[Nick]

Hello guys,

I want to make a foreach loop where every time i will decrease the value of a variable.

For example:

foreach Counter = std::downTo(2,0) do

if Money > 100 then
Money = Money - 10
end if
end foreach


Any proposals please ??

[Ferenc Nagy]

foreach Counter = std::downTo(2,0) do

if Money > 100 then
Money = Money - 10
end if
end foreach

Nick,
In your above trial

Code: Select all

Money = Money - 10

always fails.

A) Use a fact variable instead of it in lower case.

Code: Select all

facts
money:integer.

in the clauses

...

Code: Select all

money:=IniMoneyValue,
foreach Counter = std::downTo(2,0) do
if money > 100 then
money := money - 10
end if
end foreach 

B) Use varM

Money=varM::new("")

Code: Select all

Money::new(IniMoneyValue),
foreach Counter = std::downTo(2,0) do
if Money:value() > 100 then
Money:value := Money:value() - 10
end if
end foreach 

Take care!
Left := Right is the "set value to the left side" operator,
Left = Right sets the value to the free side of the other is bound. If both sides are bound the '=' operators checks their equality.

[Nick]

thanks guys .... i'm kind new user :)

[Thomas Linder Puls]

Actually, you should avoid using that kind of imperative programming in Prolog. In Prolog variables are like variables in mathematics: in its scope a variable has one and only one value, the value does not change as result of computation.

As Ferenc Nagy describes, it is possible to apply such methods, but this should not be your standard way of programming. In Prolog you should in general use recursion instead of looping and you should in general use Green immutable variables in favour of black mutable fact variables in your algorithms. The black mutable fact variables should be used to represent the state of your system, not as temporaries in algorithms.

Your code could look like this:

Code: Select all

predicates
    strangeCalculation : (positive Counter, integer StartMoney) -> integer Money.
clauses
    strangeCalculation(Counter, StartMoney) = Money :-
        if 0 = Counter then
            Money = StartMoney
        else
            Money = strangeCalculation(Counter-1, StartMoney-10)
        end if.

Instead of updating variables and looping, we make a recursive invocation of the predicate (corresponding to the next iteration in the loop).