Editing FOCAL (programming language) (section)

==Environment commands==
=== Running programs ===
FOCAL used {{code|GOTO}} in the editor to start a program. However, a rule-of-thumb was to shorten this to {{code|GO}}. This is the equivalent of {{code|RUN}} in BASIC. {{code|GOTO}} can also be used in the editor to start execution at a specified line.

=== Editing commands ===
New lines are entered into a program by simply starting the command with a line number. The editing commands were <code>ERASE</code> (abbreviation E),{{sfn|Manual|1968|p=2.4}} <code>MODIFY</code> (abbreviation M),{{sfn|Manual|1968|p=3.8}} and <code>WRITE</code> (abbreviation W):{{sfn|Manual|1968|p=3.2}}
* <code>ERASE</code> – zero out all variables; this is sometimes used in programs to reset them
* <code>ERASE ''line number''</code> – delete the statement at a specified line
* <code>ERASE ''group number''</code> – delete all statements in a specified group
* <code>ERASE ALL</code> – delete an entire program
* <code>MODIFY ''line number''</code> – allow editing a specified line
* <code>WRITE ''line number''</code> – display the statement at a specified line
* <code>WRITE ''group number''</code> – display all statements in a specified group
* <code>WRITE ALL</code> – display a specified program

=== File commands ===
The file command was OPEN (abbreviation O):
* {{code|OPEN INPUT [device:][file][,ECHO]}} – prepare to read from the start of a file
* {{code|OPEN OUTPUT [device:][file][,ECHO]}} – prepare to write from the start of a file
* {{code|OPEN RESTORE INPUT[,ECHO]}} – resume input
* {{code|OPEN RESTORE OUTPUT[,ECHO]}} – resume output
* {{code|OUTPUT CLOSE}} – output the buffer and close a file

=== Library commands ===
FOCAL included the ability to manage collections of FOCAL programs as a code library. Programs could call other programs in a chain fashion using <code>LIBRARY CALL</code>, or call a single subroutine in another program using <code>LIBRARY GOSUB</code>. Program names could be six characters long. The LIBRARY command (abbreviation L) had the following sub-commands:

* <code>LIBRARY DELETE [device:]''program name''</code> – delete a program
* <code>LIBRARY LIST [device:][file name]</code> – catalog
* <code>LIBRARY RUN [device:]''program name'' [line number]</code> – chain a program, optionally resuming at a specified line number
* <code>LIBRARY SAVE [device:]''program name''</code> – save a program
* <code>LIBRARY EXIT</code> – return to the PDP-8 monitor program
FOCAL-71 added:
* <code>LIBRARY CALL [device:]''program name''</code> – load a program
* <code>LIBRARY GOSUB [device:]''program name'' [group number]</code> – call a subroutine in an external program