Homework 8 Functional Visitors in DJ

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Homework 8 Functional Visitors in DJ
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• Use functional visitors to write a program that
  stores at each node in the abstract syntax tree
  the set of free variables.
• //Program.cd
• Program NodeList .
• Node lookahead (_at_ 2 _at_) AppNode LetNode
  lookahead (_at_ 2 _at_) AssignNode look ahead (_at_ 2 _at_)
  AddNode Term ProcNode .
• LetNode "let" Bindings "in" NodeList .
• AddNode ltagt Term "" ltbgt Term .
• Term VarNode LitNode .
• VarNode Ident .
• LitNode ltvgt int .
• ProcNode "proc" "(" FormalParameters ")"
  NodeList .
• AppNode Ident "(" ActualParameters ")" .
• AssignNode Ident "" Node .

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• Bindings List(Binding) .
• Binding Ident "" Node .
• FormalParameters NList(FormalParameter) .
• FormalParameter Ident .
• ActualParameters NList(ActualParameter) .
• ActualParameter Node .
• NodeList "begin" List(Statement) "end" .
• Statement Node "" .
• NList(S) S "," S .
• List(S) S .

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• begin //a
• let x 1 y 2 //a
• in
• begin
• proc(x,y) begin xy end
• let h3 //a, x, y
• in
• begin
• h a(x,y)
• end
• end
• ll 1
• end

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Functional Visitors

• Enable functional-style computation combinations,
  which are desirable for a lot of recursive
  computation scenarios.
• Object combine(Object values)specify the
  desired computation combination.
• Enable the flexibility of users to control the
  traversal according to the computation of Visitor
  itself.
• Object apply(String label)  go down to the edge
  labeled as label and return the value from the
  sub traversal

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LetNode
let h3 in begin
h a(x,y) end h, a, x, y
h a, x, y
bindings
nodelist
Bindings
NodeList

Binding
Ident
Node
FreeVariables(LetNode) (FreeVariables(NodeList)
Idents) FreeVariables(Nodes)

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Solution one

• /proj/demeter/com3362/w02/students/wupc
• 1 dehg fine around method to class LetNode,
  Ident,
• LitNode, Binding, ProcNode, FormalParameter .
• 2. Use List to store free variables, and HashMap
  to store bindings

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Solution two

• /proj/demeter/com3362/w02/students/lbenitez
• 1. Use a stack to store the nodes visited in the
  traversal, and a stack to store the bindings.
• 2. Define around method to class NodeList to
  compute free variables of the nodes in the node
  stack.
• 3. Define before and after methods to class
  LetNode, ProcNode to add a new binding field to
  the binding stack
• 4. Define before method to class Binding and
  FormalParameter to add a new binding to the
  current binding field
• 5. Define before method to subclasses of class
  Node to store the free variables of this node
  into the node stack.

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Solution three

• /proj/demeter/com3362/w02/students/qianyi
• 1 define around methods to node classes, same as
  the solution one. Some are not necessary.
• 2. Use HashSet store free variables and bindings

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Test example
begin let x 1 y 2 in
begin proc(x,y) begin xy
end let h3 in
begin h
a(x,y) end end
ll 1 end
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• LitNode_at_60d49()
• LitNode_at_5251a3()
• VarNode_at_75d386(x)
• VarNode_at_121f1d(y)
• AddNode_at_38e059(x,y,)
• NodeList_at_110040(x,y,)
• ProcNode_at_2786c3(x,y,)
• LitNode_at_88c0()
• VarNode_at_122221(x)
• VarNode_at_64f6cd(y)
• AppNode_at_2bb514(x,a,y,)
• AssignNode_at_7d5d2a(x,a,y,)
• NodeList_at_6fa474(x,a,y,)
• LetNode_at_15c083(x,a,y,) //2
• NodeList_at_11d8c1(x,a,y,)
• LetNode_at_2d9c06(a,) //1
• LitNode_at_7b6889()
• AssignNode_at_c2ff5()
• NodeList_at_39240e(a,)

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Caching aspect

• Parent
• Chind
• Caching
• Back
• MyCaching
• MyBack
• FreeVariableCaching

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Caching aspect

• pointcut caching(Parent c) call(void
  universal_trv0(..)) target(c) //??
• Question When we use a functional visitor in a
  traversal, which method is called of every node
  visited by this visitor.