Runtime parser for string expressions (formulas, method calls, properties/fields/arrays accessors). LambdaParser builds dynamic LINQ expression tree and compiles it to the lambda delegate. Types are resolved at run-time like in dynamic languages.

NuGet	Windows x64	Linux

• can be used in any .NET app: net45 (legacy .NET Framework apps), netstandard1.3 (.NET Core apps), netstandard2.0 (all modern .NET apps).
• any number of expression arguments (values can be provided as dictionary or by callback delegate)
• supports arithmetic operations (+, -, *, /, %), comparisons (==, !=, >, <, >=, <=), conditionals including (ternary) operator ( boolVal ? whenTrue : whenFalse )
• access object properties, call methods and indexers, invoke delegates
• dynamic typed variables: performs automatic type conversions to match method signature or arithmetic operations
• create arrays and dictionaries with simplified syntax: new dictionary{ {"a", 1}, {"b", 2} } , new []{ 1, 2, 3}
• local variables that may go before main expression: var a = 5; var b = contextVar/total*100; (disabled by default, to enable use LambdaParser.AllowVars property)

Nuget package: NReco.LambdaParser

var lambdaParser = new NReco.Linq.LambdaParser();

var varContext = new Dictionary<string,object>();
varContext["pi"] = 3.14M;
varContext["one"] = 1M;
varContext["two"] = 2M;
varContext["test"] = "test";
Console.WriteLine( lambdaParser.Eval("pi>one && 0<one ? (1+8)/3+1*two : 0", varContext) ); // --> 5
Console.WriteLine( lambdaParser.Eval("test.ToUpper()", varContext) ); // --> TEST

(see unit tests for more expression examples)

By default LambdaParser uses ValueComparer for values comparison. You can provide your own implementation or configure its option to get desired behaviour:

• ValueComparer.NullComparison determines how comparison with null is handled. 2 options:
  • MinValue: null is treated as minimal possible value for any type - like .NET IComparer
  • Sql: null is not comparable with any type, including another null - like in SQL
• ValueComparer.SuppressErrors allows to avoid convert exception. If error appears during comparison exception is not thrown and this means that values are not comparable (= any condition leads to false).

var valComparer = new ValueComparer() { NullComparison = ValueComparer.NullComparisonMode.Sql };
var lambdaParser = new LambdaParser(valComparer); 

NReco.LambdaParser is in production use at SeekTable.com and PivotData microservice (used for user-defined calculated cube members: formulas, custom formatting).

Copyright 2016-2024 Vitaliy Fedorchenko and contributors

Distributed under the MIT license