Gamma: Version 4.0
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# Assignment Operators

Assignment Operators -- (`=`, `:=`, `::=`)

## Syntax

    symbol = s_exp
    symbol := s_exp
    symbol ::= s_exp

## Arguments

`symbol`

  Any valid symbol.

`s_exp`

  Any expression.

## Returns

The assigned value.

## Description

= is used to assign a value to a variable.

:= is used to assign a value only if no value is currently assigned to the `symbol`. If the `symbol` already has a value then the `symbol` keeps its original value.

::= is used to assign a constant. Once the assignment has been made no changes to the `symbol` are allowed. Attempted changes to the `symbol` will generate an error.

## Example

        Gamma> a = 5;
        5
        Gamma> a := 6;
        5
        Gamma> a;
        5
        Gamma> b ::= 7;
        7
        Gamma> b = 8;
        Assignment to constant symbol: b
        debug 1>
        Gamma> b ::= 9;
        Defvar of defined constant: b
        debug 1>
        Gamma>

## See Also

`defvar`

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