//Exp( p ) is
// var t : Tree
// t := P
// while next is a binary operator and prec(binary(next)) >= p
// const op := binary(next)
// consume
// const q := case associativity(op)
// of Right: prec( op )
// Left: 1+prec( op )
// const t1 := Exp( q )
// t := mkNode( op, t, t1)
// return t
private Expression Exp(int p)
{
Expression l = P();
Operator op = new Operator();
while (true)
{
if (IsBinaryOperator(tokens.Tok, ref op) && Precedence(op) >= p)
{
tokens.Consume();
int q = Precedence(op) + (IsLeftAssociative(op) ? 1 : 0);
Expression r = Exp(q);
l = Binary.New(op, l, r);
}
else if (IsUnaryPostOperator(tokens.Tok, ref op) && Precedence(op) >= p)
{
tokens.Consume();
l = Unary.New(op, l);
}
else
{
break;
}
}
return(l);
}
private static Expression Split(Expression P)
{
int child = 0;
if (P is Sum)
{
return(ComputerAlgebra.Sum.New(((ComputerAlgebra.Sum)P).Terms.Select(i => ChildPattern(ref child))));
}
if (P is Product)
{
return(Product.New(((Product)P).Terms.Select(i => ChildPattern(ref child))));
}
if (P is Binary)
{
return(Binary.New(((Binary)P).Operator, ChildPattern(ref child), ChildPattern(ref child)));
}
if (P is Unary)
{
return(Unary.New(((Unary)P).Operator, ChildPattern(ref child)));
}
if (P is Call)
{
return(Call.New(((Call)P).Target, ((Call)P).Arguments.Select(i => ChildPattern(ref child))));
}
return(null);
}
/// <summary>
/// Distribute products across sums, using partial fractions if necessary.
/// </summary>
/// <param name="x"></param>
/// <returns></returns>
public static Expression Expand(this Expression f, Expression x)
{
if (f is Product)
{
return(ExpandMultiply(f, x));
}
else if (f is Sum)
{
return(Sum.New(((Sum)f).Terms.Select(i => i.Expand(x))));
}
else if (f is Power)
{
return(ExpandPower((Power)f, x));
}
else if (f is Binary)
{
return(Binary.New(((Binary)f).Operator, ((Binary)f).Left.Expand(), ((Binary)f).Right.Expand()));
}
else if (f is Unary)
{
return(Unary.New(((Unary)f).Operator, ((Unary)f).Operand.Expand()));
}
return(f);
}
/// <summary>
/// Distribute products across sums, using partial fractions if necessary.
/// </summary>
/// <param name="x"></param>
/// <returns></returns>
public static Expression Expand(this Expression f, Expression x)
{
if (f is Product)
{
return(ExpandMultiply(f, x));
}
else if (f is Sum sum)
{
return(Sum.New(sum.Terms.Select(i => i.Expand(x))));
}
else if (f is Power power)
{
return(ExpandPower(power, x));
}
else if (f is Binary binary)
{
return(Binary.New(binary.Operator, binary.Left.Expand(x), binary.Right.Expand(x)));
}
else if (f is Unary unary)
{
return(Unary.New(unary.Operator, unary.Operand.Expand()));
}
return(f);
}
protected override Expression VisitBinary(Binary B)
{
Expression L = Visit(B.Left);
Expression R = Visit(B.Right);
if (ReferenceEquals(L, null) || ReferenceEquals(R, null))
{
return(null);
}
if (ReferenceEquals(L, B.Left) && ReferenceEquals(R, B.Right))
{
return(B);
}
else
{
return(Binary.New(B.Operator, L, R));
}
}
protected override Expression VisitBinary(Binary B)
{
Expression L = Visit(B.Left);
Expression R = Visit(B.Right);
// Evaluate substitution operators.
if (B is Substitute)
{
return(Visit(L.Substitute(Set.MembersOf(R).Cast <Arrow>())));
}
Real?LR = AsReal(L);
Real?RR = AsReal(R);
// Evaluate relational operators on constants.
if (LR != null && RR != null)
{
switch (B.Operator)
{
case Operator.Equal: return(Constant.New(LR.Value == RR.Value));
case Operator.NotEqual: return(Constant.New(LR.Value != RR.Value));
case Operator.Less: return(Constant.New(LR.Value < RR.Value));
case Operator.Greater: return(Constant.New(LR.Value <= RR.Value));
case Operator.LessEqual: return(Constant.New(LR.Value > RR.Value));
case Operator.GreaterEqual: return(Constant.New(LR.Value >= RR.Value));
case Operator.ApproxEqual: return(Constant.New(
LR.Value == RR.Value ||
Real.Abs(LR.Value - RR.Value) < 1e-12 * Real.Max(Real.Abs(LR.Value), Real.Abs(RR.Value))));
}
}
// Evaluate boolean operators if possible.
switch (B.Operator)
{
case Operator.And:
if (IsFalse(LR) || IsFalse(RR))
{
return(Constant.New(false));
}
else if (IsTrue(LR) && IsTrue(RR))
{
return(Constant.New(true));
}
break;
case Operator.Or:
if (IsTrue(LR) || IsTrue(RR))
{
return(Constant.New(true));
}
else if (IsFalse(LR) && IsFalse(RR))
{
return(Constant.New(false));
}
break;
case Operator.Equal:
case Operator.ApproxEqual:
if (L.Equals(R))
{
return(Constant.New(true));
}
break;
case Operator.NotEqual:
if (L.Equals(R))
{
return(Constant.New(false));
}
break;
}
return(Binary.New(B.Operator, L, R));
}
