Re: Some advice on a "simple" thing...

Wow, I didn't realise how little I understood!

I am *guessing* now that by writing A=B in the list is the same as =(A,B)
and so in the code:

has_flag(NameFlags, Value, Name) :-
    member(Name=Mask, NameFlags),
    Value /\ Mask =\= 0.

It could be rewritten as:

has_flag(NameFlags, Value, Name) :-
     member(*=(Name, Mask)*, NameFlags),
    Value /\ Mask =\= 0.

at which point my brain goes, "Aha! It is *just* unification after all and
not magic".

Is that a correct intrepretation?  And why '=', is it the case that any
functor would have done, for example could I have as easily written this:

has_flag(NameFlags, Value, Name) :-
     member(*foo*(Name,Mask), NameFlags),
    Value /\ Mask =\= 0.

and this:

has_flag(NameFlags, Value, Name) :-
    member(*foo(Name, Mask)*, NameFlags),
    Value /\ Mask =\= 0.

Did you use '=' because it is builtin?? I am guessing I could use op() to
define my own, I will just for the hell of it and learn some more. (I
*will* try this but I am in work right now so I can't!) I think tonight I
advance my Prolog skills a little more. I will read LPN! on line about
functors. II left my Prolog books home this week!

Thanks once again for your time.

Sean.



On 9 April 2014 17:03, Daniel Diaz <[email protected]> wrote:

