Numeric Values

  • Universal Expression Parser parses expression items that have numeric format to expression items of type UniversalExpressionParser.ExpressionItems.INumericExpressionItem. The format of expression items that will be parsed to UniversalExpressionParser.ExpressionItems.INumericExpressionItem is determined by property IReadOnlyList<NumericTypeDescriptor> NumericTypeDescriptors { get; } in interface UniversalExpressionParser.IExpressionLanguageProvider, an instance of which is passed to the parser.

Click here to see the definition of UniversalExpressionParser.NumericTypeDescriptor

Click here to see the definition of UniversalExpressionParser.ExpressionItems.INumericExpressionItem

  • The parser scans the regular expressions in list in property IReadOnlyList<string> RegularExpressions { get; } in type NumericTypeDescriptor for each provided instance of UniversalExpressionParser.NumericTypeDescriptor to try to parse the expression to numeric expression item of type UniversalExpressionParser.ExpressionItems.INumericExpressionItem.

  • The abstract class UniversalExpressionParser.ExpressionLanguageProviderBase that can be used as a base class for implementations of UniversalExpressionParser.IExpressionLanguageProvider in most cases, implements the property NumericTypeDescriptors as a virtual property. The implementation of property NumericTypeDescriptors in UniversalExpressionParser.ExpressionLanguageProviderBase is demonstrated below, and it can be overridden to provide different format for numeric values:

Note

The regular expressions used in implementation of property NumericTypeDescriptors should always start with ‘^’ and should never end with ‘$’.

 1public virtual IReadOnlyList<NumericTypeDescriptor> NumericTypeDescriptors { get; } = new List<NumericTypeDescriptor>
 2{
 3    new NumericTypeDescriptor(KnownNumericTypeDescriptorIds.ExponentFormatValueId,
 4    new[] { @"^(\d+\.\d+|\d+\.|\.\d+|\d+)(EXP|exp|E|e)[+|-]?(\d+\.\d+|\d+\.|\.\d+|\d+)"}),
 5
 6    new NumericTypeDescriptor(KnownNumericTypeDescriptorIds.FloatingPointValueId,
 7    new[] { @"^(\d+\.\d+|\d+\.|\.\d+)"}),
 8
 9    new NumericTypeDescriptor(KnownNumericTypeDescriptorIds.IntegerValueId, new[] { @"^\d+" })
10}

  • The first regular expression that matches the expression, is stored in properties SucceededNumericTypeDescriptor of type UniversalExpressionParser.NumericTypeDescriptor and IndexOfSucceededRegularExpression in parsed expression item of type UniversalExpressionParser.ExpressionItems.INumericExpressionItem.

  • The numeric value is stored as text in property INameExpressionItem Value in text format. Therefore, there is no limit on numeric value digits.

  • The expression evaluator that uses the Universal Expression Parser can convert the textual value in property Value of type INameExpressionItem in UniversalExpressionParser.ExpressionItems.INumericExpressionItem to a value of numeric type (int, long, double, etc.).

  • Examples of numeric value expression items are demonstrated below:

1// By default exponent notation can be used.
2println(-0.5e-3+.2exp3.4+3.E2.7+2.1EXP.3);
3println(.5e15*x);
4
5// Numeric values can have no limitations on the number of digits. The value is stored as text in
6// UniversalExpressionParser.ExpressionItems.INumericExpressionItem.
7// The text can be validated farther and converted to numeric values by the expression evaluator that
8// uses the parser.
9var x = 2.3*x+123456789123456789123456789123456789;

Click here to see the visualized instance of UniversalExpressionParser.IParseExpressionResult