CODEWITHSUNDEEP
mathsyntaxprologaddition
oalsing
oalsing

Reputation: 100

Prolog `is` arithmetic failing strangely

The following code 

itD(Start, End, Distance, Max) :-
   Distance < Max,
   newDistance is Distance+1,
   itD(Start, End, newDistance, Max).

Gives me a very strange fail.

  2    2  Call: 0<15 ? 
  2    2  Exit: 0<15 ? 
  3    2  Call: newDistance is 0+1 ? 
  3    2  Fail: newDistance is 0+1 ?

Which I really don't understand. Since I'm using really basic arithmetics. 

| ?- Distance is 1, NewDistance is Distance+1.
  Distance = 1
  NewDistance = 2
  yes

As you can see I have no issues what so ever writing the same operation in the console.

I would be really glad if someone could help me figure this strange arithmetic issue.

Upvotes: 0

Views: 84

Answers (1)

oalsing
oalsing

Reputation: 100

Just the second after I posted this i realized that variables in prolog need to start with a capital letter, I guess that's a quite common mistake for someone new in Prolog.

Hope this will help someone out in the future.

Upvotes: 2

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