yacasevaluator.java

计算机代数系统

package net.sf.yacas;


// new-style evaluator, passing arguments onto the stack in LispEnvironment

class YacasEvaluator extends EvalFuncBase
{
  // FunctionFlags can be orred when passed to the constructor of this function

  static int Function=0;    // Function: evaluate arguments
  static int Macro=1;       // Function: don't evaluate arguments
  static int Fixed = 0;     // fixed number of arguments
  static int Variable = 2;  // variable number of arguments

  public YacasEvaluator(YacasEvalCaller aCaller,int aNrArgs, int aFlags)
  {
    iCaller = aCaller;
    iNrArgs = aNrArgs;
    iFlags = aFlags;
  }
  public void Evaluate(LispPtr aResult,LispEnvironment aEnvironment, LispPtr aArguments) throws Exception
  {
  if ((iFlags & Variable) == 0)
  {
    LispError.CheckNrArgs(iNrArgs+1,aArguments,aEnvironment);
  }

  int stacktop = aEnvironment.iStack.GetStackTop();

  // Push a place holder for the result: push full expression so it is available for error reporting
  aEnvironment.iStack.PushArgOnStack(aArguments.Get());

  LispIterator iter = new LispIterator(aArguments);
  iter.GoNext();

  int i;
  int nr = iNrArgs;

  if ((iFlags & Variable) != 0) nr--;

  // Walk over all arguments, evaluating them as necessary
  if ((iFlags & Macro) != 0)
  {
    for (i=0;i<nr;i++)
    {
      LispError.Check(iter.GetObject() != null, LispError.KLispErrWrongNumberOfArgs);
      aEnvironment.iStack.PushArgOnStack(iter.GetObject().Copy(false));
      iter.GoNext();
    }
    if ((iFlags & Variable) != 0)
    {
      LispPtr head = new LispPtr();
      head.Set(aEnvironment.iList.Copy(false));
      head.Get().Next().Set(iter.GetObject());
      aEnvironment.iStack.PushArgOnStack(LispSubList.New(head.Get()));
    }
  }
  else
  {
    LispPtr arg = new LispPtr();
    for (i=0;i<nr;i++)
    {
      LispError.Check(iter.GetObject() != null, LispError.KLispErrWrongNumberOfArgs);
      LispError.Check(iter.Ptr() != null, LispError.KLispErrWrongNumberOfArgs);
      aEnvironment.iEvaluator.Eval(aEnvironment, arg, iter.Ptr());
      aEnvironment.iStack.PushArgOnStack(arg.Get());
      iter.GoNext();
    }
    if ((iFlags & Variable) != 0)
    {

//LispString res;

//printf("Enter\n");
      LispPtr head = new LispPtr();
      head.Set(aEnvironment.iList.Copy(false));
      head.Get().Next().Set(iter.GetObject());
      LispPtr list = new LispPtr();
      list.Set(LispSubList.New(head.Get()));


/*
PrintExpression(res, list,aEnvironment,100);
printf("before %s\n",res.String());
*/

      aEnvironment.iEvaluator.Eval(aEnvironment, arg, list);

/*
PrintExpression(res, arg,aEnvironment,100);
printf("after %s\n",res.String());
*/

      aEnvironment.iStack.PushArgOnStack(arg.Get());
//printf("Leave\n");
    }
  }

  iCaller.Eval(aEnvironment,stacktop);  
  aResult.Set(aEnvironment.iStack.GetElement(stacktop).Get());
  aEnvironment.iStack.PopTo(stacktop);
  }
  YacasEvalCaller iCaller;
  int iNrArgs;
  int iFlags;
}