ConstraintParameter expression switches order when using an operation on a parameter

[MichaelAbdul-Masih]

When trying to create a constraint, it appears that the order of an expression in parentheses changes when a math operation is applied to the parameter. For example, the below behaves normally:

>>> (1 - b['ecc@binary'])
<ConstraintParameter: 1.000000 - {ecc@binary@component} (SI) => 1.0>

but when an operation is applied to the eccentricity parameter the expression order changes moving the parameter to the front and flipping the signs:

>>> (1 - b['ecc@binary']**2)
<ConstraintParameter: ({ecc@binary@component} ** 2.000000) - 1.000000 (SI) => -1.0>

The same happens when other operations are applied.

>>> from phoebe.parameters.constraint import sin
>>> (1 - sin(b['ecc@binary']))
<ConstraintParameter: (sin({ecc@binary@component})) - 1.000000 (SI) => -1.0>

The code can be tricked by explicitly putting the parameter first though. So the mathmatically equivalent espression below produces the correct result:

>>> (-1 * b['ecc@binary']**2 + 1)
<ConstraintParameter: (-1.000000 * ({ecc@binary@component} ** 2.000000)) + 1.000000 (SI) => 1.0>

[kecnry]

I'm not surprised that order matters (and you'll see lots of similar workarounds to what you showed in the built-in constraints themselves), but I think in the past this used to raise an error instead of giving the wrong expression - thanks for reporting this!