Calc - an RPN calculator for the Julia REPL

This Julia package implements an RPN calculator for use at the Julia command line (the REPL). The reverse-polish notation is popular with some scientific calculators. See the HP 48 for example.

This package enables a new REPL mode. Use the equals key (=) at the start of a line to start the calculator. RPN commands operate on a stack that is redisplayed after every operation. Use Backspace at a blank prompt to return to the normal Julia prompt.

The calculator keys tend to match that of Emacs Calc. See the following for a handy cheat sheet in several formats:

• https://github.com/SueDNymme/emacs-calc-qref/releases

Not all of the Emacs Calc operations are supported, but many basic arithmetic operations are supported.

By default, trig operations are entered and displayed in degrees. This setting can be changed with m r for radians and m d for degrees. Another setting controls display of complex numbers. The default display is in rectangular coordinates. Use m p to toggle between polar and rectangular coordinates.

This calculator also supports algebraic entry (normal Julia syntax). Within the calc> prompt, use = to switch to algebraic entry. This is useful for evaluating expressions that are difficult with the default Calc.jl keys. Examples include:

• Using a function that doesn't have a key defined.
• Entering a Julia variable onto the stack.
• Entering a negative number (= -23 is an alternative to 23 n).

With algebraic entry, you can refer to stack variables with _1, _2, _3, and so on.

Predefined Keys

In the following, x is the top value on the stack, and y is the second value on the stack.

Many multi-key sequences start with prefixes with the following meanings:

prefix	meaning
I	Inverse
H	Hyperbolic (other uses too)
f	Function
m	Mode
u	Statistics
s	Store

General

key	operation
<space>	Enter value on the stack
<enter>	Enter value on the stack
<del>	Delete x from the stack
<tab>	Swap x & y on the stack
U	Undo
D	Redo
=	Trigger algebraic entry
<backspace>	Exit the calculator

Arithmetic

key	operation
+	y + x
-	y - x
n	-x, negate
*	y * x
/	y / x
&	1/x
%	y % x, remainder
A	abs(x)
fs	sign(x)
fn	min(y, x)
fx	max(y, x)
f[	x - 1
f]	x + 1

Algebraic

key	operation
Q	sqrt(x)
IQ	x^2
L	log(x)
E	exp(x)
IL	exp(x)
HL	log10(x)
IHL	10^x
B	log(x, y)
^	y^x
I^	y^(1/x)
fh	sqrt(x^2 + y^2)

Trig

These trig functions use radian equivalents when in radian mode.

key	operation
S	sind(x)
C	cosd(x)
T	tand(x)
IS	asind(x)
IC	acosd(x)
IT	atand(x)
P	Insert π

Settings

key	operation
mr	Use radians
md	Using degrees
mp	Toggle between polar and rectangular coordinates

Complex numbers

key	operation
X	complex(y, x)
IX	the real and imaginary parts of x
Z	y∠x, polar entry with x in degrees
IZ	the magnitude and angle of x
J	conj(x)
G	angle(x)
fr	real(x)
fi	imag(x)

Percentages

key	operation
<meta-%>	x/100, convert from a percentage
c%	100x, convert to a percentage
b%	100(x-y)/y, percent change from y to x

Vectors

key	operation
|	vcat(y, x)
Vu	Unpack x to the stack
Vp	Pack the stack into a vector

Statistics

key	operation
u#	length(x)
u+	sum(x)
u*	prod(x)
uX	maximum(x)
uN	minimum(x)
uM	mean(x)
HuM	median(x)
uS	std(x)
HuS	var(x)

Storing

key	operation
ss	Store x in the prompted variable
sS	Store the whole stack in the prompted variable
<meta-k>	Copy x to the clipboard
<ctrl-k>	Pop x to the clipboard

Defining keys

Keys can be defined or redefined with Calc.setkeys by passing a keymap dictionary. Here is an example to map the key sequence fp to an operation that finds the parallel combination of impedances of the first two arguments on the stack:

Calc.setkeys(Dict("fp" => Calc.calcfun((y, x) -> 1 / (1/y + 1/x), 2)))

Calc.calcfun is the main function for defining operations. The first argument is the function that performs the operation, and the second argument is the number of arguments to that function. Neither Calc.setkeys nor Calc.calcfun are exported.