error messages to specify missing variable

[Stuart]

Error messages like this

error no.4:No such variable on line 892 (reported by my error handler)

are helpful, but it would be even more helpful if they could have access to the name of the missing variable, which I assume has to be known. Especially as sometimes it does not seem to be a valid complaint.

[cicciocb]

Yes I understand the point and I'll try to implement this.
Eventually I could just return the position, on the line, where the error is detected (i.e. No such variable on line 892:22 for an error at the position 22)