It could be considered a non-lie under the concept of mental reservation. In older usage, coding a computer meant writing assembly or machine language only; thus, a report on FORTRAN indicates that "FORTRAN virtually eliminates coding and debugging". This is a standard usage of the word coding although slightly archaic.

http://www.softwarepreservation.org/projects/FORTRAN/BackusE...

Otherwise, presenting informal proofs to students in engineering or science that would not be considered mathematically rigorous would also be a lie and unethical.