[racket] Stepper and application in BSL

From: John Clements (clements at brinckerhoff.org)
Date: Sun Aug 29 22:38:41 EDT 2010

On Aug 29, 2010, at 7:11 PM, Justin Zamora wrote:

> I put the following in my definitions window (Beginning Student Language).
> (define (f x)
>  (+ x 1))
> (+ (f 3) 1)
> When I open the Stepper, (f 3) is highlighted in green, as expected.
> If I click "Step >", the expression changes to (+ (+ 3 1) 1), as
> expected (it stepped into the function).  However, if I instead click
> on "Application >", I get "All of the definitions have been
> successfully evaluated."  I expected to get (+ 4 1).  I thought the
> stepper would replace (f 3) with the result of the application.  Why
> didn't I see what I expected?

The "Application >" button jumps to the next step that reduces a function to its body.  That is, one whose "green" expression is a call to a non-primitive.

Frankly, it looks to me like the "Application >" button could be demoted to a menu entry in the "jump to..." choice box. 

John Clements

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