>  Le 09/04/2014 15:07, Sean Charles a écrit :
>
> Some clarificaation…. a while back you helped me write a testing
> framework…here is the code:
>
> get_all_tests(Tests) :-
> 	setof(Line-Name, get_one_test(Name, Line), Tests).
> get_one_test(Name, Line) :-
> 	current_predicate(Name/0),
> 	atom_concat('test_', _, Name),
> 	predicate_property(Name, prolog_line(Line)).	
>
>         It uses ‘pairs’ as I understand them, using the ‘-‘ to
>           combine the key and value, so in your response, what is ‘=‘
>           doing in this context in the list of flags????
>
>
>
>
>        There is no special meaning for '-' (except keysort/2 which sorts
> a list of pairs of the form Key-Value according to the Keys). In the above
> code
> I used a functor - but a = would work as well. We only need a structure to
> group 2 values (the functor does not care in this case).
>
> Daniel
>
>
>  Just when I thouthgh I was beginning to understand! LMAO
>
>  Thanks once again,
>
>  Sean.
>
>
>
>
>  On 9 Apr 2014, at 09:18, Daniel Diaz <[email protected]> wrote:
>
>  Hello Sean,
>
> you can do this with your own loop or use findall like this:
>
> flag(public, 0x0001).
>  flag(final, 0x0010).
>  flag(super, 0x0020).
>  flag(interface, 0x0200).
>  flag(abstract, 0x0400).
>  flag(synthetic, 0x1000).
>  flag(annotation, 0x2000).
>  flag(enum, 0x4000).
>
>
>  get_java_flags(Value, Flags) :-
>      findall(Name, has_flag(Value, Name), Flags).
>
>
> has_flag(Value, Name) :-
>     flag(Name, Mask),
>     Value /\ Mask =\= 0.
>
>
> then call it with:
>
> | ?- get_java_flags(0x421, Flags).
>
> Flags = [public,super,abstract]
>
> I have detailed a bit to be more comprehensive: the has_flag/2 predicate
> could be inlined inside the findall surrounding with ().
>
> If you prefer to have the flags as a parameter pass them as a list and use
> member to handle backtracking (done by get_flags/3 here):
>
> get_java_flags(Value, Flags) :-
>     FlagNames = [public = 0x0001,
>                 final = 0x0010,
>                 super = 0x0020,
>                 interface = 0x0200,
>                 abstract = 0x0400,
>                 synthetic = 0x1000,
>                 annotation = 0x2000,
>                 enum = 0x4000],
>     get_flags(FlagNames, Value, Flags).
>
>
>
> get_flags(FlagNames, Value, Flags) :-
>     findall(Name, has_flag(FlagNames, Value, Name), Flags).
>
> has_flag(NameFlags, Value, Name) :-
>     member(Name=Mask, NameFlags),
>     Value /\ Mask =\= 0.
>
>
> Daniel
>
> Le 09/04/2014 01:02, Sean Charles a écrit :
>
> Hello list,
>
>  I have almost completed a predicate called ‘jread’ which parses a Java
> .class file into a term that will allow me to create a database of all of
> the methods, fields, superclass and interfaces for that class and
> ultimately create a database for a complete “android.jar” file of any
> required API level.
>
>  I am, for educational purposes and my own learning, trying to build a
> system like Hoogle/Hayoo for Android. I do a lot of Android and I wanted to
> create a sytem I can wire into Emacs/IntelliJ or anything for that matter,
> a simple HTTP server that can supply a list of methods that have a certain
> type signature using a si mple query language.  Searching by types it very
> very useful when using Haskell and I wanted to improve my Prolog so I
> figured why not do something like that in GNU Prolog? I have already
> started a simple HTTP library in pure GNU Prolog as well but this comes
> first now.
>
>  Progress so far is good…if I run it like this from a folder containing
> the unpacked android.jar file...
>
>  | ?- jread('javax/net/SocketFactory.class',X).
>
>  X =
> javaclass(super('java/lang/Object'),class('javax/net/SocketFactory'),implements([]),
> methods([method(access_flags(4),name('<init>'),returns('()V'),[attr(9,
>
> [0,3,0,1,0,0,0,14,42,183,0,1,187,0,2,89,18,3,183,0,4,191,0,0,0,2,0,10,0,0,0,6,0,1,0,0,0
> ,4,0,
> 11,0,0,0,12,0,1,0,0,0,14,0,12,0,13,0,0])]),method(access_flags(41),name(getDefault)
> ,returns('()Ljavax/net/SocketFactory;'),a
> ttr(9,0,3,0,0,0,0,0,10,187,0,2,89,18,3,183,0,4,
>
> 191,0,0,0,1,0,10,0,0,0,6,0,1,0,0,0,5])]),method(access_flags(1),name(createSo
> cket),
>
> returns('()Ljava/net/Socket;'),[attr(9,0,3,0,1,0,0,0,10,187,0,2,89,18,3,183,0,4,191,
> 0,0,0,2,0,10,0,0,0,6,0,1,0,0,0,6,0
> ,11,0,0,0,12,0,1,0,0,0,10,0,12,0,13,0,0]),
> attr(18,0,1,0,19])]),method(access_flags(1025),name(createSocket),
> returns('(Ljava/
> lang/String;I)Ljava/net/Socket;'),[attr(18,[0,2,0,19,0,21])]),
> method(access_flags(1025),name(createSocket),
> returns('(Ljava/lang/String;ILjava/net/InetAddress;I)Ljava/net/Socket;’),
> [attr(18,[0,2,0,19,0,21])]),method(access_flags(1025),name(createSocket),
>
> returns('(Ljava/net/InetAddress;I)Ljava/net/Socket;’),[attr(18[0,1,0,19])]),method(access_flags(1025),name(createSocket),
> returns('(Ljava/net/InetAddress;ILjava/net/InetAddress;I)Ljava/net/Socket;'),[attr(18,[0,1,0,19])])]))
> ?
>
>  The place I am at now is decoding the bit flags for the class (and
> eventually the methods etc) into a term.
>
>  A typical value would be “1057” decimal, 0x421, this contains the flags:
>
>    ACC_PUBLIC 0x0001 Declared public; may be accessed from outside its
> package.  ACC_FINAL 0x0010 Declared final; no subclasses allowed.
> ACC_SUPER 0x0020 Treat superclass methods specially when invoked by the
> *invokespecial* instruction.  ACC_INTERFACE 0x0200 Is an interface, not a
> class.  ACC_ABSTRACT 0x0400 Declared abstract; must not be instantiated.
> ACC_SYNTHETIC 0x1000 Declared synthetic; not present in the source code.
> ACC_ANNOTATION 0x2000 Declared as an annotation type.  ACC_ENUM 0x4000 Declared
> as an enum type.
>
>  So you can see that 0x421 means “ACC_PUBLIC, ACC_SUPER and
> ACC_ABSTRACT”. I would like to produce a term something like this:
>
>      access_flags(public,super,abstract)
>
>  It’s not that I don’t know how to do it or that I can’t do it but I am
> not sure what is the *most elegant* way to do it in Prolog! Heaven knows I
> have written bit shifting loops to test for flags in a dozen languages but
> not in Prolog.
>
>  So, there’s the challenge, what is the most elegant way to turn a list
> of bits into a list of atom terms. Ideally I would make the list of atoms a
> parameter so that I can reuse it for the other flag based values.
>
>  Consider the gauntlet thrown!   In the meantime I am continuing to
> research the possibilities for myself. I will of course put it all on
> GitHub along with my Redis client. I may even create a Redis database with
> the information!
>
>  :)
> Sean.
>
>
>
>
> --
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>

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