Implement RTTI for the Java-backend (incomplete)

Estimated hours taken: 30
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Implement RTTI for the Java-backend (incomplete)

java/runtime/PseudoTypeInfo.java:
java/runtime/TypeCtorInfo_Struct.java:
java/runtime/TypeInfo_Struct.java:
	Implement the `unify' operation for these classes.  This implementation
	actually just compares them.

library/rtti_implementation.m:
	Document a bug in notag_functor_arg_type/1

	Define the foreign type of `type_layout' as `TypeLayout' in Java.

	Correct an off-by-one error in type_ctor_and_args/3.

	Implement deconstruct/8 for TypeCtorRep = enum.

	Implement the following predicates in Java:
		get_var_arity_typeinfo_arity/1
		get_pti_from_arg_types/2
		typeinfo_is_variable/2
		get_type_ctor_info/1
		get_primary_tag/1
		get_remote_secondary_tag/1
		ptag_index/2
		sectag_locn/1
		du_sectag_alternatives/2
		type_info_index/2
		type_ctor_arity/1
		type_ctor_rep/1
		type_ctor_module_name/1
		type_ctor_name/1
		type_ctor_functors/1
		type_layout/1
		unsafe_cast/1
		du_functor_desc/3
		du_functor_name/1
		du_functor_arity/1
		du_functor_arg_type_contains_var/1
		du_functor_sectag_locn/1
		du_functor_primary/1
		du_functor_secondary/1
		du_functor_ordinal/1
		du_functor_arg_types/1
		du_functor_arg_names/1
		du_functor_exist_info/1
		enum_functor_desc/3
		enum_functor_name/1
		enum_functor_ordinal/1
		notag_functor_desc/3
		notag_functor_name/1
		notag_functor_arg_type/1
		notag_functor_arg_name/1
		null/1
		null_string/0
		unsafe_get_enum_value/1

library/type_desc.m:
	Implement the following procedures for Java:
		type_of/1
		has_type/1
		type_ctor_and_args/3
		type_ctor_name_and_arity/4

	Implement the Java classes `type_desc_0' and `type_ctor_desc_0'.

java/runtime/PseudoTypeInfo.java

@@ -25,4 +25,14 @@ public class PseudoTypeInfo {
 	public int variable_number;
 	public    PseudoTypeInfo(int n) { variable_number = n; }
 	protected PseudoTypeInfo()      { variable_number = -1; }
+
+		// XXX This should be renamed `equals'
+	public boolean unify(PseudoTypeInfo ti) {
+		if (this.getClass() == TypeInfo_Struct.class &&
+				ti.getClass() == TypeInfo_Struct.class) {
+			return ((TypeInfo_Struct) this).unify(
+						(TypeInfo_Struct) ti);
+		}
+		return variable_number == ti.variable_number;
+	}
 }

java/runtime/TypeCtorInfo_Struct.java

@@ -48,4 +48,14 @@ public class TypeCtorInfo_Struct extends PseudoTypeInfo {
 			value_ordered_functor_descs;
 		type_ctor_flags = flags;
 	}
+
+		// XXX this should be renamed `equals'
+	public boolean unify(TypeCtorInfo_Struct tci) {
+		return this == tci;
+		/*
+		return type_ctor_module_name.equals(tci.type_ctor_module_name)
+				&& type_ctor_name.equals(tci.type_ctor_name)
+				&& arity == tci.arity;
+		*/
+	}
 }

java/runtime/TypeInfo_Struct.java

@@ -125,4 +125,32 @@ public class TypeInfo_Struct extends PseudoTypeInfo {
 			}
 		}
 	}
+
+		// XXX this should be renamed `equals'
+	public boolean unify(TypeInfo_Struct ti) {
+		if (this == ti) {
+			return true;
+		}
+
+		if (type_ctor.unify(ti.type_ctor) == false) {
+			return false;
+		}
+
+		if (args == null || ti.args == null) {
+			if (args == null && ti.args == null) {
+				return true;
+			}
+			return false;
+		}
+
+		for (int i = 0; i < args.length || i < ti.args.length; i++) {
+			if (i == args.length || i == ti.args.length) {
+				return false;
+			}
+			if (args[i].unify(ti.args[i]) == false) {
+				return false;
+			}
+		}
+		return true;
+	}
 }