Parsing variables

[smkatz12]

Solve this (per discussion earlier):

upright = s -> abs(s[1]) < π / 4
ψ = @formula □(upright)

[mossr]

Variables now work. Due to some idiosyncrasies with Julia's metaprogramming, you first have to define the upright function as a @formula then you can use it in combination with @eval and interpolation with $

upright = @formula s -> abs(s[1]) < π / 4
ψ = @eval @formula □($upright)

Also note that if you want to use variable thresholds, you have to do the same thing:

λ = 0.5
ψ = @eval @formula s->s > $λ

This is a limitation of Julia's metaprogramming.