CS151, Class 9: User-Defined Procedures

Overview:
* Discussion of homework 1
* Why write procedures
* Writing your own procedures
* Lab
* Reflection: Interesting stuff you learned?

Notes:
* Homework 1 graded.  We'll spend some time looking at your work.
  + Education majors: Is evaluation or grading more important?
* Responses to surveys (finally) available online

Moral: Sam is a not-so-nice grader

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Useful to be able to encapsulate a common set of instructions

In most languages, we do this action with the procedure
* Key idea: A set of instuctions may be *parameterized*
  Meaning: You can write general instructions that take
   different inputs

In Scheme

(define _____
        NAME OF PROCEDURE
  (lambda (___ ___ ___ ___)
           PARAMS SEPARATED BY SPACES
     ____))
     EXP1
     

E.g.,

(define square
  (lambda (val)
    (* val val)))

Using it

> (square 4)
16

Basic model:
  Evaluate all the parameters and then plug them in in the
  expression.  Evaluate the expression.