Function template for compound output types

Suppose the data definition for the output reveals that the output is of a compound data type, e.g.

    ; Data definition: 

    ; A student is a symbol (name), an integer (ID), and a number (GPA) 

    (define-struct student (name ID GPA))

I recommend that after writing a define-struct, you immediately write down the contracts for all the functions that it defines for you, so the above example becomes

    ; Data definition:
    ; A student is a symbol (name), an integer (ID), and a number (GPA)
    (define-struct student (name ID GPA))
    ; make-student: symbol, integer, number => student
    ; student-name: student => symbol
    ; student-ID: student => integer
    ; student-GPA: student => number
    ; student?: object => boolean

In particular, since your function has to return a student, it's likely to use the make-student function:

  (define (func-returning-student ...)
     (make-student symbol integer number))

in which each of the slots symbol, integer, and number needs to be filled in with something of the appropriate type. Each of these may be a constant, an argument from the function header, or a complex expression in its own right, but it must be of the right type.

Last modified: Thu Jan 20 10:36:51 EST 2000

Stephen Bloch / sbloch@adelphi.edu