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Figure 4-18: This version of Square takes the desired color as a second parameter .

try it out 4-1
What about the thickness of the square’s border? Modify the Square procedure
to take a third parameter, called penSize, that specifies the size of the pen to be
used in drawing the square .

Let’s conclude this section with some useful tips for dealing with cus-
tom blocks:

• Custom blocks can’t be shared among sprites. If you create a cus-
tom block for, let’s say, Sprite1, then only Sprite1 can use that block.
Similarly, a custom block defined for the Stage can only be called by
scripts that belong to the Stage.
• Give your parameters meaningful names that indicate what they’re
used for.
• To delete a custom block, just drag its define block (that is, the hat
block) from the Scripts Area and drop it over the Palettes area. You
can only delete a define block if your project doesn’t contain any stack
blocks associated with it, so remove all uses of a custom block from your
scripts before trying to delete it.
• To delete a parameter of a custom block, click the parameter’s name
in the Edit Block dialog and then click the small X icon that appears
above the parameter’s slot.
• In addition to number inputs, you can also add string and Boolean
parameters. We’ll talk more about data types when we discuss variables
in the next chapter.

Now, you might wonder: Can a procedure call another procedure?
In the next section, you’ll learn about how to use nested procedure calls
to extend the power and usefulness of existing procedures.

Procedures 81

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