Implementation of Limit operator

src/qir/ast/operator/QIRLimit.java

+package qir.ast.operator;
+
+import com.oracle.truffle.api.source.SourceSection;
+
+import qir.ast.QIRNode;
+import qir.util.IQIRVisitor;
+
+/**
+ * The {@link QIRLimit} represents the operation that limits the number of results.
+ */
+public final class QIRLimit extends QIROperator {
+    /**
+     * The limit for the number of results.
+     */
+    private final QIRNode limit;
+    /**
+     * The next {@link QIROperator} in the tree.
+     */
+    private final QIRNode child;
+
+    public QIRLimit(final SourceSection source, final QIRNode limit, final QIRNode child) {
+        super(source);
+        this.limit = limit;
+        this.child = child;
+    }
+
+    public final QIRNode getLimit() {
+        return limit;
+    }
+
+    public final QIRNode getChild() {
+        return child;
+    }
+
+    @Override
+    public final <T> T accept(final IQIRVisitor<T> visitor) {
+        return visitor.visit(this);
+    }
+}
\ No newline at end of file

src/qir/driver/QIRSQLVisitor.java

@@ -26,98 +26,126 @@ public class QIRSQLVisitor implements IQIRVisitor<String> {
         return res;
     }
 
+    @Override
     public final String visit(final QIRProject qirProject) {
         return "select " + qirProject.getFormatter().accept(this) + " " + qirProject.getChild().accept(this);
     }
 
+    @Override
     public final String visit(final QIRScan qirScan) {
         return "from " + qirScan.getTable().accept(this);
     }
 
+    @Override
     public final String visit(final QIRSelect qirSelect) {
         return qirSelect.getChild().accept(this) + " where " + qirSelect.getFilter().accept(this);
     }
 
     // TODO: Do something with "eq" attribute of QIRGroup.
+    @Override
     public final String visit(final QIRGroup qirGroup) {
         return qirGroup.getChild().accept(this) + " group by " + qirGroup.getGroup().accept(this);
     }
 
+    @Override
     public final String visit(final QIROrder qirOrder) {
         return qirOrder.getChild().accept(this) + " order by " + qirOrder.getOrder().accept(this);
     }
 
     // TODO: Do something with "filter" attribute of QIRJoin.
+    @Override
     public final String visit(final QIRJoin qirJoin) {
         final String right = qirJoin.getRight().accept(this);
 
         return qirJoin.getLeft().accept(this) + " natural join " + (right.substring(0, 5).equals("from ") ? right.substring(5) : right);
     }
 
+    @Override
+    public final String visit(final QIRLimit qirLimit) {
+        return qirLimit.getChild().accept(this) + " limit " + qirLimit.getLimit().accept(this);
+    }
+
+    @Override
     public final String visit(final QIRLambda qirLambda) {
         return qirLambda.getBody().accept(this);
     }
 
+    @Override
     public final String visit(final QIRApply qirApply) {
         return qirApply.getLeft().accept(this) + "(" + qirApply.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRPlus qirPlus) {
         return "(" + qirPlus.getLeft().accept(this) + ") + (" + qirPlus.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRMinus qirMinus) {
         return "(" + qirMinus.getLeft().accept(this) + ") - (" + qirMinus.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRStar qirStar) {
         return "(" + qirStar.getLeft().accept(this) + ") * (" + qirStar.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRDiv qirDiv) {
         return "(" + qirDiv.getLeft().accept(this) + ") / (" + qirDiv.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRMod qirMod) {
         return "(" + qirMod.getLeft().accept(this) + ") / (" + qirMod.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRAnd qirAnd) {
         return "(" + qirAnd.getLeft().accept(this) + ") AND (" + qirAnd.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIROr qirOr) {
         return "(" + qirOr.getLeft().accept(this) + ") OR (" + qirOr.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIREqual qirEqual) {
         return "(" + qirEqual.getLeft().accept(this) + ") = (" + qirEqual.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRGreaterOrEqual qirGreaterOrEqual) {
         return "(" + qirGreaterOrEqual.getLeft().accept(this) + ") >= (" + qirGreaterOrEqual.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRGreaterThan qirGreaterThan) {
         return "(" + qirGreaterThan.getLeft().accept(this) + ") > (" + qirGreaterThan.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRLowerOrEqual qirLowerOrEqual) {
         return "(" + qirLowerOrEqual.getLeft().accept(this) + ") <= (" + qirLowerOrEqual.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRLowerThan qirLowerThan) {
         return "(" + qirLowerThan.getLeft().accept(this) + ") < (" + qirLowerThan.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRNotEqual qirNotEqual) {
         return "(" + qirNotEqual.getLeft().accept(this) + ") != (" + qirNotEqual.getRight().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRNot qirNot) {
         return "NOT (" + qirNot.getChild().accept(this) + ")";
     }
 
