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早期freebsd实现

			CALC - An arbitrary precision calculator.
				by David I. Bell


	This is a calculator program with arbitrary precision arithmetic.
	All numbers are represented as fractions with arbitrarily large
	numerators and denominators which are always reduced to lowest terms.
	Real or exponential format numbers can be input and are converted
	to the equivalent fraction.  Hex, binary, or octal numbers can be
	input by using numbers with leading '0x', '0b' or '0' characters.
	Complex numbers can be input using a trailing 'i', as in '2+3i'.
	Strings and characters are input by using single or double quotes.

	Commands are statements in a C-like language, where each input
	line is treated as the body of a procedure.  Thus the command
	line can contain variable declarations, expressions, labels,
	conditional tests, and loops.  Assignments to any variable name
	will automatically define that name as a global variable.  The
	other important thing to know is that all non-assignment expressions
	which are evaluated are automatically printed.  Thus, you can evaluate 
	an expression's value by simply typing it in.

	Many useful built-in mathematical functions are available.  Use
	the 'show builtins' command to list them.  You can also define
	your own functions by using the 'define' keyword, followed by a
	function declaration very similar to C.  Functions which only
	need to return a simple expression can be defined using an
	equals sign, as in the example 'define sc(a,b) = a^3 + b^3'.
	Variables in functions can be defined as either 'global', 'local',
	or 'static'.  Global variables are common to all functions and the
	command line, whereas local variables are unique to each function
	level, and are destroyed when the function returns.  Static variables
	are scoped within single input files, or within functions, and are
	never destroyed.  Variables are not typed at definition time, but
	dynamically change as they are used.  So you must supply the correct
	type of variable to those functions and operators which only work
	for a subset of types.

	By default, arguments to functions are passed by value (even
	matrices).  For speed, you can put an ampersand before any
	variable argument in a function call, and that variable will be
	passed by reference instead.  However, if the function changes
	its argument, the variable will change.  Arguments to built-in
	functions and object manipulation functions are always called
	by reference.  If a user-defined function takes more arguments
	than are passed, the undefined arguments have the null value.
	The 'param' function returns function arguments by argument
	number, and also returns the number of arguments passed.  Thus
	functions can be written to handle an arbitrary number of
	arguments.

	The mat statement is used to create a matrix.  It takes a
	variable name, followed by the bounds of the matrix in square
	brackets.  The lower bounds are zero by default, but colons can
	be used to change them.  For example 'mat foo[3, 1:10]' defines
	a two dimensional matrix, with the first index ranging from 0
	to 3, and the second index ranging from 1 to 10.  The bounds of
	a matrix can be an expression calculated at runtime.

	Lists of values are created using the 'list' function, and values can
	be inserted or removed from either the front or the end of the list.
	List elements can be indexed directly using double square brackets.

	The obj statement is used to create an object.  Objects are
	user-defined values for which user-defined routines are
	implicitly called to perform simple actions such as add,
	multiply, compare, and print. Objects types are defined as in
	the example 'obj complex {real, imag}', where 'complex' is the
	name of the object type, and 'real' and 'imag' are element
	names used to define the value of the object (very much like
	structures).  Variables of an object type are created as in the
	example 'obj complex x,y', where 'x' and 'y' are variables.
	The elements of an object are referenced using a dot, as in the
	example 'x.real'. All user-defined routines have names composed
	of the object type and the action to perform separated by an
	underscore, as in the example 'complex_add'.  The command 'show
	objfuncs' lists all the definable routines.  Object routines
	which accept two arguments should be prepared to handle cases
	in which either one of the arguments is not of the expected
	object type.

	These are the differences between the normal C operators and
	the ones defined by the calculator.  The '/' operator divides
	fractions, so that '7 / 2' evaluates to 7/2. The '//' operator
	is an integer divide, so that '7 // 2' evaluates to 3.  The '^'
	operator is a integral power function, so that 3^4 evaluates to
	81.  Matrices of any dimension can be treated as a zero based
	linear array using double square brackets, as in 'foo[[3]]'.
	Matrices can be indexed by using commas between the indices, as
	in foo[3,4].  Object and list elements can be referenced by
	using double square brackets.

	The print statement is used to print values of expressions.
	Separating values by a comma puts one space between the output
	values, whereas separating values by a colon concatenates the
	output values.  A trailing colon suppresses printing of the end
	of line.  An example of printing is 'print \"The square of\",
	x, \"is\", x^2\'.

	The 'config' function is used to modify certain parameters that
	affect calculations or the display of values.  For example, the
	output display mode can be set using 'config(\"mode\", type)',
	where 'type' is one of 'frac', 'int', 'real', 'exp', 'hex',
	'oct', or 'bin'.  The default output mode is real.  For the
	integer, real, or exponential formats, a leading '~' indicates
	that the number was truncated to the number of decimal places
	specified by the default precision.  If the '~' does not
	appear, then the displayed number is the exact value.

	The number of decimal places printed is set by using
	'config(\"display\", n)'.  The default precision for
	real-valued functions can be set by using 'epsilon(x)', where x
	is the required precision (such as 1e-50).

	There is a command stack feature so that you can easily
	re-execute previous commands and expressions from the terminal.
	You can also edit the current command before it is completed.
	Both of these features use emacs-like commands.

	Files can be read in by using the 'read filename' command.
	These can contain both functions to be defined, and expressions
	to be calculated.  Global variables which are numbers can be
	saved to a file by using the 'write filename' command.