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Walker Class Reference
[AST Traversal functional classes.]

A functional class to traverse an AST, and perform some function at each of its Nodes. More...

#include <walker.h>

Inheritance diagram for Walker:

callGraph df_number_walker enum_value_walker fix_goto_walker gcWalker goto_label_walker has_struct_walker init_flowproblem_walker Linker LivenessComments LivenessWalker print_walker procedureDB ProcWalker reachingDefinitionsWalker ref_fix_walker scope_walker semcheck_walker set_container_walker sue_complete_walker TreeChecker UnificationBasedPtr UnitWalker vcgWalker List of all members.

Public Types

enum  Order { Preorder, Postorder, Both }
 The order in which AST Nodes should be visited. More...
enum  Depth { Subtree, NodeOnly }
 Which Nodes in the AST tree should be visited. More...

Public Member Functions

 Walker (Order the_order, Depth depth)
 Create a new instance of a Walker.
Accessors
Methods to get and set fields in the class.

Order order () const
 Return the order in which Nodes of an AST should be visited.
Depth depth () const
 Return which Nodes of an AST should be visited.
"at_" methods
These methods define the functions that should be performed when different classes of Nodes are encountered in the AST. The most specific "at_" method that matches a given Node's class will be called.

virtual void at_node (Node *the_node, Order ord)
virtual void at_unit (unitNode *the_unit, Order ord)
virtual void at_def (defNode *the_def, Order ord)
virtual void at_decl (declNode *the_decl, Order ord)
virtual void at_subdecl (subdeclNode *the_subdecl, Order ord)
virtual void at_proc (procNode *the_proc, Order ord)
virtual void at_type (typeNode *the_type, Order ord)
virtual void at_prim (primNode *the_prim, Order ord)
virtual void at_tdef (tdefNode *the_tdef, Order ord)
virtual void at_ptr (ptrNode *the_ptr, Order ord)
virtual void at_array (arrayNode *the_array, Order ord)
virtual void at_func (funcNode *the_func, Order ord)
virtual void at_sue (sueNode *the_sue, Order ord)
virtual void at_struct (structNode *the_struct, Order ord)
virtual void at_union (unionNode *the_union, Order ord)
virtual void at_enum (enumNode *the_enum, Order ord)
virtual void at_suespec (suespecNode *the_suespec, Order ord)
virtual void at_expr (exprNode *the_expr, Order ord)
virtual void at_index (indexNode *the_index, Order ord)
virtual void at_const (constNode *the_const, Order ord)
virtual void at_id (idNode *the_id, Order ord)
virtual void at_binary (binaryNode *the_binary, Order ord)
virtual void at_unary (unaryNode *the_unary, Order ord)
virtual void at_cast (castNode *the_cast, Order ord)
virtual void at_comma (commaNode *the_comma, Order ord)
virtual void at_ternary (ternaryNode *the_ternary, Order ord)
virtual void at_call (callNode *the_call, Order ord)
virtual void at_initializer (initializerNode *the_initializer, Order ord)
virtual void at_stmt (stmtNode *the_stmt, Order ord)
virtual void at_block (blockNode *the_block, Order ord)
virtual void at_basicblock (basicblockNode *the_basicblock, Order ord)
virtual void at_exprstmt (exprstmtNode *the_exprstmt, Order ord)
virtual void at_target (targetNode *the_target, Order ord)
virtual void at_label (labelNode *the_label, Order ord)
virtual void at_case (caseNode *the_case, Order ord)
virtual void at_selection (selectionNode *the_selection, Order ord)
virtual void at_if (ifNode *the_if, Order ord)
virtual void at_switch (switchNode *the_switch, Order ord)
virtual void at_loop (loopNode *the_loop, Order ord)
virtual void at_while (whileNode *the_while, Order ord)
virtual void at_do (doNode *the_do, Order ord)
virtual void at_for (forNode *the_for, Order ord)
virtual void at_jump (jumpNode *the_jump, Order ord)
virtual void at_goto (gotoNode *the_goto, Order ord)
virtual void at_continue (continueNode *the_continue, Order ord)
virtual void at_break (breakNode *the_break, Order ord)
virtual void at_return (returnNode *the_return, Order ord)
virtual void at_attrib (attribNode *the_attrib, Order ord)
virtual void at_operand (operandNode *the_oper, Order ord)
virtual void at_conditiongoto (conditiongotoNode *the_condgoto, Order ord)
virtual void at_threeAddr (threeAddrNode *the_3addr, Order ord)
virtual void at_text (textNode *the_text, Order ord)

Private Attributes

Order _order
 The order in which AST Nodes should be visited.
Depth _depth
 Which Nodes in the AST should be visited.

