Use an equal sign to assign values to variables.
i1 : x = "abcde"
o1 = abcde
|
i2 : x
o2 = abcde
|
Before assignment, any reference to a variable provides the symbol with that name. After assignment, the assigned value is provided. The variable created is global, in the sense that any code placed elsewhere that contains a reference to a variable called
x will refer to the one we just set.
It is important to distinguish between a symbol and its value. The initial value of a global symbol is the symbol itself, and the initial value of a local variable is
null. One possibility for confusion comes from the possibility of having a symbol whose value is another symbol; it's even more confusing if the two symbols have the same name but different scopes, for example, if one of them is global and the other is local.
i3 : y
o3 = y
o3 : Symbol
|
i4 : y = z
o4 = z
o4 : Symbol
|
i5 : y
o5 = z
o5 : Symbol
|
i6 : z = 444
o6 = 444
|
i7 : z
o7 = 444
|
i8 : y
o8 = z
o8 : Symbol
|
In the example above, the final value of
y is the symbol
z, even though the symbol z has acquired a value of its own. The function
value can be used to get the value of a symbol.
The operator
<- can be used to set the value of a symbol. This operator differs from
= in that the symbol or expression on the left hand side is evaluated.
i10 : y <- 555
o10 = 555
|
i11 : y
o11 = z
o11 : Symbol
|
i12 : z
o12 = 555
|
i13 : y = 666
o13 = 666
|
i14 : y
o14 = 666
|
i15 : z
o15 = 555
|
One reason the user needs to understand this concept is that assignments with the operator
<- are occasionally done on the user's behalf by bits of code already in the system, for example, when creating a polynomial ring the prospective variables are given new values that are the generators of the polynomial ring.