NReco LambdaParser

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.

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• PCL (Portable) library: can be used with any .NET target: net40+sl5, net45+wp8+win8+wpa81, .NET Standards 1.3 (.NET Core apps)
• any number of variables (values can be provided as dictionary or by callback delegate)
• supports arithmetic operations (+, -, *, /, %), comparisons (==, !=, >, <, >=, <=), conditionals including (ternary) operator ( ? : )
• 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}

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)

Custom values comparison

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); 

Who is using this?

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

License

Copyright 2016-2020 Vitaliy Fedorchenko

Distributed under the MIT license