Module strength

Contains useful constants and functions for producing strengths for use in the constraint solver. Each constraint added to the solver has an associated strength specifying the precedence the solver should impose when choosing which constraints to enforce. It will try to enforce all constraints, but if that is impossible the lowest strength constraints are the first to be violated.

Strengths are simply real numbers. The strongest legal strength is 1,001,001,000.0. The weakest is 0.0. For convenience constants are declared for commonly used strengths. These are REQUIRED, STRONG, MEDIUM and WEAK. Feel free to multiply these by other values to get intermediate strengths. Note that the solver will clip given strengths to the legal range.

REQUIRED signifies a constraint that cannot be violated under any circumstance. Use this special strength sparingly, as the solver will fail completely if it find that not all of the REQUIRED constraints can be satisfied. The other strengths represent fallible constraints. These should be the most commonly used strenghts for use cases where violating a constraint is acceptable or even desired.

The solver will try to get as close to satisfying the constraints it violates as possible, strongest first. This behaviour can be used (for example) to provide a “default” value for a variable should no other stronger constraints be put upon it.

Constants

• MEDIUM
• REQUIRED
• STRONG
• WEAK

Functions

• clip
  Clips a strength value to the legal range
• create
  Create a constraint as a linear combination of STRONG, MEDIUM and WEAK strengths, corresponding to a b and c respectively. The result is further multiplied by w.