I haven't managed to save and load a hash table anyway.
Consider this sample program:


main(!IO) :-
    % generate a list like this [{"a",1},{"b",2}, ... ]
    %
    different_strings(500,1,Strings),
    add_ints(Strings,0,IStrings),

    % the ht is filled from the list using strings
    % as keys and ints as values
    %
    new_default(string_double_hash) = Table,
    fill_table(IStrings,Table,Table1),

    % write hash table to disk
    %
    io.open_binary_output("ht.dat",Res1,!IO),
    (
      if
        Res1 = ok(HTdat)
      then
        io.write_binary(HTdat,Table1,!IO),
        io.close_binary_output(HTdat,!IO)
      else
        error("Cannot open ht.dat!")
    ),

    % reads the hash table back from disk and prints it
    %
    io.open_binary_input("ht.dat",Res2,!IO),
    (
      if
        Res2 = ok(HTdat2)
      then
        io.read_binary(HTdat2,ResTab,!IO),
        (
          if
            ResTab = ok(Table20)
          then
            unsafe_promise_unique_hash_table(Table20) = Table2,
            io.print(Table2,!IO)
          else
            error("Invalid ht.dat!")
        ),
        io.close_binary_output(HTdat2,!IO)
      else
        error("Cannot open ht.dat!")
    ).



It is compiled with no errors but when run it reports the error "Invalid ht.dat". I think that the problem resides in the high-order term in the hash table structure. It is written to disk just as the string '<<predicate>>'.

How can I fix this problem?

Thanks!
Cheers,

Andrea Bini



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