Because it's inconsistent with expectations from mxAlgebra and elsewhere, it would be helpful when the typeCheck() hits a non-string argument for the error to say:
"Error in mxConstraint(): All three parameters need to be in quotes - parameter 1 (VP1) was not"
Comments
#1
Please see the forum post as to why this is an R issue, not an OpenMx issue. The same problem occurs in the following example that is not OpenMx related.
#2