Detailed Description

A functional class to traverse an AST, and perform some function at each of its Nodes.

A Walker is a functional class that traverses an abstract syntax tree, and performs some function at each of its Nodes. At each Node, the function it performs depends on the class of the Node.

Corresponding to each class in the Node hierarchy, Walker defines an "at_" method. To specify the function that should be performed for Nodes of a particular class, create a subclass of Walker that overrides the "at_" method corresponding to that class. By default, the "at_" methods perform no action. Thus, a Walker subclass only needs to override the "at_" methods corresponding to Node types that are relevant to that walker.

As the AST is traversed, the most specific "at_" method that has been defined for each Node will be called on that Node. For example, if a Walker subclass overrides "at_decl()", but not "at_subdecl()," then the "at_decl()" method wil be called for all declNodes and subDeclnodes encountered in the AST. However, if a Walker subclass overrides both "at_decl()" and "at_subdecl," then the "at_decl()" method will be called for all declNodes encountered in the AST, and the "at_subdecl()" method will be called for all subdeclNodes encountered in the AST. If you wish for both "at_subdecl()" and "at_decl()" to be called for subdeclNodes, then you should explicitly call the "at_decl()" method from "at_subdecl()."

As the walker traverses the AST, the "at_" methods for a Node can be called before its children have been visited, after its children have been visited, or both before and after its children have been visited. When the "at_" methods for a Node are called before its children, they are said to be called in "preorder." When the "at_" methods for a Node are called after its children, they are said to be called in "postorder." If "at_" methods are called both in preorder and in postorder, then the preorder call will always preceed the postorder call.

When a new Walker is created, the order(s) that Nodes are visited in should be specified. In general, all instances of a given subclass of Walker will visit Nodes in the same order. However, it may occasionally be useful to specify different orders for two different instances of the same subclass of Walker.

New instances of Walker can also specify the "depth" of the traversal. If the depth is "SubTree," then a Walker will visit the entire AST rooted at the Node that it is called on. If the depth is "NodeOnly," then the Walker will only call the "at_" method for Node it is called on, and not for any of its sub-Nodes. Thus, a Walker with a depth of NodeOnly functions as if it were a Visitor. If a Walker subclass will always use a depth of NodeOnly, then it should be written as a Visitor instead. The depth value is provided because it can occasionally be useful to use a Walker subclass that was designed to traverse an entire AST to simply visit one Node. In this case, you can simply instantiate the Walker subclass with a depth of NodeOnly.

It is possible for a Walker to modify the fields of the Nodes it visits. However, Walkers should not modify the structure of the AST that is being traversed. In other words, Walkers should only modify Node fields that do not contain sub-Nodes. If the structure of the traversed AST needs to be modified as it is traversed, then a Changer should be used instead of a Walker.

Currently, Walkers traverse the AST in a depth-first order. Preorder calls to the "at_" methods are called before descending into a Node's children, and postorder calls to the "at_" method are called after returning from the children in the traversal. At the leaves, the postorder calls to the "at_" methods immediately follow the preorder calls. However, this ordering is subject to change, and should not be relied upon. The only aspects of the AST traversal ordering which are guaranteed are:

  • The preorder call to a Node's "at_" method is called before any of the calls to the "at_" methods of the Node's descendants.
  • The postorder call to a Node's "at_" method is called after any of the calls to the "at_" methods of the Node's descendants.
  • The preorder call to a Node's "at_" method is called before the postorder call to a Node's "at_" method is called.

Walkers should never be used to traverse ASTs containing cycles; since they detect no mechanism to detect cycles, this would cause an infinite loop.

To use a walker "my_walker" to traverse an AST rooted at "my_node," use the code:

  my_node->walk(my_walker);

See also:
Visitor

Changer

Node::walk

Definition at line 142 of file walker.h.


Member Enumeration Documentation

enum Walker::Depth
 

Which Nodes in the AST tree should be visited.

Enumeration values:
Subtree  The entire AST should be traversed.
NodeOnly  Only the root Node should be visited.

Definition at line 155 of file walker.h.

enum Walker::Order
 

The order in which AST Nodes should be visited.

