GADT with ADT4J

GADT.java

/**
 *
 * @author Victor Nazarov <asviraspossible@gmail.com>
 */
public class GADT<T> extends GADTBase<GADT<Integer>, GADT<Boolean>, GADT<T>> {
    public static GADT<Integer> literal(int i) {
        return new GADT<Integer>(GADTBase.<GADT<Integer>, GADT<Boolean>, GADT<Integer>>_literal(i));
    }

    public static GADT<Integer> plus(GADT<Integer> a, GADT<Integer> b) {
        return new GADT<Integer>(GADTBase.<GADT<Integer>, GADT<Boolean>, GADT<Integer>>_plus(a, b));
    }

    public static GADT<Boolean> isLessOrEqual(GADT<Integer> a, GADT<Integer> b) {
        return new GADT<Boolean>(GADTBase.<GADT<Integer>, GADT<Boolean>, GADT<Boolean>>_isLessOrEqual(a, b));
    }

    public static <T> GADT<T> if_(GADT<Boolean> condition, GADT<T> iftrue, GADT<T> iffalse) {
        return new GADT<T>(GADTBase.<GADT<Integer>, GADT<Boolean>, GADT<T>>_if_(condition, iftrue, iffalse));
    }

    private GADT(GADTBase<GADT<Integer>, GADT<Boolean>, GADT<T>> base) {
        super(base);
    }

    public static Integer evalInt(GADT<Integer> term) {
        return acceptInt(term, new IntegerVisitor<Integer>() {
            @Override
            public Integer _literal(int i) {
                return i;
            }

            @Override
            public Integer _plus(GADT<Integer> a, GADT<Integer> b) {
                return evalInt(a) + evalInt(b);
            }

            @Override
            public Integer _if_(GADT<Boolean> condition, GADT<Integer> iftrue, GADT<Integer> iffalse) {
                return evalBool(condition) ? evalInt(iftrue) : evalInt(iffalse);
            }
        });
    }

    public static Boolean evalBool(GADT<Boolean> term) {
        return acceptBool(term, new BooleanVisitor<Boolean>() {
            @Override
            public Boolean _isLessOrEqual(GADT<Integer> a, GADT<Integer> b) {
                return evalInt(a) <= evalInt(b);
            }

            @Override
            public Boolean _if_(GADT<Boolean> condition, GADT<Boolean> iftrue, GADT<Boolean> iffalse) {
                return evalBool(condition) ? evalBool(iftrue) : evalBool(iffalse);
            }
        });
    }

    public static <R> R acceptInt(GADT<Integer> term, final IntegerVisitor<R> visitor) {
        return term.accept(new GADTBaseVisitor<GADT<Integer>, GADT<Boolean>, GADT<Integer>, R>() {
            @Override
            public R _literal(int i) {
                return visitor._literal(i);
            }

            @Override
            public R _plus(GADT<Integer> a, GADT<Integer> b) {
                return visitor._plus(a, b);
            }

            @Override
            public R _isLessOrEqual(GADT<Integer> a, GADT<Integer> b) {
                throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
            }

            @Override
            public R _if_(GADT<Boolean> condition, GADT<Integer> iftrue, GADT<Integer> iffalse) {
                return visitor._if_(condition, iftrue, iffalse);
            }
        });
    }

    public static <R> R acceptBool(GADT<Boolean> term, final BooleanVisitor<R> visitor) {
        return term.accept(new GADTBaseVisitor<GADT<Integer>, GADT<Boolean>, GADT<Boolean>, R>() {

            @Override
            public R _literal(int i) {
                throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
            }

            @Override
            public R _plus(GADT<Integer> a, GADT<Integer> b) {
                throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
            }

            @Override
            public R _isLessOrEqual(GADT<Integer> a, GADT<Integer> b) {
                return visitor._isLessOrEqual(a, b);
            }

            @Override
            public R _if_(GADT<Boolean> condition, GADT<Boolean> iftrue, GADT<Boolean> iffalse) {
                return visitor._if_(condition, iftrue, iffalse);
            }
        });
    }

    public interface IntegerVisitor<R> {
        R _literal(int i);
        R _plus(GADT<Integer> a, GADT<Integer> b);
        R _if_(GADT<Boolean> condition, GADT<Integer> iftrue, GADT<Integer> iffalse);
    }

    public interface BooleanVisitor<R> {
        R _isLessOrEqual(GADT<Integer> a, GADT<Integer> b);
        R _if_(GADT<Boolean> condition, GADT<Boolean> iftrue, GADT<Boolean> iffalse);
    }
}

GADTBaseVisitor.java

import com.github.sviperll.adt4j.GenerateValueClassForVisitor;

/**
 *
 * @author Victor Nazarov <asviraspossible@gmail.com>
 */

@GenerateValueClassForVisitor(resultVariableName = "R", valueClassName = "GADTBase")
interface GADTBaseVisitor<SI, SB, ST, R> {
    R _literal(int i);
    R _plus(SI a, SI b);
    R _isLessOrEqual(SI a, SI b);
    R _if_(SB condition, ST iftrue, ST iffalse);
}