Prolog: Finding the Nth Element in a List

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Published on 2010-04-06T04:09:12Z Indexed on 2010/04/06 4:13 UTC
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I am attempting to locate the nth element of a List in Prolog. Here is the code I am attempting to use:

Cells = [OK, _, _, _, _, _] .

...

next_safe(_) :-
facing(CurrentDirection),
delta(CurrentDirection, Delta), 
in_cell(OldLoc), 
NewLoc is OldLoc + Delta,
nth1(NewLoc, Cells, SafetyIdentifier),
SafetyIdentifier = OK .

Basically, I am trying to check to see if a given cell is "OK" to move into. Am I missing something?

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