Query.java

package javaf.syb;

import javaf.prelude.*;

import java.lang.reflect.*;
import java.util.List;

public class Query {

    /**
     * Apply a type-specific function if possible; apply generic function otherwise.
     */
    public static <X,Y> Function<Object,Y> or(final Function<X,Y> f, final Function<Object,Y> otherwise) {
        return new Function<Object,Y>() {

            @SuppressWarnings("unchecked")
            public Y apply(Object x) {
                try { 
                    return f.apply((X)x);
                }
                catch (ClassCastException _) {
                    return otherwise.apply(x);
                }
            }
        };
    }

    /**
     * Apply a function if possible; return default otherwise.
     */
    public static <X,Y> Function<Object,Y> orDefault(final Function<X,Y> f, final Y otherwise) {
        return or(f, new Function<Object,Y>() { public Y apply(Object x) { return otherwise; }});
    }

    /**
     * Apply a query to all immediate sub-objects.
     */
    public static <Y> Function<Object,Y> all(final Function<Object,Y> f, final BinaryOperator<Y> op, final Y initial) {
        return new Function<Object,Y>() {
            @SuppressWarnings("rawtypes")
            public Y apply(Object x) {
                Y y = initial;
                // Special case for lists
                if (x instanceof List)
                    for (Object o : (List)x)
                        y = op.apply(y, f.apply(o));
                else {
                    // Regular case based on getters
                    for (Method m : x.getClass().getDeclaredMethods()) {
                        if (m.getName().startsWith("get") 
                        && m.getParameterTypes().length == 0) {
                            try {
                                y = op.apply(y, f.apply(m.invoke(x, new Object[]{})));
                            }
                            catch (IllegalAccessException e) {
                                // assert "DEAD CODE"
                            } catch (IllegalArgumentException e) {
                                // assert "DEAD CODE"
                            } catch (InvocationTargetException e) {
                                // assert "DEAD CODE"
                            }
                        }
                    }
                }
                return y;
            }
        };
    }

    /**
     * Apply a function to each and every sub-object in bottom-up manner.
     */
    public static <Y> Function<Object,Y> everything(final Function<Object,Y> f, final BinaryOperator<Y> op, final Y initial) {
        return new Function<Object,Y>() {
            public Y apply(Object x) {
                return op.apply(f.apply(x), all(everything(f, op, initial), op, initial).apply(x));
            }
        };
    }
}