PrependTo

PrependTo(s, item)

prepend item to value of s and sets s to the result.

Assign s to a list

>> s = {1, 2, 4, 9}
{1,2,4,9}

Add a new value at the beginning of the list:

>> PrependTo(s, 0)
{0,1,2,4,9}

The value assigned to s has changed:

>> s
{0,1,2,4,9}

PrependTo works with a head other than List:

>> y = f(a, b, c)
>> PrependTo(y, x)
f(x,a,b,c)

>> y
f(x,a,b,c)

{a, b} is not a variable with a value, so its value cannot be changed.

>> PrependTo({a, b}, 1)
PrependTo({a,b},1)

a is not a variable with a value, so its value cannot be changed.

>> PrependTo(a, b)
PrependTo(a,b)

>> x = 1 + 2
3

Nonatomic expression expected at position 1 in PrependTo

>> PrependTo(x, {3, 4})
PrependTo(x,{3,4})