[FR] Proposition Uniqueness

[haz]

Willingness to contribute

The Bauhaus Community encourages new feature contributions. Would you be willing to contribute an implementation of this feature?

• Yes. I can contribute this feature independently.
• Yes. I would be willing to contribute this feature with guidance from the Bauhaus community.
• No. I cannot contribute this feature at this time.

Proposal Summary

Proposition objects are created as unique, and so if you create multiple copies for various constraints, then it can lead to unintuitive bugs. By default, we should have a proposition be uniquely identified by it's representation (or a hash of that), and then we can create the object repeatedly and refer to the same proposition in the code.

Motivation

Is your feature request related to a problem? Please describe.

This shows what currently doesn't work, but should:

from bauhaus import Encoding, proposition, constraint

e = Encoding()

@proposition(e)
class V(object):
    pass

# Works: x refers to the same proposition
x = V('x')
y = V('y')
z = V('z')
E.add_constraint(x | y)
E.add_constraint(x | z)

# Doesn't work: each x is a unique proposition
E.add_constraint(V('x') | V('y'))
E.add_constraint(V('x') | V('y'))

While it doesn't seem like that much of a difference here, it can be largely problematic for large encodings with several variables.

Describe the solution you'd like

• Force implementers to define the method _prop_name on their objects using @proposition. If it's not there, throw an error.
• Return the outcome of this method for __repr__.
• Overload __hash__ and __eq__ appropriately (e.g., [this hack]).

Why is it currently difficult to achieve this with Bauhaus?
It's not implemented.