defmath function (actually a Lisp macro) is like
except that code in the body of the definition can make use of the full
range of Calculator data types. The prefix ‘calcFunc-’ is added
to the specified name to get the actual Lisp function name. As a simple
(defmath myfact (n) (if (> n 0) (* n (myfact (1- n))) 1))
This actually expands to the code,
(defun calcFunc-myfact (n) (if (math-posp n) (math-mul n (calcFunc-myfact (math-add n -1))) 1))
This function can be used in algebraic expressions, e.g., ‘myfact(5)’.
The ‘myfact’ function as it is defined above has the bug that an
expression ‘myfact(a+b)’ will be simplified to 1 because the
formula ‘a+b’ is not considered to be
posp. A robust
factorial function would be written along the following lines:
(defmath myfact (n) (if (> n 0) (* n (myfact (1- n))) (if (= n 0) 1 nil))) ; this could be simplified as: (and (= n 0) 1)
If a function returns
nil, it is left unsimplified by the Calculator
(except that its arguments will be simplified). Thus, ‘myfact(a+1+2)’
will be simplified to ‘myfact(a+3)’ but no further. Beware that every
time the Calculator reexamines this formula it will attempt to resimplify
it, so your function ought to detect the returning-
nil case as
efficiently as possible.
The following standard Lisp functions are treated by
~= is an abbreviation for
math-nearly-equal, which is useful in implementing Taylor series.
For other functions func, if a function by the name ‘calcFunc-func’ exists it is used, otherwise if a function by the name ‘math-func’ exists it is used, otherwise if func itself is defined as a function it is used, otherwise ‘calcFunc-func’ is used on the assumption that this is a to-be-defined math function. Also, if the function name is quoted as in ‘('integerp a)’ the function name is always used exactly as written (but not quoted).
Variable names have ‘var-’ prepended to them unless they appear in
the function's argument list or in an enclosing
or their names already contain a ‘-’ character. Thus a reference to
‘foo’ is the same as a reference to ‘var-foo’.
A few other Lisp extensions are available in
eltfunction accepts any number of index variables. Note that Calc vectors are stored as Lisp lists whose first element is the symbol
vec; thus, ‘(elt v 2)’ yields the second element of vector
v, and ‘(elt m i j)’ yields one element of a Calc matrix.
setqfunction has been extended to act like the Common Lisp
setffunction. (The name
setfis recognized as a synonym of
setq.) Specifically, the first argument of
setqcan be an
cdrform, in which case the effect is to store into the specified element of a list. Thus, ‘(setq (elt m i j) x)’ stores ‘x’ into one element of a matrix.
forlooping construct is available. For example, ‘(for ((i 0 10)) body)’ executes
bodyonce for each binding of ‘i’ from zero to 10. This is like a
letform in that ‘i’ is temporarily bound to the loop count without disturbing its value outside the
forconstruct. Nested loops, as in ‘(for ((i 0 10) (j 0 (1- i) 2)) body)’, are also available. For each value of ‘i’ from zero to 10, ‘j’ counts from 0 to ‘i-1’ in steps of two. Note that
forhas the same general outline as
let*, except that each element of the header is a list of three or four things, not just two.
foreachconstruct loops over elements of a list. For example, ‘(foreach ((x (cdr v))) body)’ executes
bodywith ‘x’ bound to each element of Calc vector ‘v’ in turn. The purpose of
cdrhere is to skip over the initial
vecsymbol in the vector.
breakfunction breaks out of the innermost enclosing
foreachloop. If given a value, as in ‘(break x)’, this value is returned by the loop. (Lisp loops otherwise always return
returnfunction prematurely returns from the enclosing function. For example, ‘(return (+ x y))’ returns ‘x+y’ as the value of a function. You can use
returnanywhere inside the body of the function.
Non-integer numbers (and extremely large integers) cannot be included
directly into a
defmath definition. This is because the Lisp
reader will fail to parse them long before
defmath ever gets control.
Instead, use the notation, ‘:"3.1415"’. In fact, any algebraic
formula can go between the quotes. For example,
(defmath sqexp (x) ; sqexp(x) == sqrt(exp(x)) == exp(x*0.5) (and (numberp x) (exp :"x * 0.5")))
(defun calcFunc-sqexp (x) (and (math-numberp x) (calcFunc-exp (math-mul x '(float 5 -1)))))
Note the use of
numberp as a guard to ensure that the argument is
a number first, returning
nil if not. The exponential function
could itself have been included in the expression, if we had preferred:
‘:"exp(x * 0.5)"’. As another example, the multiplication-and-recursion
myfact could have been written
:"n * myfact(n-1)"
A good place to put your
defmath commands is your Calc init file
(the file given by
~/.emacs.d/calc.el), which will not be loaded until Calc starts.
If a file named .emacs exists in your home directory, Emacs reads
and executes the Lisp forms in this file as it starts up. While it may
seem reasonable to put your favorite
defmath commands there,
this has the unfortunate side-effect that parts of the Calculator must be
loaded in to process the
defmath commands whether or not you will
actually use the Calculator! If you want to put the
commands there (for example, if you redefine
to be .emacs), a better effect can be had by writing
(put 'calc-define 'thing '(progn (defmath ... ) (defmath ... ) ))
put function adds a property to a symbol. Each Lisp
symbol has a list of properties associated with it. Here we add a
property with a name of
thing and a ‘(progn ...)’ form as
its value. When Calc starts up, and at the start of every Calc command,
the property list for the symbol
calc-define is checked and the
values of any properties found are evaluated as Lisp forms. The
properties are removed as they are evaluated. The property names
thing) are not used; you should choose something like the
name of your project so as not to conflict with other properties.
The net effect is that you can put the above code in your .emacs file and it will not be executed until Calc is loaded. Or, you can put that same code in another file which you load by hand either before or after Calc itself is loaded.
The properties of
calc-define are evaluated in the same order
that they were added. They can assume that the Calc modules calc.el,
calc-ext.el, and calc-macs.el have been fully loaded, and
that the ‘*Calculator*’ buffer will be the current buffer.
calc-define property only defines algebraic functions,
you can be sure that it will have been evaluated before Calc tries to
call your function, even if the file defining the property is loaded
after Calc is loaded. But if the property defines commands or key
sequences, it may not be evaluated soon enough. (Suppose it defines the
tweak-calc; the user can load your file, then type
M-x tweak-calc before Calc has had chance to do anything.) To
protect against this situation, you can put
at the end of your file. The
calc-check-defines function is what
looks for and evaluates properties on
has the advantage that it is quietly ignored if
is not yet defined because Calc has not yet been loaded.
Examples of things that ought to be enclosed in a
define-key calls that modify
the Calc key map, and any calls that redefine things defined inside Calc.
defuns need not be enclosed with