+    @Override
     public final String visit(final QIRTable qirTable) {
         return qirTable.getTableName();
     }
@@ -125,10 +153,12 @@ public class QIRSQLVisitor implements IQIRVisitor<String> {
     /**
      * @param qirLnil Unique instance of the empty list in QIR.
      */
+    @Override
     public final String visit(final QIRLnil qirLnil) {
         return "";
     }
 
+    @Override
     public final String visit(final QIRLcons qirLcons) {
         final String value = qirLcons.getValue().accept(this);
         final String tail = qirLcons.getTail().accept(this);
@@ -141,6 +171,7 @@ public class QIRSQLVisitor implements IQIRVisitor<String> {
     /**
      * @param qirLdestr Unsupported feature.
      */
+    @Override
     public final String visit(final QIRLdestr qirLdestr) {
         throw new UnsupportedOperationException(this.getClass().getSimpleName() + " error: unsupported node.");
     }
@@ -148,10 +179,12 @@ public class QIRSQLVisitor implements IQIRVisitor<String> {
     /**
      * @param qirTnil Unique instance of the empty tuple in QIR.
      */
+    @Override
     public final String visit(final QIRTnil qirTnil) {
         return "";
     }
 
+    @Override
     public final String visit(final QIRTcons qirTcons) {
         final String id = qirTcons.getId();
         String value = qirTcons.getValue().accept(this);
@@ -163,26 +196,32 @@ public class QIRSQLVisitor implements IQIRVisitor<String> {
         return value + ", " + tail;
     }
 
+    @Override
     public final String visit(final QIRTdestr qirTdestr) {
         return qirTdestr.getColName();
     }
 
+    @Override
     public final String visit(final QIRString qirString) {
         return "'" + qirString.getValue() + "'";
     }
 
+    @Override
     public final String visit(final QIRNumber qirNumber) {
         return Long.toString(qirNumber.getValue());
     }
 
+    @Override
     public final String visit(final QIRBigNumber qirBigNumber) {
         return qirBigNumber.getValue().toString();
     }
 
+    @Override
     public final String visit(final QIRBoolean qirBoolean) {
         return qirBoolean.getValue() ? "true" : "false";
     }
 
+    @Override
     public final String visit(final QIRTruffleNode qirTruffleNode) {
         final String funName = qirTruffleNode.getName();
         prolog.put(funName, qirTruffleNode.getCode());

src/qir/reduction/QIRGreedyReduceVisitor.java

@@ -49,6 +49,11 @@ public final class QIRGreedyReduceVisitor implements IQIRVisitor<QIRNode> {
         return new QIRJoin(qirJoin.getSourceSection(), qirJoin.getFilter().accept(this), qirJoin.getLeft().accept(this), qirJoin.getRight().accept(this));
     }
 
+    @Override
+    public final QIRNode visit(final QIRLimit qirLimit) {
+        return new QIRLimit(qirLimit.getSourceSection(), qirLimit.getLimit().accept(this), qirLimit.getChild().accept(this));
+    }
+
     @Override
     public final QIRNode visit(final QIRLambda qirLambda) {
         return new QIRLambda(qirLambda.getSourceSection(), qirLambda.getName(), qirLambda.getVar(), qirLambda.getBody().accept(this));

src/qir/util/IQIRVisitor.java

@@ -25,6 +25,8 @@ public interface IQIRVisitor<T> {
 
     public abstract T visit(final QIRJoin qirJoin);
 
+    public abstract T visit(final QIRLimit qirLimit);
+
     public default T visit(final QIROperator qirOperator) {
         throw new UnsupportedOperationException("Error: unsupported operator " + qirOperator.getClass().getSimpleName() + ".");
     }

src/qir/util/QIRFreeVarsVisitor.java

@@ -54,6 +54,12 @@ public final class QIRFreeVarsVisitor implements IQIRVisitor<HashMap<String, QIR
         return qirJoin.getRight().accept(this);
     }
 
+    @Override
+    public final HashMap<String, QIRVariable> visit(final QIRLimit qirLimit) {
+        qirLimit.getLimit().accept(this);
+        return qirLimit.getChild().accept(this);
+    }
+
     @Override
     public final HashMap<String, QIRVariable> visit(final QIRLambda qirLambda) {
         final QIRVariable var = qirLambda.getVar();

src/qir/util/QIRPrintVisitor.java

@@ -39,6 +39,11 @@ public final class QIRPrintVisitor implements IQIRVisitor<String> {
         return "Join(" + qirJoin.getFilter().accept(this) + ", " + qirJoin.getLeft().accept(this) + ", " + qirJoin.getRight().accept(this) + ")";
     }
 
+    @Override
+    public final String visit(final QIRLimit qirLimit) {
+        return "Limit(" + qirLimit.getLimit().accept(this) + ", " + qirLimit.getChild().accept(this) + ")";
+    }
+
     @Override
     public final String visit(final QIRLambda qirLambda) {
         return "(function:" + qirLambda.getName() + " " + ((qirLambda.getVar() != null) ? qirLambda.getVar().getId() : "<none>") + " -> " + qirLambda.getBody().accept(this) + ")";