[eclipse-users] simple_findall/2 example

From: Lutz, Charles D <charles.d.lutz_at_...53...>
Date: Tue, 08 May 2007 10:53:00 -0400
Hi ECLiPSe users,

 

I'm trying to understand the working of the simple_findall/2 example
shown in

section 4.4.1 of the Tutorial (v. 21 Apr 07).

 

Here is the simple_findall/2 example: 

 

%From section 4.4.1:

 

simple_findall(Goal, Solutions) :-

  bag_create(Bag),

  (

     call(Goal),

     bag_enter(Bag, Goal),

     fail

  ;

     bag_dissolve(Bag, Solutions)

  ).

 

Here is a run using it:

 

[eclipse 9]: simple_findall(member(1, [2, 3, 5, 1, 3, 6, 1, 1]), Solns).

 

Solns = [member(1, [2, 3, 5, 1, 3, 6, 1, 1]), member(1, [2, 3, 5, 1, 3,
6, 1, 1]

), member(1, [2, 3, 5, 1, 3, 6, 1, 1])]

Yes (0.00s cpu)

 

The interesting thing is how the solution set consists of the same thing
three times,

for the three times that the symbolic atom "1" appears in the list.

 

What I was unsure of was the use of the "fail" and how bag_enter/2
collects the

individual solutions.

 

The top "half" of the parenthesized disjunction is a conjuction with one
of the terms

being "fail". Shouldn't the whole conjuction fail, then? 

 

I read the help on bag_enter/2 and to be honest I didn't get much out of
it. There is

a main paragraph that discusses the unordered nature of the bag etc. It
ends with a

sentence that doesn't "click" for me: "In particular, if the term
contains variables,

they lose their identity and are replaced with fresh ones." What does
this say? :-)

 

Thanks in advance for any insight.

 

Chuck Lutz

Lockheed Martin

Systems of Systems Engineering

BMC4I Modeling and Simulation

Moorestown, NJ

(856)638-7234 (office)

charles.d.lutz@...53...

 

"A graphic is never an end in itself; it is a moment

in the process of decision making."
     - Jacques Bertin

 
Received on Tue May 08 2007 - 15:53:22 CEST

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