Expression Engine Library
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Expression Engine Library alfa.

This project is a simple mathematical expression parser written in C#. It's the refactoring of an old project and uses an AST-evaluation algorithm. You can use built-in or add your functions and variables to global scope. It was written primarily for fun and and as programming exercise; anyway if you anyone find it useful, please send feature requests or issues; but please take note that this is still a work in progress.

At the moment specification is just a draft.

To build:

MonoDevelop or Visual Studio.

At glance:

var contex = new Context()
  .SetVariable("G", 6.67428D)
  .SetVariable("earth_mass", Evaluate.As<double>("5.97219 * pow(10,24)")) // 5.97219E+24 kg
  .SetVariable("lunar_mass", Evaluate.As<double>("7.34767309 * pow(10,22)")) // 7.34767309E+22 kg
  .SetVariable("perigee_dist", 356700000D) // moon-earth distance at perigee in m
  .SetFunction("calc_force", (object[] args) => ((double) args[0] * (double) args[1]) / Math.Pow((double) args[2], 2));
var result = contex.EvaluateAs<double>("G * calc_force(earth_mass, lunar_mass, perigee_dist)"); // 2.3018745174107073E+31
bool isGCorrect = contex.EvaluateAs<bool>("G == 6.67428");



  • String literals fully implemented.
  • Version policy changed.
  • First changes to lexer for handle string literals.
  • Refactoring, ExpressionEvaluator splitted in Context (as the name, evaluation with context) and Evaluator (static helper, contextless evaluation).
  • Added support for exponent in numeric literal ([E|e][+|-][DIGIT]).
  • Parser class aligned to new grammar.
  • BNF grammar changed (see Evaluator.grm).
  • Operator ^ (exponent) removed. Will be used as bitwise operator.
  • Introduced relational operators (==, !=, <, >, <=, >=).
  • Introduced true and false literals.
  • Heavy internal refactoring toward a new design.
  • Evaluation provided via both instance and static methods.


Giacomo Stelluti Scala