PrependTo.java :  » Algebra » symja » org » matheclipse » core » reflection » system » Java Open Source

package org.matheclipse.core.reflection.system;

import org.matheclipse.core.eval.interfaces.AbstractFunctionEvaluator;
import org.matheclipse.core.expression.IConstantHeaders;
import org.matheclipse.core.interfaces.IAST;
import org.matheclipse.core.interfaces.IExpr;
import org.matheclipse.core.interfaces.ISymbol;

import com.google.common.base.Function;

public class PrependTo extends AbstractFunctionEvaluator implements IConstantHeaders {

  class PrependToFunction implements Function<IExpr, IExpr> {
    private final IExpr value;

    public PrependToFunction(final IExpr value) {
      this.value = value;
    }

    @Override
    public IExpr apply(final IExpr symbolValue) {
      if (!symbolValue.isAST()) {
        return null;
      }
      final IAST f0 = ((IAST) symbolValue).clone();
      f0.add(1, value);
      return f0;
    }

  }

  public PrependTo() {
    super();
  }

  @Override
  public IExpr evaluate(final IAST ast) {
    if ((ast.size() == 3) && (ast.get(1).isSymbol())) {
      Function<IExpr, IExpr> function = new PrependToFunction(ast.get(2));
      final ISymbol sym = (ISymbol) ast.get(1);
      IExpr[] results = sym.reassignSymbolValue(function);
      if (results != null) {
        return results[1];
      }
    }

    return null;
  }

  @Override
  public void setUp(final ISymbol symbol) {
    symbol.setAttributes(ISymbol.HOLDFIRST);
  }
}