Using variables

Text window or Edit window?

You can usually create variables in either conversational mode (in the text window) or in editing mode (in the edit window). In conversational mode, you need to make sure that you hit <enter> or <return> (whichever your system requires) at the end of a line for LOGO to take notice of that line. There is no feedback when using make. On the other hand, in editing mode, you can type a series of lines each followed by <return> and each perhaps creating some different variable. If at some point you then hit the key you use to escape from the editor, LOGO will try to interpret all of the lines you have typed and will then return you to the text window to continue normal conversation. It follows that if you just want to set up a variable or two, you would normally do this in conversational mode but if you are setting up a whole series of variables, then the editor is more appropriate.

Setting up and using variables

Create a number of different variables using make and then use them in conjunction with some of the primitive procedures you have learnt so far. E.g. type:

make "shopping [bread butter cheese milk]

and then use the variable in expressions with last, first, butfirst, fput etc. in various combinations. You could also try the primitive item.

If you need to review the use of these procedures click here.

Retrieving the value of a variable

Practice retrieving the value of a variable with thing or : (colon). Is thing an operation or a command?

Updating the value of a variable

Try using make to assign a new value to a variable you have previously created. Use thing to confirm that the value has been changed.

New variables from old

Create some new variables using existing variables. E.g. You have a list called "girls representing the girls in a family and another called "boys representing the boys. Create a new variable called "children using these two variables. What is the difference between using se versus list to do this. Can you imagine circumstances in which you would find one tactic more useful than the other?

4. Experiment with updating the value of one of your variables - i.e. modify it on the basis of its current value (rather than simply change it as in 2). E.g. if you have set up a variable called "shopping, see if you can change its value so that it no longer has the original first item on the list (as if you have just bought it) or change it by adding an item to the end of the original list (as if you have just remembered something).

What happens to :children (if you set it up as above above) when you subsequently update :boys.

Russian dolls

Try making some nested variables. E.g. make "doll1 "doll2 and so on. Now see if you can find out what is inside the innermost doll using thing ( and : to the extent that it is allowed).

Limits on names

How long can a variable name be in the system you are using? Are there any characters which are not accepted as part of a variable name (or for that matter as part of LOGO word)? Experiment to find out.

Keeping things tidy

For help on managing variables in your workspace, look here.



Ron Brasington
Department of Linguistic Science
The University of Reading
Reading
UK

E-mail: ron.brasington@rdg.ac.uk