internal static InstructAST Build(InstructAST left, InstructAST right)
{
// a && a == a
if (left.Equals(right)) return left;
// <empty> && a == a && <empty> == a if zero-width, <fail> otherwise
if (left == EmptyAST.Instance)
return right.IsZeroWidth ? right : AnyCharAST.Negate;
if (right == EmptyAST.Instance)
return left.IsZeroWidth ? left : AnyCharAST.Negate;
// When a contains b, a && b == b
if (left.Contains(right)) return right;
// When b contains a, a && b == a
if (right.Contains(left)) return left;
// When a and b are disjoint, a && b matches nowhere
if (left.DisjointWith(right)) return AnyCharAST.Negate;
// !a && !b == !(a || b), !a && b == b -- a, a && !b == a -- b
NotTestAST negLeft = left as NotTestAST;
NotTestAST negRight = right as NotTestAST;
if (negLeft != null)
{
if (negRight != null)
return NotTestAST.Make(OrTestAST.Make(negLeft.Argument, negRight.Argument));
else
return DiffTestAST.Make(right, negLeft.Argument);
}
else if (negRight != null)
return DiffTestAST.Make(left, negRight.Argument);
// (a && b) && c == a && (b && c)
AndTestAST andRight = right as AndTestAST;
if (andRight != null)
return AndTestAST.Make(AndTestAST.Make(left, andRight.Left), andRight.Right);
// (a || b) && c == (a && c) || (b && c)
OrTestAST orLeft = left as OrTestAST;
if (orLeft != null)
return OrTestAST.Make(AndTestAST.Make(orLeft.Left, right), AndTestAST.Make(orLeft.Right, right));
// a && (b || c) == (a && b) || (a && c)
if (!left.IsZeroWidth)
{
OrTestAST orRight = right as OrTestAST;
if (orRight != null)
return OrTestAST.Make(AndTestAST.Make(left, orRight.Left), AndTestAST.Make(left, orRight.Right));
}
// Intersection of overlapping ranges is the overlap
CharRangeAST leftRange = left as CharRangeAST;
CharRangeAST rightRange = right as CharRangeAST;
if (leftRange != null && rightRange != null && (leftRange.FoldsCase == rightRange.FoldsCase))
{
int low = Math.Max(leftRange.Min, rightRange.Min);
int high = Math.Min(leftRange.Max, rightRange.Max);
return CharRangeAST.Make(low, high, leftRange.FoldsCase);
}
return new AndTestAST(left, right);
}
internal static InstructAST Build(InstructAST left, InstructAST right)
{
// a -- a == <fail>
if (left.Equals(right)) return AnyCharAST.Negate;
// When b contains a, a -- b matches no codepoints
if (right.Contains(left)) return AnyCharAST.Negate;
// When a and b are disjoint, a -- b == a
if (left.DisjointWith(right)) return left;
// \p{Any} -- a == !a
if (AnyCharAST.Instance.Equals(left)) return NotTestAST.Make(right);
// !a -- !b == b -- a; !a -- b == !(a || b); a -- !b == a && b
NotTestAST negLeft = left as NotTestAST;
NotTestAST negRight = right as NotTestAST;
if (negLeft != null)
{
if (negRight != null)
return DiffTestAST.Make(negRight.Argument, negLeft.Argument);
else
return NotTestAST.Make(OrTestAST.Make(negLeft.Argument, right));
}
else if (negRight != null)
return AndTestAST.Make(left, negRight.Argument);
// (a -- b) -- c == a -- (b || c)
DiffTestAST diffLeft = left as DiffTestAST;
if (diffLeft != null)
return DiffTestAST.Make(diffLeft.Left, OrTestAST.Make(diffLeft.Right, right));
// (a || b) -- c == (a -- c) || (b -- c)
OrTestAST orLeft = left as OrTestAST;
if (orLeft != null)
return OrTestAST.Make(DiffTestAST.Make(orLeft.Left, right), DiffTestAST.Make(orLeft.Right, right));
// When a and b are overlapping ranges, a -- b == a with a gap
CharRangeAST leftRange = left as CharRangeAST;
if (leftRange != null)
{
int excludeMin = -1;
int excludeMax = -1;
OneCharAST rightChar = right as OneCharAST;
if (rightChar != null && (leftRange.FoldsCase == rightChar.FoldsCase))
{
excludeMin = excludeMax = rightChar.Character;
}
CharRangeAST rightRange = right as CharRangeAST;
if (rightRange != null && (leftRange.FoldsCase == rightRange.FoldsCase))
{
excludeMin = rightRange.Min;
excludeMax = rightRange.Max;
}
if (leftRange.Min <= excludeMax && excludeMin <= leftRange.Max)
return OrTestAST.Make(CharRangeAST.Make(leftRange.Min, excludeMin - 1, leftRange.FoldsCase),
CharRangeAST.Make(excludeMax + 1, leftRange.Max, leftRange.FoldsCase));
}
return new DiffTestAST(left, right);
}