Commodore BASIC and Atari BASIC both had on screen editors where you could LIST your program on the screen and cursor up and down and change the code and when you pressed ENTER on a line, that line was re-entered into the program. Most other BASICs either required you to retype the entire line or had a line editor (eg. Applesoft BASIC).

Atari BASIC could export a BASIC program as a text file using the LIST command. Once exported, an editor could be used to edit the code:

  LIST "D1:CODE.TXT"

Or you could only output part of the program, say from line 1000 to 2000:

  LIST "D1:PARTIAL.TXT",1000,2000

Then you could use the ENTER command to bring that code back in. If a program was already there, the lines would simply be inserted. If the ENTERed code had a line number the same as the program in memory, it would replace the one already in memory. This was a great way to have a subroutine library, kind of like #include in C:

  ENTER "D1:PARTIAL.TXT"

Outside of the examples above, it was difficult to have a full screen editor for BASIC because every line had to have a line number and you had to keep them organized. Also, the earliest microcomputers didn't have enough RAM for a full screen editor. The BBC Micro had a text editor in ROM but it couldn't be used for BASIC code. It could be used for other languages that were typically compiled.

Most other languages either had a full screen editor or you could use any text editor. For example, Atari Logo has a full screen editor where you can edit one PROCEDURE at a time with:

  EDIT "MYPROCEDURE