Mjolner Tool Workshop

1.3 Exercise 3: Editing using syntactic code fragments

A central feature of the Mjolner tool is that it enables you to copy and move around large chunks of code quite easily -- without running into syntactic errors such as missing brackets etc. Unfortunately, it is difficult to illustrate the usefulness of this feature in a small example. Therefore this exercise consists of a description of the techniques required to use syntactic editing.

Load the file syntaxedit.bet.

1.3.1 Marking code fragments

First of all, you need to know how to mark a chunk of code. In the Mjolner tool it is impossible to mark something that is not a "whole", for instance you cannot select half a descriptor. The tool will always expand the marking until it fits a syntactic category.

In the example above, the selection becomes the entire pattern.

Another example: Mark from the middle of one pattern to the middle of the next.

The tool selects both patterns.

Try marking different chunks of code and observe what is being selected. For example, try marking the following:

UnregisteredVehicle: Vehicle ...;
Person: ... until aPerson: @person
Inside Person.print mark 'living at'->puttext
Inside Person.print mark the entire do-part

Experiment with the use of Alt+Up (overview), Alt+Left (abstract recursively), Alt+Right (detail) and Alt+Down (detail recursively).

1.3.2 Code fragments: Cut, copy & paste

The tool supports cut, copy, paste, undo and redo on the usual keys:

Command	Keyboard shortcut
cut copy paste undo redo	Ctrl+X Ctrl+C Ctrl+V Ctrl+Z Ctrl+Y

Now we want to move the Person pattern down to aPerson: @person:

Mark the Person pattern.
Press Ctrl+X to cut.
Mark Moped: UnregisteredVehicle.
Press Enter to insert code.
Press Ctrl+V to paste.

Now try undoing it all using Ctrl+Z.

Notice that the Person pattern could have been thousands of lines of code, and it would still be very simple to move it around or copy it.

You can apply this to all sorts of other code fragments: imperatives, descriptors, do-parts, enter-parts, exit-parts, variabels, superpattern-prefixes. But it does take a little practice to be able to use it efficiently.

Mjolner Tool Workshop

[Modified: Wednesday September 12^th 2001 at 17:10]