CS143-Lab/include/PA5/symtab.h

//
// See copyright.h for copyright notice and limitation of liability
// and disclaimer of warranty provisions.
//
#include "copyright.h"

// The symbol table package.
//
// Create a symbol table with :
// SymbolTable<thing to look up on, info to store> name();
//
// You must enter a scope before adding anything to the symbol table.

#ifndef _SYMTAB_H_
#define _SYMTAB_H_

#include "list.h"

//
// SymtabEnty<SYM,DAT> defines the entry for a symbol table that associates
//    symbols of type `SYM' with data of type `DAT *'.  
//

template <class SYM, class DAT>
class SymtabEntry {
private:
  SYM id;        // the key field
  DAT *info;     // associated information for the symbol
public:
  SymtabEntry(SYM x, DAT *y) : id(x), info(y) { }
  SYM get_id() const    { return id; }
  DAT *get_info() const { return info; }
};

//
// SymbolTable<SYM,DAT> describes a symbol table mapping symbols of
//    type `SYM' to data of type `DAT *'.  It is implemented as a
//    list of lists of `SymtabEntry<SYM,DAT> *'.  The inner list is
//    a scope, a mapping from symbols to data, and the outer list is
//    a list of scopes. 
//
//    `tbl' points to the current top scope.
//
//    `enterscope' makes the table point to a new scope whose parent
//       is the scope it pointed to previously.
//
//    `exitscope' makes the table point to the parent scope of the
//        current scope.  Note that the old child scope is not
//        deallocated.  One may save the state of a symbol table
//        at a given point by copying it with `operator ='
//
//    `addid(s,i)' adds a symbol table entry to the current scope of
//        the symbol table mapping symbol `s' to data `d'.  The old
//        top scope isn't modified; a new scope is created whose
//        entry list is the new entry followed by the old entry list,
//        and whose tail is the old top scope's parent.  The table
//        is made to point to this new scope.
//
//    `lookup(s)' looks for the symbol `s', starting at the top scope
//        and proceeding down the list of scopes until either an
//        entry is found whose `get_id()' equals `s', or the end of
//        the root scope is reached.  It returns the data item
//        associated with the entry, or NULL if no such entry exists.
//
//    
//    `probe(s)' checks the top scope for an entry whose `get_id()'
//        equals `s', and returns the entry's `get_info()' if
//        found, and NULL otherwise.
//
//    `dump()' prints the symbols in the symbol table.
//

template <class SYM, class DAT>
class SymbolTable
{
   typedef SymtabEntry<SYM,DAT> ScopeEntry;
   typedef List<ScopeEntry> Scope;
   typedef List<Scope> ScopeList;
private:
   ScopeList  *tbl;
public:
   SymbolTable(): tbl(NULL) { }     // create a new symbol table

   // Create pointer to current symbol table.
   SymbolTable &operator =(const SymbolTable &s) { tbl = s.tbl; return *this; }

   void fatal_error(char * msg)
   {
     cerr << msg << "\n";
     exit(1);
   } 

   // Enter a new scope.  A symbol table is organized as a list of
   // lists.  The head of the list is the innermost scope, the tail
   // holds the outer scopes.  A scope must be entered before anything
   // can be added to the table.

   void enterscope()
   {
       // The cast of NULL is required for template instantiation to work
       // correctly.
       tbl = new ScopeList((Scope *) NULL, tbl);
   }

   // Pop the first scope off of the symbol table.
   void exitscope()
   {
       // It is an error to exit a scope that doesn't exist.
       if (tbl == NULL) {
	   fatal_error("exitscope: Can't remove scope from an empty symbol table.");
       }
       tbl = tbl->tl();
   }

   // Add an item to the symbol table.
   ScopeEntry *addid(SYM s, DAT *i)
   {
       // There must be at least one scope to add a symbol.
       if (tbl == NULL) fatal_error("addid: Can't add a symbol without a scope.");
       ScopeEntry * se = new ScopeEntry(s,i);
       tbl = new ScopeList(new Scope(se, tbl->hd()), tbl->tl());
       return(se);
   }
   
   // Lookup an item through all scopes of the symbol table.  If found
   // it returns the associated information field, if not it returns
   // NULL.

   DAT * lookup(SYM s)
   {
       for(ScopeList *i = tbl; i != NULL; i=i->tl()) {
	   for( Scope *j = i->hd(); j != NULL; j = j->tl()) {
	       if (s == j->hd()->get_id()) {
		   return (j->hd()->get_info());
	       }
	   }
       }
       return NULL;
   }

   // probe the symbol table.  Check the top scope (only) for the item
   // 's'.  If found, return the information field.  If not return NULL.
   DAT *probe(SYM s)
   {
       if (tbl == NULL) {
	   fatal_error("probe: No scope in symbol table.");
       }
       for(Scope *i = tbl->hd(); i != NULL; i = i->tl()) {
	   if (s == i->hd()->get_id()) {
	       return(i->hd()->get_info());
	   }
       }
       return(NULL);
   }

   // Prints out the contents of the symbol table  
   void dump()
   {
      for(ScopeList *i = tbl; i != NULL; i = i->tl()) {
         cerr << "\nScope: \n";
         for(Scope *j = i->hd(); j != NULL; j = j->tl()) {
            cerr << "  " << j->hd()->get_id() << endl;
         }
      }
   }
 
};

#endif