connection constraint

[ryo33]

[ryo33]

I think we don't need this in this crate because there is no universal constraint expression.

I have two ideas of expressions for constraint:

1. a list of all constraints
2. a function that returns a constraint for arguments

1. a list of all constraints

Pros

• nice data-driven API
• simple implementation

Cons

• explosion in numbers with many ports

2. a function that returns a constraint for arguments

Pros

• no explosion
• high dynamicity

Cons

• less data-driven