A SWI-Prolog-like Json-Term converter for Prolog Cafe (Example Implementation)

gistfile1.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import jp.ac.kobe_u.cs.prolog.lang.DoubleTerm;
import jp.ac.kobe_u.cs.prolog.lang.IntegerTerm;
import jp.ac.kobe_u.cs.prolog.lang.ListTerm;
import jp.ac.kobe_u.cs.prolog.lang.Prolog;
import jp.ac.kobe_u.cs.prolog.lang.StructureTerm;
import jp.ac.kobe_u.cs.prolog.lang.SymbolTerm;
import jp.ac.kobe_u.cs.prolog.lang.Term;

/**
 * @author Masayuki Higashino
 */
public class JsonUtils {

	public static Term javaToProlog(Object o) throws IllegalArgumentException {
		if (o == null) {
			return new StructureTerm(SymbolTerm.makeSymbol("@", 1), new Term[] { SymbolTerm.makeSymbol("null") });
		} else if (o instanceof Boolean) {
			return new StructureTerm(SymbolTerm.makeSymbol("@", 1), new Term[] { SymbolTerm.makeSymbol(o.toString()) });
		} else if (o instanceof String) {
			return SymbolTerm.makeSymbol(o.toString());
		} else if (o instanceof Integer) {
			return new IntegerTerm((Integer) o);
		} else if (o instanceof Double) {
			return new DoubleTerm((Double) o);
		} else if (o instanceof List) {
			Term term = Prolog.Nil;
			List<?> list = (List<?>) o;
			ListIterator<?> i = list.listIterator(list.size());
			while (i.hasPrevious())
				term = new ListTerm(javaToProlog(i.previous()), term);
			return term;
		} else if (o instanceof Map) {
			SymbolTerm json = SymbolTerm.makeSymbol("json", 1);
			Term list = Prolog.Nil;
			for (Map.Entry<?, ?> entry : ((Map<?, ?>) o).entrySet()) {
				SymbolTerm key = SymbolTerm.makeSymbol(entry.getKey().toString());
				Term value = javaToProlog(entry.getValue());
				Term[] args = new Term[] { key, value };
				StructureTerm e = new StructureTerm(SymbolTerm.makeSymbol("=", 2), args);
				list = new ListTerm(e, list);
			}
			return new StructureTerm(json, new Term[] { list });
		} else {
			throw new IllegalArgumentException("expect to null|Boolean|String|Integer|Double|List|Map: " + o.toString());
		}
	}

	public static Object prologToJava(Term o) throws IllegalArgumentException {
		if (o.isSymbol()) {
			return ((SymbolTerm) o).name();
		} else if (o.isInteger()) {
			return ((IntegerTerm) o).intValue();
		} else if (o.isDouble()) {
			return ((DoubleTerm) o).doubleValue();
		} else if (o.isList()) {
			List<Object> list = new ArrayList<>();
			Term l = o;
			while (!l.isNil()) {
				Term e = ((ListTerm) l).car();
				list.add(prologToJava(e));
				l = ((ListTerm) l).cdr();
			}
			return list;
		} else if (o.isStructure()) {
			StructureTerm t = (StructureTerm) o;
			if (t.name().equals("@") && t.arity() == 1 && t.args()[0].isSymbol()) {
				String value = ((SymbolTerm) t.args()[0]).name();
				if (value.equals("true")) {
					return true;
				} else if (value.equals("false")) {
					return false;
				} else if (value.equals("null")) {
					return null;
				} else {
					throw new IllegalArgumentException("expect to true|false|null: " + o.toString());
				}
			} else if (t.name().equals("json") && t.arity() == 1 && t.args()[0].isList()) {
				Map<Object, Object> map = new HashMap<>();
				Term l = t.args()[0];
				while (!l.isNil()) {
					Term e = ((ListTerm) l).car();
					if (e.isStructure()) {
						StructureTerm entry = (StructureTerm) e;
						if (entry.name().equals("=") && entry.arity() == 2) {
							Term k = entry.args()[0];
							Term v = entry.args()[1];
							map.put(prologToJava(k), prologToJava(v));
						} else {
							throw new IllegalArgumentException("expect to =/2: " + o.toString());
						}
					} else {
						throw new IllegalArgumentException("expect to =/2: " + o.toString());
					}
					l = ((ListTerm) l).cdr();
				}
				return map;
			} else {
				throw new IllegalArgumentException("expect to @/1|json/1: " + o.toString());
			}
		} else {
			throw new IllegalArgumentException("expect to symbol|integer|double|list|structure: " + o.toString());
		}
	}

	public static void main(String[] args) throws Exception {
		Map<String, Object> java1 = new HashMap<String, Object>() {
			private static final long serialVersionUID = 1L;
			{
				put("jsonrpc", "2.0");
				put("method", "user.create");
				put("params", new HashMap<String, Object>() {
					private static final long serialVersionUID = 1L;
					{
						put("email", "user@example.net");
						put("password", "drowssap");
						put("contents", Arrays.asList("aa", "bb", true, null, false));
					}
				});
				put("id", "12345");
			}
		};
		Term prolog = javaToProlog(java1);
		Object java2 = prologToJava(prolog);
		System.err.println(java1);
		System.err.println(prolog);
		System.err.println(java2);
	}

}