CoCoA » CoCoA-5

I have set the target version as 5.3.4, but this may be wildly optimistic.
I fear that this request may be rather hard, or even impossible (without making BuiltinOneLiners much more complicated).

Here is an example of what I mean:

/**/ pi := 3.14159;
/**/ CFApprox(pi,2);
--> ERROR: Expecting type RAT, but found type INT
--> CFApprox(pi,2);
-->             ^
/**/ CFApprox(pi,3/2);
--> ERROR: The arg(s) given are unsuitable
--> [CoCoALib] CFApprox: relative error must be between 0 and 1
--> CFApprox(pi,3/2);
--> ^^^^^^^^^^^^^^^^

The 2nd arg must be a rational between 0 and 1. In the first case the troublesome arg is identified; in the second just the whole call is highlighted.

I believe that the error must be clear enough in CoCoALib so that there is no need to intercept (all??) situations like this.