Com S 641 meeting -*- Outline -*-

* Variables (2.9-10)

** declarations (2.9)

	Q: How is alias abstraction different from a variable
		declaration in a language like C or C++?
	A var decl allocates new storage, and also binds id to it.
		may also allow initialization

	Q: What kind of evaluation is used for variable declarations?
		eager: allocation and initialization
			happens right away

	so a var decl is part declaration (the binding)
		and part command (the allocation)

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      VARIABLE DECLARATIONS (2.9)

Abstract Syntax:

  D ::= var I | ...
  C ::= L := E | ...
  E ::= @L | ...
  L ::= I


Examples:





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	Note that the variable names

	var x, var y, var temp;
        proc swap = (temp := @x; x := @y; y := @temp)
        in x := 5; y := 4; call swap

	Q: Does the copy rule work for programs like this?

** semantics (2.10)
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    SEMANTICS OF VAR DECLARATIONS (2.10)

[[pi |- var I:

where 
and allocate : Store -> (Location x Store)
    allocate [n1,...,nk] = 

    where init is some arbitrary Integer






         
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	... {I:intloc}dec]] e s = ({I=l}, s')
	... (l,s') = allocate(s)

	Q: How does this change the type of the semantic equations
		for declarations?
	now takes a store,
		and returns a pair of environment and store.

	Q: Do we have to make changes to the other
		kinds of declarations?
	   yes, need to have them return store also
		(or use a monad...)

	... [[pi |- define I=U:	{I:theta}dec]]e s = ({I = f}, s),
		where f s' = [[pi |- U:theta]]e s'

	Q: any other changes?
		need to change the semantics of programs (D in C)
                        to extract the final store from the declaration (D)

	... [[D in C: comm]]s = [[pi |- C: comm]]e1 s1,
		where (e1,s1) = [[ emptyset |- D: pi dec]]\emptyset s