While reading or editing a program, the Elan Programming Environment accepts text from a file or from the keyboard, one definition at a time, and translates it to internal form, performing a running Context-Free syntax check as the lines come in.
Upon finding a syntactic error, the translator attempts to arrive at a syntactically correct program in interaction with the user, offering the incorrect definition for local editing as often as necessary. By hitting <BREAK> the user may end this attempt.
The editing of existing parts of a program is based on replay: some definition is displayed on the screen, and can be modified at will by the user, after which the translator reads the text on the screen as input. The new definition may overwrite the old one.