4.4BSD/usr/src/contrib/calc-1.26.4/help/variable

Variable declarations

	Variables can be declared as either being global or local.
	Global variables are visible to all functions and on the command
	line.  Local variables are visible only within a single function or
	command sequence.  When the function or command sequence returns,
	the local variables are deleted.

	To declare one or more variables, the 'local' or 'global' keywords
	are used, followed by the desired list of variable names, separated
	by commas.  The definition is terminated with a semicolon.  Examples
	of declarations are:

		local	x, y, z;
		global	fred;
		local	foo, bar;

	Within function declarations, all variables must be defined.
	But on the top level command line, assignments automatically define
	global variables as needed.  For example, on the top level command
	line, the following defines the global variable x if it had not
	already been defined:

		x = 7

	Variables have no fixed type, thus there is no need or way to
	specify the types of variables as they are defined.  Instead, the
	types of variables change as they are assigned to or are specified
	in special statements such as 'mat' and 'obj'.  When a variable is
	first defined using 'local' or 'global', it has the null type.

	If a procedure defines a local variable name which matches a
	global variable name, or has a parameter name which matches a
	global variable name, then the local variable or parameter takes
	precedence within that procedure, and the global variable is not
	directly accessible.

	There are no pointers in the calculator language, thus all
	arguments to user-defined functions are normally passed by value.
	This is true even for matrices, strings, and lists.  In order
	to circumvent this, the '&' operator is allowed before a variable
	when it is an argument to a function.  When this is done, the
	address of the variable is passed to the function instead of its
	value.  This is true no matter what the type of the variable is.
	This allows for fast calls of functions when the passed variable
	is huge (such as a large array).  However, the passed variable can
	then be changed by the function if the parameter is assigned into.
	The function being called does not need to know if the variable
	is being passed by value or by address.

	Built-in functions and object functions always accept their
	arguments as addresses, thus there is no need to use '&' when
	calling built-in functions.