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(librep.info)Setting Variables

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Setting Variables
-----------------

   "Setting" a variable means to overwrite its current value (that is,
the value of its most recent active binding) with a new one. In the
variable-as-stack analogy, this is analogous to overwriting the top of
the stack. The old value is irretrievably lost (unlike when a new value
is bound to a variable, Note: Local Variables).

   The `setq' special form is the usual method of altering the value of
a variable.

 - Special Form: setq variable form ...
     Each VARIABLE is set to the result of evaluating its corresponding
     FORM. The last value assigned becomes the value of the `setq' form.

          (setq x 20 y (+ 2 3))
              => 5

     In the above example the variable `x' is set to `20' and `y' is
     set to the value of the form `(+ 2 3)' (5).

 - Function: set variable new-value
     The value of the variable VARIABLE (a symbol) is set to NEW-VALUE
     and the NEW-VALUE is returned.

     This function is used when the VARIABLE is unknown until run-time,
     and therefore has to be computed from a form.

          (set 'foo 20)
          ==
          (setq foo 20)           ;`setq' means `set-quoted'
              => 20

     _Note:_ currently the `set' function may be used to set any type
     of variable (i.e. lexical or special). However this likely to
     change in the future, such that only special variables will be
     allowed to be modified using the `set' function. It is strongly
     advised to avoid using this function on lexical bindings!
     (Moreover the compiler may generate incorrect code in certain
     circumstances.)