CS302 2007S, Class 08: Higher-Order Graphics

Admin:
* I got the talks wrong 
  Tomorrow's talk is on the Automation of Athletic Recruiting.
* Are there questions on HW3?
* Friday's reading is also online (Representing Images).
* Three readings distributed for next Monday.  
  * "What Made Lisp Different" subsetof "Revenge of the Nerds"
  * Comment on both.  (For RotN, comment on something other than WMLD)
* Slight rearrangement of syllabus

Overview:
* Thinking functionally.
* The basics of higher-order procedures.
* Lab.

/What is Functional Programming?/

* Not as linear as procedural programming
  * We don't have to follow a sequence of operations
  * (proc param0 param1 param2 ... paramn)
  * A procedural programmer would be likely to do a sequence of
    function calls
    * A real functional programmer would simply nest
* Functions are "first class" values
  * They can be parameters to other procedures
  * They can be returned from other procedures
  * They can be created "dynamically"
* Scheme is more "mathematical" - "pure"
  * In C and Java, the model is that function calls have side
    effects (and are done for the side effects)
  * In a well-designed functional language, a well-designed
    procedure is called only for its return value
    * Answers are reproducible
    * Analysis is easier

/START OF DETOUR ON PURITY/
a = 10;
foo();
print(a);

public class Variable
{
  int contents;
  public void set(int newval)
  {
    this.contents = newval;
  }
  public int get()
  {
    return this.contents;
  }
  public String toString()
  {
    return Integer.toString(this.contents);
  }
}
public void silly(Variable a, Variable b)
{
  a.set(10);
  b.set(20);
  out.println(a);
}

/END OF DETOUR ON PURITY/

* Built-in symbol type
  * Faster comparison
  (define what-should-i-do
    (lambda (day)
      (if (member day (list 'sunday 'tuesday 'thursday))
          "Send Sam a reflection on the reading NOW"
	  "Do the reading, so you can send sam a reflection")))

in C
typdef days enum (monday, tuesday, wednesday, thursday, friday, saturday, sunday);
switch (day) {
  case sunday: case tuesday: case thursday: return "Send reflection"; break;
  case default: return "Read"; break;
}
* Garbage collection
* Code and data are "indistinguishable"
  * You can execute data
  * You can treat code as data

/HOP - A Key Functional Concept/

/Lab/