Installation

pip install backward

Usage

>>> from backward import Backward

>>> ctx = Backward()
>>> _ = ctx.evaluate("a => b")
>>> _ = ctx.evaluate("b => c")
>>> _ = ctx.evaluate("= a")  # a is true
>>> ctx.evaluate("a b c")  # are b and c true?
[True, True, True]

You can also type python -m backward into your shell to enter an interactive REPL.

Syntax

C => E          # C implies E
A & B & C => D  # A and B and C implies D
A | B => C      # A or B implies C
A & !B => F     # A and not B implies F
C | !G => H     # C or not G implies H
V ^ W => X      # V xor W implies X
A & B => Y & Z  # A and B implies Y and Z

= A B G         # Initial facts : A, B and G are true. All others are false.
G V X           # What are G, V and X ?

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change. Please make sure to update tests as appropriate.