Creating Instances of Student-Defined Structures

If you are going to require students to use a particular structure (for example, to represent nodes of a tree), the ideal is to place the structure definition in a module, provide the necessary creation, accessor, and if necessary mutator functions, and then either have students (require ...) it or import it as a teachpack. You can then supply this module as part of the testing suite, and add an extra function that returns particular pre-defined testing values. The reason to want pre-defined values is if the structures are complex, and you will want to use a given one for more than one test.

If this is not done in a teachpack, your module has no direct way of seeing the student-defined structure's creation function. The way around this is to provide an appropriate macro (instead of a function, so that it's usable in a Beginning Student context) from one of your testing modules.

As an example for a tree:

#lang scheme                                                                                                                                                            
(provide get-tree)
                                                                                                           
(define-syntax get-tree
  (syntax-rules (small medium)
    ((_ small mknode)
     (mknode 1 'apple empty empty))
    ((_ medium mknode)
     (mknode 1 'banana
             (mknode 2 'orange empty empty)
             (mknode 3 'pineapple
                     (mknode 4 'mango empty empty)
                     empty)))))

Then, you can grab one of these trees with an expression such as

(get-tree medium make-node)

Note that this still requires the students to name their structure very precisely; otherwise, the testing suite still will not be able to find it.

See also: SchemeModuleCompareUnknownStructs.