Implemented translation of anonymous variables.

include/anthem/Context.h

@@ -22,6 +22,7 @@ struct Context
 		isChoiceRule = false;
 		numberOfHeadLiterals = 0;
 		auxiliaryBodyVariableID = 1;
+		anonymousVariableID = 1;
 	}
 
 	output::Logger logger;
@@ -30,6 +31,7 @@ struct Context
 	bool isChoiceRule = false;
 	size_t numberOfHeadLiterals = 0;
 	size_t auxiliaryBodyVariableID = 1;
+	size_t anonymousVariableID = 1;
 
 	bool simplify = false;
 };

include/anthem/Term.h

@@ -83,8 +83,16 @@ struct TermTranslateVisitor
 		return std::experimental::nullopt;
 	}
 
-	std::experimental::optional<ast::Term> visit(const Clingo::AST::Variable &variable, const Clingo::AST::Term &, Context &)
+	std::experimental::optional<ast::Term> visit(const Clingo::AST::Variable &variable, const Clingo::AST::Term &, Context &context)
 	{
+		if (strcmp(variable.name, "_") == 0)
+		{
+			std::string variableName = AnonymousVariablePrefix + std::to_string(context.anonymousVariableID);
+			context.anonymousVariableID++;
+
+			return ast::Term::make<ast::Variable>(std::move(variableName), ast::Variable::Type::Reserved);
+		}
+
 		return ast::Term::make<ast::Variable>(std::string(variable.name), ast::Variable::Type::UserDefined);
 	}
 

include/anthem/Utils.h

@@ -58,6 +58,7 @@ inline bool isPrefix(const char *prefix, const char *string)
 
 constexpr const auto AuxiliaryHeadVariablePrefix = "V";
 constexpr const auto AuxiliaryBodyVariablePrefix = "X";
+constexpr const auto AnonymousVariablePrefix = "A";
 constexpr const auto UserVariablePrefix = "_";
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -65,12 +66,14 @@ constexpr const auto UserVariablePrefix = "_";
 inline bool isReservedVariableName(const char *variableName)
 {
 	if (!isPrefix(AuxiliaryBodyVariablePrefix, variableName)
-	    && !isPrefix(AuxiliaryHeadVariablePrefix, variableName))
+	    && !isPrefix(AuxiliaryHeadVariablePrefix, variableName)
+	    && !isPrefix(AnonymousVariablePrefix, variableName))
 	{
 		return false;
 	}
 
 	assert(std::strlen(AuxiliaryBodyVariablePrefix) == std::strlen(AuxiliaryHeadVariablePrefix));
+	assert(std::strlen(AuxiliaryBodyVariablePrefix) == std::strlen(AnonymousVariablePrefix));
 
 	const auto prefixLength = std::strlen(AuxiliaryBodyVariablePrefix);
 

include/anthem/output/AST.h

@@ -216,6 +216,7 @@ inline output::ColorStream &operator<<(output::ColorStream &stream, const String
 inline output::ColorStream &operator<<(output::ColorStream &stream, const Variable &variable)
 {
 	assert(!variable.name.empty());
+	assert(variable.name != "_");
 
 	if (variable.type == ast::Variable::Type::Reserved || !isReservedVariableName(variable.name.c_str()))
 		return (stream << output::Variable(variable.name.c_str()));

tests/TestTranslation.cpp

@@ -69,10 +69,10 @@ TEST_CASE("[translation] Rules are translated correctly", "[translation]")
 
 	SECTION("escaping conflicting variable names")
 	{
-		input << "p(X1, V1) :- q(X1), q(V1).";
+		input << "p(X1, V1, A1) :- q(X1), q(V1), q(A1).";
 		anthem::translate("input", input, context);
 
-		REQUIRE(output.str() == "((V1 in _X1 and V2 in _V1 and exists X1 (X1 in _X1 and q(X1)) and exists X2 (X2 in _V1 and q(X2))) -> p(V1, V2))\n");
+		REQUIRE(output.str() == "((V1 in _X1 and V2 in _V1 and V3 in _A1 and exists X1 (X1 in _X1 and q(X1)) and exists X2 (X2 in _V1 and q(X2)) and exists X3 (X3 in _A1 and q(X3))) -> p(V1, V2, V3))\n");
 	}
 
 	SECTION("fact")
@@ -201,8 +201,8 @@ TEST_CASE("[translation] Rules are translated correctly", "[translation]")
 		input << "f; q(A1, A2); p(A3, r(A4)); g(g(A5)) :- g(A3), f, q(A4, A1), p(A2, A5).";
 		anthem::translate("input", input, context);
 
-		REQUIRE(output.str() == "((V1 in A1 and V2 in A2 and V3 in A3 and V4 in r(A4) and V5 in g(A5)"
+		REQUIRE(output.str() == "((V1 in _A1 and V2 in _A2 and V3 in _A3 and V4 in r(_A4) and V5 in g(_A5)"
-		        " and exists X1 (X1 in A3 and g(X1)) and f and exists X2, X3 (X2 in A4 and X3 in A1 and q(X2, X3)) and exists X4, X5 (X4 in A2 and X5 in A5 and p(X4, X5)))"
+		        " and exists X1 (X1 in _A3 and g(X1)) and f and exists X2, X3 (X2 in _A4 and X3 in _A1 and q(X2, X3)) and exists X4, X5 (X4 in _A2 and X5 in _A5 and p(X4, X5)))"
 		        " -> (q(V1, V2) or p(V3, V4) or g(V5) or f))\n");
 	}
 
@@ -261,4 +261,12 @@ TEST_CASE("[translation] Rules are translated correctly", "[translation]")
 
 		REQUIRE(output.str() == "((V1 in X and V2 in 1 and exists X1, X2 (X1 in X and X2 in 2 and not q(X1, X2)) and not p(V1, V2)) -> not p(V1, V2))\n((V1 in X and V2 in 1 and exists X1, X2 (X1 in X and X2 in 2 and not q(X1, X2)) and not s) -> not s)\n");
 	}
+
+	SECTION("anonymous variables")
+	{
+		input << "p(_, _) :- q(_, _).";
+		anthem::translate("input", input, context);
+
+		REQUIRE(output.str() == "((V1 in A1 and V2 in A2 and exists X1, X2 (X1 in A3 and X2 in A4 and q(X1, X2))) -> p(V1, V2))\n");
+	}
 }