ERPN

An RPN calculator written in Python

The goal is to create a calculator that has a much easier and more usable interface for "live" use than dc.

It's keyboard based, for fast use.

There is always a quick reference of the availble functions, so you can use it for tasks you don't do every day.

It has strong undo functions and a clear overview of what is going on, so you don't lose time on typos and mistakes.

Instalation on Linux

This will install erpn for the current user only.

Make sure $/.local/bin/ is in your PATH. Run pip install --user erpn

Instructions

If you don't know what an RPN calculator is, you will probably need to find that out first. You can find a tutorial here: http://linuxfocus.org/~guido/hp_calc/handbooks/rpn-tutorial.html

This calculator only uses floating point numbers. This means there is a limit to how precise a number can be, and also how large or small it can be. The program will show an error if you try to go out of bounds.

To start number entry, simply start entering it using 0-9 or ..

To enter a negative number, you can start entry with an underscore (_). This will be converted to a "-" in the interface.

You can enter a number with an exponent. So for example 0.1e-4.

Some of the keys in the sidebar as listed "meta" something. Some people call that key "Alt" instead.

meta p and meta e are used to enter pi (3.14...) and e (eulers constant, 2.718...) onto the stack.

Display options

Using D you can enter the display menu. You can exit it by pressing D again, or by pressing enter.

There are a few options for display modes here.

Default display (d) tries to show the number without an exponent. It only displays an exponent when it needs to, either because the number can't be accurataly displayed without an exponent or because it would be too long.

Scientific Format (s) always shows an exponent, so you could have 1e2.

Engineering Format (e) is the same as scientific format, except the exponent is always a multiple of 3. So for example 100e6.

No Exponent (p) Never show an exponent. Example: 0.000.

You can change the precision usin + and -.

Copy and Paste

Within the stack

To copy the top value in the stack use space or enter.

You can move a marker up and down using the arrows (or the j and k keys). You can then use enter or space to copy that value to the end of the stack, or you can run most functions to first copy the selected item to the end of the stack and then run the function.

From the OS

You can copy to the OS (so you can use the results of your calculation elsewhere) using the c button. It will be formatted without regard to the current display settings.

To paste a value from the OS you use the p button.

Functions

Addition

Bound to +. Calculates x+y.

If there is nothing in the stack, it will return a default value of 0.

Ceiling

Bound to ~. Rounds x up to the first larger integer.

Delete

Bound to x. Removes item x from the stack.

If the arrow is pointing at something, delete that instead of item x.

Divide

Bound to /. Calculates y/x.

Dividing by 0 will result in an error, values like inf are not supported by erpn.

Exponent

Bound to p (p for power). Calculates y^x.

Factorial

Bound to !. Calculates x!, i.e. x*(x-1)(x-2)...21.

Floor

Bound to ` (backtick). Rounds x down to the first smaller integer.

GCD (Greatest common divisor)

Bound to #. Calculates the largest integer divisor of both x and y.

For example, the GCD of 8 and 12 is 4.

Is only defined on integer values.

Logaritm (base 10)

Bound to l. Calculates the 10-log of x.

Logaritm (Natural)

Bound to L. Calculates the natural logarithm of x.

Modulo

Bound to %. Calculates y mod x.

This also supports fractional modulo.

The sign of the result is the sign of x. So for example -1 mod 2 = 1, and 1 mod -2 = -1.

When used with the arrow, it calculates x mod arrow value.

Multiply

Bound to *. Calculates x*y.

If there is nothing in the stack, it will return a default value of 1.0.

Negative (additive inversion)

Bound to i (for invert). Calculates 0-x.

Invert (multiplicative)

Bound to I. Calculates 1/x.

Power of 10

Bound to e (e as used in scientific number notation). Calulates 10^x.

Power of e

Bound to E. Calulates e^x, where e is eulers constant (approx. 2.718).

Square

Bound to s. Calculates x*x.

Square root

Bound to S. Calculates sqrt(x).

Subtract

Bound to -. Calculates y-x.

Switch 2

Bound to tab. Swaps x and y.

If used with the arrow, switches the pointed at item with x.

Trigonomic functions

The most important trigonomic functions are also included. These all work based on radians, and are not currently settable to degrees.

Sin is bound to meta s.
Arcsin is bound to meta S.

Cos is bound to meta c.
Arccos is bound to meta C.

Tan is bound to meta t.
Arctan is bound to meta T.

Development Setup on Linux

Clone the repository into a directory.

git clone https://github.com/BartDeWaal/ERPN.git
cd ERPN

Create a virtual environment with pyvenv venv or (for python 3.6 and up) python3 -m venv venv.

Load it into your environment, the method depends on your shell. For bash it's source venv/bin/activate

Now install the package into the venv, using the "develop" command so you don't need to reinstall to apply changes

python setup.py develop

Now you can run it using the command erpn

Licence

GPLv3