[ library(lists) | Reference Manual | Alphabetic Index ]

# delete(?Element, ?List1, ?List2)

Succeeds if List2 is List1 less an occurence of Element in List1.
?Element
Prolog term.
?List1
List or variable.
?List2
List or variable.

## Description

Unifies the list List2 with the list List1 less an occurence of Element. Any alternative solutions are provided on backtracking.

This predicate can be used to select an element from a list, delete an element or insert it.

The definition of this Prolog library predicate is:

delete(A, [A|B], B).
delete(A, [B, C|D], [B|E]) :-
delete(A, [C|D], E).
This predicate does not perform any type testing functions.

### Modes and Determinism

• delete(+, +, -) is nondet
• delete(-, +, -) is nondet
• delete(-, -, -) is multi

### Fail Conditions

Fails if List2 does not unify with List1 less an occurence of Element.

Yes.

## Examples

Success:
[eclipse]: delete(X,[1,M,X],L), writeln((M,X,L)), fail.
_g66 , 1 , [_g66, 1]
_g66 , _g66 , [1, _g66]
_g66 , _g72 , [1, _g66]
no (more) solution.

[eclipse]: delete(3,[1,3,5,3],L).
L = [1, 5, 3]    More? (;)
L = [1, 3, 5]
yes.

[eclipse]: delete(X,L,[a,b]), writeln((X,L)), fail.
_g66 , [_g66, a, b]
_g66 , [a, _g66, b]
_g66 , [a, b, _g66]
no (more) solution.

delete(X,[1,2],L).   (gives X=1 L=[2]; X=2 L=[1]).
Fail:
delete(1,[1,2,1,3],[2,3]).

## See Also

subtract / 3, member / 2