Re: [eclipse-clp-users] List of Structures

Dear Joachim,

  As a matter of fact I have a template which is created out of Dbi library.
The result in my case is Result = [goodsinfo(101, "laptop"), goodsinfo(102, "notebook")].
Here I cannot declare the Template using { } brackets. The syntax is Template = goodsinfo(goodsid:10,goodsname:"dsad"),

session_sql_query(Session, Template, SQL, Cursor),
cursor_all_tuples(Cursor, Result),

filter(Result, goodsid > 101), % To be done

I have reached a stage where I can use the following 

findall(X,(member(X,Result),X=goodsinfo(102, _)),Sols),

to get Sols = [goodsinfo(102, "notebook")]. 
But I want to be able to use complex operators to filter the structure.

Thanks and Regards,
Shrirang Edgaonkar
________________________________________
From: Joachim Schimpf [jschimpf_at_coninfer.com]
Sent: 03 February 2015 03:34:49
To: eclipse-clp-users_at_lists.sourceforge.net
Subject: Re: [eclipse-clp-users] List of Structures

On 02/02/2015 06:55, Edgaonkar, Shrirang wrote:
>
> I have been working on the following problem for some time. I wish to filter the following List.
>
> :- local struct( goodsinfo( goodsid, goodsname, price, saledate, term, zaikoamount, registerdate,
> categoryid, searchViews ) ).
>
>
> Result = [goodsinfo(101, "laptop", "tablet", "iPad"), goodsinfo(102, "notebook", "pendrive", "tab")]
>

Your structure syntax is wrong.  You have declared a structure
goodsinfo/9 (i.e. with 9 arguments), but the example list contains
goodsinfo/4 structures.


Note that there are two ways to write structures in ECLiPSe:

1. Canonical (Prolog-style) notation:  This style can be used without
any preceding struct-declaration, and has the simple form

    functor_name(argument1, ..., argumentN)

i.e. you use *round* brackets and you must write *all* N arguments
in the correct order from 1 to N.  The arity of the structure is N.


2. ECLiPSe's struct-syntax:  This requires a preceding struct-declaration,
and has the form

    functor_name{arg_name:arg_value, ...}

i.e. you use *curly* brackets, and you label every argument with its declared
field name.  You do *not* have to write all N arguments, and you can write the
arguments in any order.  The system knows the arity and argument position from
the struct-declaration.

ECLiPSe basically macro-expands the f{...} syntax into f(...) syntax.  See how
it works by issuing your struct-declaration above, and trying a query like

?- X = goodsinfo{price:9.99, goodsname:"mouse"}.

X = goodsinfo(_275, "mouse", 9.99, _278, _279, _280, _281, _282, _283)
Yes (0.00s cpu)

You see that the convenient {}-syntax has been expanded into the internal form
with all 9 arguments, the price and goodsname arguments have been put into the
correct argument slots, and the remaining arguments filled with free variables.


>
> I am trying something like this
>
> (foreach(goodsinfo( goodsid:GoodsId, goodsname, term, searchViews ),Result), fromto(List,Out,In,[]) do
>     X[goodsid of goodsinfo] == 101 -> Out=[X|In] ; Out=In, writeln( X[goodsid of goodsinfo] )),

The loop structure is essentially correct.  The following would work:

filter101(Xs, Ys) :-
    ( foreach(X,Xs), fromto(Ys,Ys2,Ys1,[]) do
        ( goodsinfo{goodsid:101}=X -> Ys2=[X|Ys1] ; Ys2=Ys1 )

        %%% Alternatively:
        %%% ( X[goodsid of goodsinfo]=:=101 -> Ys2=[X|Ys1] ; Ys2=Ys1 )
        %%% Alternatively:
        %%% arg(goodsid of goodsinfo, X, I), (I==101 -> Ys2=[X|Ys1] ; Ys2=Ys1 )
    ).



-- Joachim





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