Re: A problem in program

[Gregory Bourassa]

Yang,

I assume you do know that the token, first, cannot be treated as a variable 
because it 
starts with a lowercase letter.

If you want to get the list's first element into a variable named "First",  the 
initial 
letter must be a capital as in:

    L = [First|_],
    write('first = '),write(First),nl,

The token, first,  is seen by Prolog as a symbol atom, not a variable.

Regards.

Gregory Bourassa


On Oct 23, "=?gb2312?B?1dTR9A==?=" <address@hidden> wrote:
Hi, all:
    Now I encounter a problem in programming. Consider the follow program.
    
q :-.......    
    solve_propagate(L,Line1,Line2),!,
    write('propagate success!'),nl,
    L = [first|_],
    write('first = '),write(first),nl,
    stato_img(CL,CLine1,CLine2,first),
    ......

    the first call solve_propagate() has bound the L, Line1, Line2(they are all 
list). I 
want get the fisrt element of L (variable first) and use to in the next call 
stato_img
(). But it does not work. The program stops at L = [first|_] and gives a 
warning "user 
directive failed". 
    I want to know what the problem is and how to solve it. Thank you!
 

Zhao, Yang
2006-10-23
 
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