Safe evaluation

[blegat]

The number 1 issue with DP is with the following:

@polyvar x y
p = x + y
p(x => 1) # Garbage

What prevents us from showing a nice error message is that checking whether all variables are assigned would make the evaluation slower. We could maybe replace https://github.com/JuliaAlgebra/MultivariatePolynomials.jl/blob/cd76ab85ef40d2b4d3bce2f1330e56ef5142d1b6/src/substitution.jl#L21 by

struct Eval <: AbstractSubstitutionType
    check::Bool
end

and if check is true (which would be the default), the call will need to take an extra time if needed to make a nice error messages in case not all variables are assigned a value.

What do you think ?

cc @chriscoey

[saschatimme]

Doesn't this check only has to be done once at the beginning? I would be completely fine with this, since I only use DynamicPolynomials for construction of systems and lightweight analysis, so no evaluation heavy stuff. Also I think it would be better to be by default on the safe side, since the current behaviour is very subtle and even can happen unnoticed.

[blegat]

What do you mean at the beginning ? I imagine doing the check here: https://github.com/JuliaAlgebra/DynamicPolynomials.jl/blob/a546440ea886873e6b3ccf073984465c62f30e3d/src/subs.jl#L30 with a BitSet instead of https://github.com/JuliaAlgebra/DynamicPolynomials.jl/blob/a546440ea886873e6b3ccf073984465c62f30e3d/src/subs.jl#L33-L35 which doesn't work for Int, ...

[chriscoey]

I agree with defaulting to the safe side (I had some headaches caused by silent garbage).

How would the user set check?

[blegat]

How would the user set check?

MP.subs(MP.Eval(false), p, x => 1)