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Idiom #12 Check if list contains a value

Check if the list contains the value x.
list is an iterable finite container.

Is this x item contained in this list? 
return list.indexOf(x) !== -1;

Array.prototype.includes() is preferred but if you are supporting browsers that are 5+ years old, for example IE11, and you are not using a transpiler, then the old syntax with indexOf is generally well-understood.
return list.includes(x);

ES7 (Works on strings from ES6)
with Ada.Containers.Vectors;
Result := List.Contains (X);
New implementation...
< > ⌨
programming-idioms.org 
return list.indexOf(x) !== -1;
return list.includes(x);
Result := List.Contains (X);
bool contains(int x, int* list, size_t list_len) {
    for (int i=0 ; i<list_len ; i++)
        if (list[i] == x)
            return true;
    return false;
}
List.mem x list
(some (partial = x) list)
(some #{x} list)
bool Contains(const std::vector<int> &list, int x)
{
	return std::find(list.begin(), list.end(), x) != list.end();
}
auto contains(auto list, auto x) -> bool {
  return std::ranges::find(list, x) != std::ranges::end(list);
}
list.Contains(item);
bool here = canFind(items, x);
list.contains(x);
x in list
Enum.member?(list, x)
lists:member(X, List).
member(_, []) -> false;
member(Value, [H|_]) where Value =:= H -> true;
member(Value, [_|T]) -> member(Value, T).
member(_, []) -> false;
member(Value, [H|T]) -> 
  case H of
    Value -> true;
    _ -> member(T)
  end.
if (findloc (list, x, 1) != 0) then
if (any(x == list)) ...
slices.Contains(list, x)
func Contains(list []T, x T) bool {
	for _, item := range list {
		if item == x {
			return true
		}
	}
	return false
}
list.contains(x)
find _ [] = False
find n (x:xs)
  | x == n = True
  | otherwise = find n xs
x `elem` list
boolean contains(int[] list, int x){
  for(int y:list)
    if( y==x )
      return true;
  return false;
}
list.contains(x)
boolean <T> contains(T[] list, T x){
  if( x==null){
    for(T y:list)
      if( y==null )
        return true;
  }else{
    for(T y:list)
      if( x.equals(y) )
        return true;
  }
  return false;
}
asList(list).contains(x);
x in list
list.contains(x)
(find x list :test #'equal)
(member x list)
function contains(list, x)
	for _, v in ipairs(list) do
		if v == x then return true end
	end
	return false
end
[list containsObject:x];
in_array($x, $list, true);
result := false;
for e in list do 
	if e=x then
		begin
			result := true;
			break;
		end

result := list.IndexOf(x) <> -1;
p := list;
while (p <> nil) and (p^.key = x) do p := p^.next;
found := p.key = x
print "ok\n" if first {$_ eq $x} @list;
print "Found 'foo'\n" if grep {$_ eq $x} @list;
member(X, [One]).
x in list
list.include? x
(&list).into_iter().any(|v| v == &x)
list.contains(&x);
list.iter().any(|v| v == &x)
list.binary_search(&x).is_ok()
list.contains(x)

(member x list)
(define (contains list x)
	(cond [(null? list) #f]
		[(equal? (car list) x) #t]
		[else (contains (cdr list) x)]))
list includes: x.
List.Contains(x)