Add custom function to EvalEx

EvalEx_CustomFunction.java

package evaluation;

import com.ezylang.evalex.EvaluationException;
import com.ezylang.evalex.Expression;
import com.ezylang.evalex.config.ExpressionConfiguration;
import com.ezylang.evalex.data.EvaluationValue;
import com.ezylang.evalex.functions.AbstractFunction;
import com.ezylang.evalex.functions.FunctionParameter;
import com.ezylang.evalex.parser.Token;
import lombok.extern.slf4j.Slf4j;

import java.util.*;

@FunctionParameter(name = "value", isVarArg = true)
class IsNumberFunction extends AbstractFunction {
    public static final String NAME = "IS_NUMBER";

    @Override
    public EvaluationValue evaluate(Expression expression, Token functionToken, EvaluationValue... parameterValues) throws EvaluationException {
        if (parameterValues.length != 1)
            throw new EvaluationException(functionToken, "%s requires exactly one parameter.".formatted(NAME));

        try {
            Double.parseDouble(parameterValues[0].getStringValue());
            return EvaluationValue.booleanValue(true);
        } catch (NumberFormatException e) {
            return EvaluationValue.booleanValue(false);
        }
    }
}

@Slf4j
public class Main {
    @lombok.SneakyThrows
    public static void main(String[] args) {
        var configuration = ExpressionConfiguration.builder()
                //.mathContext()
                .build()
                .withAdditionalFunctions(
                        Map.entry(IsNumberFunction.NAME, new IsNumberFunction())
                );
        Expression expression = new Expression("IF(IS_NUMBER(value), value < 5.0, NULL)", configuration)
                .with("value", 5.0)
                //.with("value", "ATMF")
                ;

        EvaluationValue result = expression.evaluate();

        System.out.println(result.getBooleanValue());
    }
}

pom.xml

 <dependency>
            <groupId>com.ezylang</groupId>
            <artifactId>EvalEx</artifactId>
            <version>3.4.0</version>
        </dependency>