Store global variables in a const structure

[dpsanders]

Using global variables as in

ProbabilityBoundsAnalysis.jl/src/ProbabilityBoundsAnalysis.jl

Line 70 in 652700c

global steps = 200 # discretization levels of probability

is a performance trap.

To fix this, I suggest grouping all the global variables into a mutable struct, which you refer to via a const global. See e.g.

https://github.com/JuliaIntervals/IntervalArithmetic.jl/blob/db9202ccd08402d05616442f395e88cb21f79b9b/src/intervals/precision.jl

for a similar design.

[dpsanders]

Part of the review for the JuliaCon proceedings: JuliaCon/proceedings-review#96

[AnderGray]

Thank you for this suggestion. I have followed the example from IntervalArithmetic.jl. In future it would be good to also remove these globals