  ## Evaluation

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Let us consider approaches to compute an expression.

## Evaluation

All constant types, such as booleans and numbers, have their own types in the AM's type hierarchy. When evaluating, you will also get a result in one of these types. To evaluate an Entity you need to call its method EvalNumerical to evaluate it into a Complex and EvalBoolean to evaluate it into a Boolean. Example:
Entity expr = "2 + 3";
Console.WriteLine(expr.EvalNumerical()); // 5
Entity expr2 = "true implies false";
Console.WriteLine(expr2.EvalBoolean()); // false
If the given expression cannot be represented as the requested type, for example, the result is a set, or the expression contains unresolved variables, exception CannotEvalException. Example:
Entity expr = "2 + 3 + a";
Console.WriteLine(expr.EvalNumerical()); // throws, as "a" is unknown
Entity expr2 = "{ 1, 3 }";
Console.WriteLine(expr2.EvalNumerical()); // throws, as the result is not a number
Entity expr3 = "true implies b";
Console.WriteLine(expr3.EvalBoolean()); // throws, as "b" is unknown
Properties EvaluableBoolean and EvaluableNumerical show whether the expression can be expressed as a single boolean or a single numerical value. For example, do not call EvalNumerical() if EvaluableNumerical is false. Once evaluated, the result might be converted into a primitive via explicit cast. Example:
Entity expr = "3 / 5";
double evalDouble = (double)expr.EvalNumerical();
Console.WriteLine(evalDouble);
Complex evalComplex = (Complex)expr.EvalNumerical();
Console.WriteLine(evalComplex);
int evalInt = (int)expr.EvalNumerical();
Console.WriteLine(evalInt);
Output:
0.6
(0.6, 0)
0
If a number cannot be converted into the given primitive, a NumberCastException will be thrown. Example:
Entity expr = "3 / 5 + i";
double evalDouble = (double)expr.EvalNumerical(); // throws NumberCastException
However, if you do not need the final number, but instead, the "most" evaluated expression, you may address property Evaled. Example:
Entity expr = "2 + 3";
Console.WriteLine(expr.Evaled);
Entity expr2 = "2 + 3 + a";
Console.WriteLine(expr2.Evaled);
Output:
5
5 + a
It is recommended to consider Evaled as a free-to-access property. It is a so-called lazy property. Nonetheless, it should be pointed out that the first address of this property executes computations and puts into cache. Extensions: string.EvalNumerical(), string.EvalBoolean().

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