Enumeration values:
Preorder  Nodes should be visited before their children.
Postorder  Nodes should be visited after their children.
Both  Nodes should be visited both before and after their children.

Definition at line 147 of file walker.h.


Constructor & Destructor Documentation

Walker::Walker Order  the_order,
Depth  depth
[inline]
 

Create a new instance of a Walker.

This constructor is usually called by a subclass.

Parameters:
the_order The order in which AST Nodes should be visited. Nodes can be visited before their children (Preorder), after their children (Postorder), or both (Both).
depth Specifies which Nodes in the AST should be visited. A value of SubTree specifies that the entire AST should be traversed. A value of NodeOnly specifies that only the root Node in the AST should be visited. In general, this parameter should never be hard-coded as NodeOnly; instead, a Visitor should be used. However, the constructor for a subclass of Walker may take a Depth as one of its arguments, and pass it to the Walker subclass.

Definition at line 187 of file walker.h.


Member Function Documentation

virtual void Walker::at_array arrayNode the_array,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 254 of file walker.h.

References at_type().

virtual void Walker::at_attrib attribNode the_attrib,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker.

Definition at line 365 of file walker.h.

References at_stmt().

virtual void Walker::at_basicblock basicblockNode the_basicblock,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker, LivenessWalker, LivenessComments, and reachingDefinitionsWalker.

Definition at line 314 of file walker.h.

References at_block().

virtual void Walker::at_binary binaryNode the_binary,
Order  ord
[inline, virtual]
 

Reimplemented in gcWalker, id_lookup_walker, TreeChecker, and print_walker.

Definition at line 287 of file walker.h.

References at_expr().

virtual void Walker::at_block blockNode the_block,
Order  ord
[inline, virtual]
 

Reimplemented in scope_walker, and print_walker.

Definition at line 311 of file walker.h.

References at_stmt().

Referenced by at_basicblock().

virtual void Walker::at_break breakNode the_break,
Order  ord
[inline, virtual]
 

Reimplemented in ref_fix_walker, set_container_walker, TreeChecker, and print_walker.

Definition at line 359 of file walker.h.

References at_jump().

virtual void Walker::at_call callNode the_call,
Order  ord
[inline, virtual]
 

Reimplemented in id_lookup_walker, Linker, ref_fix_walker, TreeChecker, and print_walker.

Definition at line 302 of file walker.h.

References at_expr().

virtual void Walker::at_case caseNode the_case,
Order  ord
[inline, virtual]
 

Reimplemented in ref_fix_walker, semcheck_walker, set_container_walker, TreeChecker, and print_walker.

Definition at line 326 of file walker.h.

References at_target().

virtual void Walker::at_cast castNode the_cast,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 293 of file walker.h.

References at_expr().

virtual void Walker::at_comma commaNode the_comma,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 296 of file walker.h.

References at_expr().

virtual void Walker::at_conditiongoto conditiongotoNode the_condgoto,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, print_walker, LivenessWalker, and LivenessComments.

Definition at line 371 of file walker.h.

References at_goto().

virtual void Walker::at_const constNode the_const,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 281 of file walker.h.

References at_index().

virtual void Walker::at_continue continueNode the_continue,
Order  ord
[inline, virtual]
 

Reimplemented in ref_fix_walker, set_container_walker, TreeChecker, and print_walker.

Definition at line 356 of file walker.h.

References at_jump().

virtual void Walker::at_decl declNode the_decl,
Order  ord
[inline, virtual]
 

Reimplemented in id_lookup_walker, name_mangle_walker, semcheck_walker, TreeChecker, ProcWalker, print_walker, has_struct_walker, and UnificationBasedPtr.

Definition at line 233 of file walker.h.

References at_def().

Referenced by at_subdecl().

virtual void Walker::at_def defNode the_def,
Order  ord
[inline, virtual]
 

Definition at line 230 of file walker.h.

References at_node().

Referenced by at_decl(), and at_proc().

virtual void Walker::at_do doNode the_do,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker.

Definition at line 344 of file walker.h.

References at_loop().

virtual void Walker::at_enum enumNode the_enum,
Order  ord
[inline, virtual]
 

Reimplemented in enum_value_walker, and id_lookup_walker.

Definition at line 269 of file walker.h.

References at_sue().

virtual void Walker::at_expr exprNode the_expr,
Order  ord
[inline, virtual]
 

Definition at line 275 of file walker.h.

References at_node().

