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With inspiration from other libraries
There is a newer version: 2.12.15
package org.mvel2.ast;

import org.mvel2.CompileException;
import org.mvel2.MVEL;
import org.mvel2.ParserContext;
import org.mvel2.compiler.ExecutableStatement;
import org.mvel2.integration.VariableResolverFactory;
import org.mvel2.util.ParseTools;

import java.io.Serializable;
import java.math.BigDecimal;
import java.math.BigInteger;

import static org.mvel2.util.ParseTools.boxPrimitive;

public class Sign extends ASTNode {
  private Signer signer;
  private ExecutableStatement stmt;

  public Sign(char[] expr, int start, int end, int fields, ParserContext pCtx) {
    super(pCtx);
    this.expr = expr;
    this.start = start + 1;
    this.offset = end - 1;
    this.fields = fields;

    if ((fields & COMPILE_IMMEDIATE) != 0) {
      stmt = (ExecutableStatement) ParseTools.subCompileExpression(expr, this.start, this.offset, pCtx);

      egressType = stmt.getKnownEgressType();

      if (egressType != null && egressType != Object.class) {
        initSigner(egressType);
      }
    }
  }

  public ExecutableStatement getStatement() {
    return stmt;
  }

  @Override
  public Object getReducedValueAccelerated(Object ctx, Object thisValue, VariableResolverFactory factory) {
    return sign(stmt.getValue(ctx, thisValue, factory));
  }

  @Override
  public Object getReducedValue(Object ctx, Object thisValue, VariableResolverFactory factory) {
    return sign(MVEL.eval(expr, start, offset, thisValue, factory));
  }

  private Object sign(Object o) {
    if (o == null) return null;
    if (signer == null) {
      if (egressType == null || egressType == Object.class) egressType = o.getClass();
      initSigner(egressType);
    }
    return signer.sign(o);
  }

  private void initSigner(Class type) {
    if (Integer.class.isAssignableFrom(type = boxPrimitive(type))) signer = new IntegerSigner();
    else if (Double.class.isAssignableFrom(type)) signer = new DoubleSigner();
    else if (Long.class.isAssignableFrom(type)) signer = new LongSigner();
    else if (Float.class.isAssignableFrom(type)) signer = new FloatSigner();
    else if (Short.class.isAssignableFrom(type)) signer = new ShortSigner();
    else if (BigInteger.class.isAssignableFrom(type)) signer = new BigIntSigner();
    else if (BigDecimal.class.isAssignableFrom(type)) signer = new BigDecSigner();
    else {
      throw new CompileException("illegal use of '-': cannot be applied to: " + type.getName(), expr, start);
    }

  }


  private interface Signer extends Serializable {
    public Object sign(Object o);
  }

  private class IntegerSigner implements Signer {
    public Object sign(Object o) {
      return -((Integer) o);
    }
  }

  private class ShortSigner implements Signer {
    public Object sign(Object o) {
      return -((Short) o);
    }
  }

  private class LongSigner implements Signer {
    public Object sign(Object o) {
      return -((Long) o);
    }
  }

  private class DoubleSigner implements Signer {
    public Object sign(Object o) {
      return -((Double) o);
    }
  }

  private class FloatSigner implements Signer {
    public Object sign(Object o) {
      return -((Float) o);
    }
  }

  private class BigIntSigner implements Signer {
    public Object sign(Object o) {
      return new BigInteger(String.valueOf(-(((BigInteger) o).longValue())));
    }
  }

  private class BigDecSigner implements Signer {
    public Object sign(Object o) {
      return new BigDecimal(-((BigDecimal) o).doubleValue());
    }
  }


  @Override
  public boolean isIdentifier() {
    return false;
  }
}