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## Buttons

The left end of the row of buttons in DrScheme contains a miniature button with the current file's name. Clicking the button shows the file's full pathname.

Below the filename button is a (define ...) button for a popup menu of names defined in the definitions window. Selecting an item from the menu moves the blinking caret to the corresponding definition.

The Save button appears whenever the definitions window is modified. Clicking the button saves the contents of the definitions window to a file. The current name of the file appears to the left of the Save button, but a file-selection dialog appears if the file has never been saved before.

The Step button starts The Foot, which shows the evaluation of a program as a series of small steps. Each evaluation step replaces an expression in the program with an equivalent one using the evaluation rules of DrScheme. For example, a step might replace `(+ 1 2)` with `3`. These are the same rules used by DrScheme to evaluate a program. Clicking Step opens a new window that contains the program from the definitions window, plus three new buttons: Next, Previous, and Home. Clicking Next performs a single evaluation step, clicking Previous retraces a single step, and clicking Home returns to the initial program. The Foot works only for programs using the Beginning Student language level.

The Check Syntax button checks the syntax of the program in the definitions window and colorizes keywords and primitive function names. It also enables pop-up arrows that show the relationship between variable declarations and their uses when the mouse cursor is moved over a variable. Modifying the program turns off the arrows until Check Syntax is clicked again.

The Execute button evaluates the program in the definitions window and resets the interactions window.

The Break button interrupts an evaluation, or beeps if DrScheme is not evaluating anything. For example, after clicking Execute or entering an expression into the interactions window, click Break to cancel the evaluation. Click the Break button once to try to interrupt the evaluation gracefully; click the button twice to killing the evaluation immediately.

An Analyze button appears if you have installed the MrSpidey static debugger. Clicking the button starts the debugger on the program. See PLT MrSpidey: Static Debugger Manual for more information.

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