Editing Diagrams/Dev/Constraints (section)

== What sorts of constraints are easy to support? ==
* linear? - supported in Z3, I implemented a few (alignAxis, spacingX/Y)
* linear inequalities? - they should be supported as well, but I haven't implemented anything that uses them.
* square / sqrt / distance? - also supported (less well), again I haven't done anything.
* sin / cos / angle? -- not supported in solvers ATM (although constant computations like sin pi work, thanks to sbv and my patches to it)
* constraints on Transformations? - I think you can write transformations with variables and then constrain the variables. So it should work already (Although I haven't actually tried it...)
* constraints on Measured Attributes? - Measured Attributes currently have a Data instance requirement. But CDouble can't do that, since it's a wrapper around IO, and all the functions in Data are pure. But CDouble's are actually more powerful than Measure (min/max/etc. are all first-class). So I think Measure and the Data constraint should just disappear (but that requires more diagrams-core changes)
* constraints on offsets / vectors in Paths? - I don't actually render Paths yet, due to the aforementioned Attribute problem.
* Which of the above are probably hard?
** Doing transcendental stuff like sin/cos constraints is hard, because (a) the mathematical solving is tricky and (b) you'd have to standardize it in SMTLIB somehow. But once it's implemented in your SMT solver of choice (Z3, YICES, etc.) then it's relatively easy to add to sbv, and then diagrams-constraints should just work (maybe after a few tweaks to the CDouble instances). Everything else is just coding. The diagrams-core rewrite is the hardest, and adding new primitives is the easiest.