Editing Procedures

Entering procedures directly is fine for very simple procedures, but for anything more complex it is likely that some mistakes will be made in entering the procedures. When this happens it will be necessary to edit the procedure. Editing is accomplished from within ICL using standard editors. For example the command

    ICL> EDIT SQUARE_ROOT

would be used to edit the SQUARE_ROOT procedure. By default the TPU editor is used. It is also possible to select the EDT or LSE editors using the SET EDITOR command. All these editors are described in DEC's documentation.

When editing a procedure there are two possible options.

• We can leave the name of the procedure unchanged, but edit the code. In this case we create a new version of the procedure, which replaces the old one when we exit from the editing session.
• We can change the name of the procedure by editing the PROC statement at the start of the procedure. This creates a new procedure with the new name, and leaves the old procedure unchanged.

It is possible to enter procedures completely using the editors. However it is recommended that procedures be entered originally using direct entry. The advantage is that during direct entry, any errors will be detected immediately. Thus if we mistype the PRINT line in the above example we get the following error message:

    SQUARE_ROOT> PRINT The Square Root of (X is (SQRT(X))
    PRINT The Square Root of (X is (SQRT(X))
                                ^
    Right parenthesis expected

The error message consists of the line in which the error was detected. A pointer which indicates where in the line ICL had got to when it found something was wrong, and a message indicating what was wrong. In this case it found the 'is' string when a right parenthesis was expected.

Following such an error message we can use the command line editing facility to correct the line and reenter it. If the same error occurred during procedure entry using an editor, the error message would only be generated at the time of exit from the editing session, and it would be necessary to EDIT the procedure again to correct it.