Referenced by at_binary(), at_call(), at_cast(), at_comma(), at_index(), at_initializer(), at_operand(), at_ternary(), and at_unary().

virtual void Walker::at_exprstmt exprstmtNode the_exprstmt,
Order  ord
[inline, virtual]
 

Reimplemented in semcheck_walker, and print_walker.

Definition at line 317 of file walker.h.

References at_stmt().

virtual void Walker::at_for forNode the_for,
Order  ord
[inline, virtual]
 

Reimplemented in semcheck_walker, TreeChecker, and print_walker.

Definition at line 347 of file walker.h.

References at_loop().

virtual void Walker::at_func funcNode the_func,
Order  ord
[inline, virtual]
 

Reimplemented in scope_walker, TreeChecker, print_walker, and has_struct_walker.

Definition at line 257 of file walker.h.

References at_type().

virtual void Walker::at_goto gotoNode the_goto,
Order  ord
[inline, virtual]
 

Reimplemented in goto_label_walker, fix_goto_walker, ref_fix_walker, TreeChecker, ProcWalker, and print_walker.

Definition at line 353 of file walker.h.

References at_jump().

Referenced by at_conditiongoto().

virtual void Walker::at_id idNode the_id,
Order  ord
[inline, virtual]
 

Reimplemented in callGraph, id_lookup_walker, Linker, name_mangle_walker, ref_fix_walker, TreeChecker, and print_walker.

Definition at line 284 of file walker.h.

References at_index().

virtual void Walker::at_if ifNode the_if,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 332 of file walker.h.

References at_selection().

virtual void Walker::at_index indexNode the_index,
Order  ord
[inline, virtual]
 

Definition at line 278 of file walker.h.

References at_expr().

Referenced by at_const(), and at_id().

virtual void Walker::at_initializer initializerNode the_initializer,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 305 of file walker.h.

References at_expr().

virtual void Walker::at_jump jumpNode the_jump,
Order  ord
[inline, virtual]
 

Definition at line 350 of file walker.h.

References at_stmt().

Referenced by at_break(), at_continue(), at_goto(), and at_return().

virtual void Walker::at_label labelNode the_label,
Order  ord
[inline, virtual]
 

Reimplemented in goto_label_walker, name_mangle_walker, TreeChecker, ProcWalker, and print_walker.

Definition at line 323 of file walker.h.

References at_target().

virtual void Walker::at_loop loopNode the_loop,
Order  ord
[inline, virtual]
 

Reimplemented in semcheck_walker, set_container_walker, TreeChecker, and init_flowproblem_walker.

Definition at line 338 of file walker.h.

References at_stmt().

Referenced by at_do(), at_for(), and at_while().

virtual void Walker::at_node Node the_node,
Order  ord
[inline, virtual]
 

Reimplemented in gcWalker, goto_label_walker, set_container_walker, sue_complete_walker, TreeChecker, and df_number_walker.

Definition at line 223 of file walker.h.

Referenced by at_def(), at_expr(), at_stmt(), at_text(), at_type(), and at_unit().

virtual void Walker::at_operand operandNode the_oper,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 368 of file walker.h.

References at_expr().

virtual void Walker::at_prim primNode the_prim,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker.

Definition at line 245 of file walker.h.

References at_type().

virtual void Walker::at_proc procNode the_proc,
Order  ord
[inline, virtual]
 

Reimplemented in vcgWalker, id_lookup_walker, name_mangle_walker, ref_fix_walker, scope_walker, set_container_walker, TreeChecker, UnitWalker, print_walker, init_flowproblem_walker, LivenessWalker, LivenessComments, reachingDefinitionsWalker, and UnificationBasedPtr.

Definition at line 239 of file walker.h.

References at_def().

virtual void Walker::at_ptr ptrNode the_ptr,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker.

Definition at line 251 of file walker.h.

References at_type().

virtual void Walker::at_return returnNode the_return,
Order  ord
[inline, virtual]
 

Reimplemented in ref_fix_walker, semcheck_walker, set_container_walker, TreeChecker, print_walker, LivenessWalker, and LivenessComments.

Definition at line 362 of file walker.h.

References at_jump().

virtual void Walker::at_selection selectionNode the_selection,
Order  ord
[inline, virtual]
 

Reimplemented in semcheck_walker.

Definition at line 329 of file walker.h.

References at_stmt().

Referenced by at_if(), and at_switch().

virtual void Walker::at_stmt stmtNode the_stmt,
Order  ord
[inline, virtual]
 

Reimplemented in init_flowproblem_walker, and LivenessWalker.

