expr-dice-roller 0.0.6

A dice roller expression language with function support.

Expression Dice Roller

Install from PyPI: pip install expr_dice_roller

Quick command-line dice roller set up:

from expr_dice_roller import evaluate
result = evaluate("3d20d1") # 3d20 and drop only the lowest roll.
print(result.value)

It is possible to serialize an expression by using format_expression(), which can then be used in evaluate().

It is also possible to serialize and deserialize an Environment.

Language Specifications

Arithmetic words with the operators +, -, *, /, and ^. Unary operators - and + are supported.

The language closely mirrors RPG Dice Roller's notations, with a few unimplemented or extra parts:

• Fudge dice is not yet implemented.
• Critical success / failures are not yet implemented.
• Grouping rolls are not yet implemented.
• New features includes variables and functions.

Variables

Variables have a name comprised of any string of characters that are not part of the language itself. There are no built-in variables except for the _ variable when evaluate() is called with assign_last_eval=True.

The _ variable, if provided, will point to the value of the last successful eval.

Functions

Functions are declared like so: f(x, y, z, ...) = expression. They can be immediately called if surrounded by brackets.

Example functions:

• f(x) = 2 * x - doubles the input.
• dice(count, sides) = (count)d(sides) - rolls count dice each with sides sides.
• dice(4, 3) - calls the dice function, effectively rolling a 4d3.
• (g(x, y)=f(x)-f(y))(2, 3) - immediately invoked function that calls another function.

Extraneous arguments beyond the arity of the function will be voided. Similarly, missing arguments below the arity of the function will be turned to 0.

Functions cannot be arbitrarily chained yet; currently, functions are parsed as special exceptions to certain rules.

Usage

Any ValueErrors when using evaluate() or format_expression() should be caught in the parent program.