Info Catalog eintr: Using set eintr: set & setq eintr: Counting

eintr: Using setq

 
 1.9.2 Using ‘setq’
 ------------------
 
 As a practical matter, you almost always quote the first argument to
 ‘set’.  The combination of ‘set’ and a quoted first argument is so
 common that it has its own name: the special form ‘setq’.  This special
 form is just like ‘set’ except that the first argument is quoted
 automatically, so you don’t need to type the quote mark yourself.  Also,
 as an added convenience, ‘setq’ permits you to set several different
 variables to different values, all in one expression.
 
    To set the value of the variable ‘carnivores’ to the list ‘'(lion
 tiger leopard)’ using ‘setq’, the following expression is used:
 
      (setq carnivores '(lion tiger leopard))
 
 This is exactly the same as using ‘set’ except the first argument is
 automatically quoted by ‘setq’.  (The ‘q’ in ‘setq’ means ‘quote’.)
 
    With ‘set’, the expression would look like this:
 
      (set 'carnivores '(lion tiger leopard))
 
    Also, ‘setq’ can be used to assign different values to different
 variables.  The first argument is bound to the value of the second
 argument, the third argument is bound to the value of the fourth
 argument, and so on.  For example, you could use the following to assign
 a list of trees to the symbol ‘trees’ and a list of herbivores to the
 symbol ‘herbivores’:
 
      (setq trees '(pine fir oak maple)
            herbivores '(gazelle antelope zebra))
 
 (The expression could just as well have been on one line, but it might
 not have fit on a page; and humans find it easier to read nicely
 formatted lists.)
 
    Although I have been using the term “assign”, there is another way of
 thinking about the workings of ‘set’ and ‘setq’; and that is to say that
 ‘set’ and ‘setq’ make the symbol _point_ to the list.  This latter way
 of thinking is very common and in forthcoming chapters we shall come
 upon at least one symbol that has “pointer” as part of its name.  The
 name is chosen because the symbol has a value, specifically a list,
 attached to it; or, expressed another way, the symbol is set to point to
 the list.
 

Info Catalog eintr: Using set eintr: set & setq eintr: Counting