CSC302 2011S, Class 30: Interpreting Procedure Calls

Overview:
* A Bit About Procedures.
* Parameter Passing.
* An Operatational Approach.
* Jensen's Device.

Admin:
* Missing: AC, SA
* We'll use about fifteen minutes at the start of class to talk about 
  presentations.
* Readings for Monday (links on the Web)
  Graham, Paul (2002). Revenge of the Nerds.  
  Graham, Paul (2002). What Made Lisp Different.
* Post questions on Piazzza!
* EC for today's CS Table - Wolfram TED Talk [academic]
* EC for tonight's Bob's Benefit Bash [peer]

Presentations:
* ARS - (Aaron, Russel, Shitanshu)
  Potential Topic: CPS
* CAD - (Charles, Aditi, Dylan)
  Potential Topic: Software Transactional Memory (a model for concurrency)
* JAC - (Jeff, Andy, Chase)
  Potential Topic: GC
* Consanants (aka There weren't enough vowels to go around) 
  (Terian, Denny, Josh)
  Potential Topic: Programming languages for beginners (Alice, Scratch,
  Hypercard, Kodu) - a design issue; 
* Nyah (Jesse, David, Xin)
  Potential Topic: Monads and similar abstraction

The person who skipped class will decide what group it will join.

Dates:
* Fri week 12 (2011.04.29): JAC
* Mon week 13 (2011.05.02): CAD
* Wed week 13 (2011.05.04): ARS
* Fri week 13 (2011.05.06): Nyah
* Mon week 14 (2011.05.09): Consonants

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Procedures (aka Subroutines, Functions, Methods, Handlers)
* "Encapsulated and parameterized code"
* Four aspects that we normally look at
  * Signature / Declaration
    Gives name/parameters (types?)a
  * Definition / Implementation / Body
  * Call
  * Execution 
* Reminder: Use procedures for
  * Clarity
  * Concision
  * Checking
  * Calls, Recursive

Issue: Relationship between actual parameters (in the call) and formal
  parameters (in the definition)

Considerations:
* When do actuals get evaluated?
  * Eager: Before control is passed to the procedure
  * Lazy: Only when the "value" is used within the procedure
  * do_something_with (sqrt(sqrt(sqrt(4))))
  int do_something_with (x)
    return x + x/2 + x/4 + x/8 + x/16;
* Do we copy over the value of the actual or do we pass a reference/pointer
  to the actual?
* Do modifications to the formal affect the actual?

Calling Strategy	Value/Reference		Affect?		Eager/Lazy

Call-by-value		Value			No		Eager
Call-by-reference	Reference		Yes		Eager
Call-by-sharing		Value			Yes		Eager
Call-by-value-return	Value			yes		Eager
Call-by-text (macro)	???			yes (if variable) Lazy
Call-by-name (call-by-text with environment passing)