Definition at line 308 of file walker.h.

References at_node().

Referenced by at_attrib(), at_block(), at_exprstmt(), at_jump(), at_loop(), at_selection(), at_target(), and at_threeAddr().

virtual void Walker::at_struct structNode the_struct,
Order  ord
[inline, virtual]
 

Definition at line 263 of file walker.h.

References at_sue().

virtual void Walker::at_subdecl subdeclNode the_subdecl,
Order  ord
[inline, virtual]
 

Definition at line 236 of file walker.h.

References at_decl().

virtual void Walker::at_sue sueNode the_sue,
Order  ord
[inline, virtual]
 

Reimplemented in id_lookup_walker, print_walker, and has_struct_walker.

Definition at line 260 of file walker.h.

References at_type().

Referenced by at_enum(), at_struct(), and at_union().

virtual void Walker::at_suespec suespecNode the_suespec,
Order  ord
[inline, virtual]
 

Reimplemented in scope_walker, semcheck_walker, sue_complete_walker, print_walker, and UnificationBasedPtr.

Definition at line 272 of file walker.h.

References at_type().

virtual void Walker::at_switch switchNode the_switch,
Order  ord
[inline, virtual]
 

Reimplemented in set_container_walker, TreeChecker, ProcWalker, print_walker, and init_flowproblem_walker.

Definition at line 335 of file walker.h.

References at_selection().

virtual void Walker::at_target targetNode the_target,
Order  ord
[inline, virtual]
 

Reimplemented in init_flowproblem_walker.

Definition at line 320 of file walker.h.

References at_stmt().

Referenced by at_case(), and at_label().

virtual void Walker::at_tdef tdefNode the_tdef,
Order  ord
[inline, virtual]
 

Reimplemented in id_lookup_walker, ref_fix_walker, TreeChecker, and print_walker.

Definition at line 248 of file walker.h.

References at_type().

virtual void Walker::at_ternary ternaryNode the_ternary,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 299 of file walker.h.

References at_expr().

virtual void Walker::at_text textNode the_text,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker.

Definition at line 377 of file walker.h.

References at_node().

virtual void Walker::at_threeAddr threeAddrNode the_3addr,
Order  ord
[inline, virtual]
 

Reimplemented in Linker, TreeChecker, print_walker, LivenessWalker, LivenessComments, and UnificationBasedPtr.

Definition at line 374 of file walker.h.

References at_stmt().

virtual void Walker::at_type typeNode the_type,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker.

Definition at line 242 of file walker.h.

References at_node().

Referenced by at_array(), at_func(), at_prim(), at_ptr(), at_sue(), at_suespec(), and at_tdef().

virtual void Walker::at_unary unaryNode the_unary,
Order  ord
[inline, virtual]
 

Reimplemented in TreeChecker, and print_walker.

Definition at line 290 of file walker.h.

References at_expr().

virtual void Walker::at_union unionNode the_union,
Order  ord
[inline, virtual]
 

Definition at line 266 of file walker.h.

References at_sue().

virtual void Walker::at_unit unitNode the_unit,
Order  ord
[inline, virtual]
 

Reimplemented in gcWalker, TreeChecker, print_walker, and UnificationBasedPtr.

Definition at line 227 of file walker.h.

References at_node().

virtual void Walker::at_while whileNode the_while,
Order  ord
[inline, virtual]
 

Reimplemented in print_walker.

Definition at line 341 of file walker.h.

References at_loop().

Depth Walker::depth  )  const [inline]
 

Return which Nodes of an AST should be visited.

A value of SubTree specifies that the entire AST should be traversed. A value of NodeOnly specifies that only the root Node in the AST should be visited.

Definition at line 211 of file walker.h.

References _depth.

Order Walker::order  )  const [inline]
 

Return the order in which Nodes of an AST should be visited.

Nodes can be visited before their children (Preorder), after their children (Postorder), or both (Both).

Definition at line 203 of file walker.h.

References _order.

Referenced by df_number_walker::at_node().


Member Data Documentation

Depth Walker::_depth [private]
 

Which Nodes in the AST should be visited.

Definition at line 166 of file walker.h.

Referenced by depth().

Order Walker::_order [private]
 

The order in which AST Nodes should be visited.

Definition at line 163 of file walker.h.

Referenced by order().


The documentation for this class was generated from the following file:

Generated on February 1, 2006
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