[MOREL-204] Add take and skip relational operators

Now that `take` is a keyword, quote uses of `List.take` function
in standard basis library.

Push skip and take to Calcite.

Fix pushing yield into Calcite (it only worked if it was the last step).

Remove call to RelJson constructor deprecated in Calcite 1.36

Fixes #204

docs/reference.md

@@ -38,7 +38,7 @@ Contributions are welcome!
 
 In Morel but not Standard ML:
 * `from` expression with `in`, `suchthat`, `join`, `where`, `group`,
-  `compute`, `order`, `yield` clauses
+  `compute`, `order`, `skip`, `take`, `yield` clauses
 * `union`, `except`, `intersect`, `elem`, `notelem` operators
 * "*lab* `=`" is optional in `exprow`
 * identifiers may be quoted
@@ -159,7 +159,9 @@ In Standard ML but not in Morel:
                                 compute clause (<i>a</i> &gt; 1)
     | <b>order</b> <i>orderItem<sub>1</sub></i> <b>,</b> ... <b>,</b> <i>orderItem<sub>o</sub></i>
                                 order clause (<i>o</i> &ge; 1)
-    | <b>yield</b> <i>exp</i>
+    | <b>skip</b> <i>exp</i>                  skip clause
+    | <b>take</b> <i>exp</i>                  take clause
+    | <b>yield</b> <i>exp</i>                 yield clause
 <i>groupKey</i> &rarr; [ <i>id</i> <b>=</b> ] <i>exp</i>
 <i>agg</i> &rarr; [ <i>id</i> <b>=</b> ] <i>exp</i> [ <b>of</b> <i>exp</i> ]
 <i>orderItem</i> &rarr; <i>exp</i> [ <b>desc</b> ]

src/main/java/net/hydromatic/morel/ast/Ast.java

@@ -1707,6 +1707,58 @@ public Where copy(Exp exp) {
     }
   }
 
+  /** A {@code skip} clause in a {@code from} expression. */
+  public static class Skip extends FromStep {
+    public final Exp exp;
+
+    Skip(Pos pos, Exp exp) {
+      super(pos, Op.SKIP);
+      this.exp = exp;
+    }
+
+    @Override AstWriter unparse(AstWriter w, int left, int right) {
+      return w.append(" skip ").append(exp, 0, 0);
+    }
+
+    @Override public AstNode accept(Shuttle shuttle) {
+      return shuttle.visit(this);
+    }
+
+    @Override public void accept(Visitor visitor) {
+      visitor.visit(this);
+    }
+
+    public Skip copy(Exp exp) {
+      return this.exp.equals(exp) ? this : new Skip(pos, exp);
+    }
+  }
+
+  /** A {@code take} clause in a {@code from} expression. */
+  public static class Take extends FromStep {
+    public final Exp exp;
+
+    Take(Pos pos, Exp exp) {
+      super(pos, Op.TAKE);
+      this.exp = exp;
+    }
+
+    @Override AstWriter unparse(AstWriter w, int left, int right) {
+      return w.append(" take ").append(exp, 0, 0);
+    }
+
+    @Override public AstNode accept(Shuttle shuttle) {
+      return shuttle.visit(this);
+    }
+
+    @Override public void accept(Visitor visitor) {
+      visitor.visit(this);
+    }
+
+    public Take copy(Exp exp) {
+      return this.exp.equals(exp) ? this : new Take(pos, exp);
+    }
+  }
+
   /** A {@code yield} clause in a {@code from} expression. */
   public static class Yield extends FromStep {
     public final Exp exp;

src/main/java/net/hydromatic/morel/ast/AstBuilder.java

@@ -483,6 +483,14 @@ public Ast.FromStep where(Pos pos, Ast.Exp exp) {
     return new Ast.Where(pos, exp);
   }
 
+  public Ast.FromStep skip(Pos pos, Ast.Exp exp) {
+    return new Ast.Skip(pos, exp);
+  }
+
+  public Ast.FromStep take(Pos pos, Ast.Exp exp) {
+    return new Ast.Take(pos, exp);
+  }
+
   public Ast.FromStep yield(Pos pos, Ast.Exp exp) {
     return new Ast.Yield(pos, exp);
   }

src/main/java/net/hydromatic/morel/ast/Core.java

@@ -1238,6 +1238,66 @@ public Where copy(Exp exp, List<Binding> bindings) {
     }
   }
 
+  /** A {@code skip} clause in a {@code from} expression. */
+  public static class Skip extends FromStep {
+    public final Exp exp;
+
+    Skip(ImmutableList<Binding> bindings, Exp exp) {
+      super(Op.SKIP, bindings);
+      this.exp = requireNonNull(exp, "exp");
+    }
+
+    @Override public Skip accept(Shuttle shuttle) {
+      return shuttle.visit(this);
+    }
+
+    @Override public void accept(Visitor visitor) {
+      visitor.visit(this);
+    }
+
+    @Override protected AstWriter unparse(AstWriter w, From from, int ordinal,
+        int left, int right) {
+      return w.append(" skip ").append(exp, 0, 0);
+    }
+
+    public Skip copy(Exp exp, List<Binding> bindings) {
+      return exp == this.exp
+          && bindings.equals(this.bindings)
+          ? this
+          : core.skip(bindings, exp);
+    }
+  }
+
+  /** A {@code take} clause in a {@code from} expression. */
+  public static class Take extends FromStep {
+    public final Exp exp;
+
+    Take(ImmutableList<Binding> bindings, Exp exp) {
+      super(Op.TAKE, bindings);
+      this.exp = requireNonNull(exp, "exp");
+    }
+
+    @Override public Take accept(Shuttle shuttle) {
+      return shuttle.visit(this);
+    }
+
+    @Override public void accept(Visitor visitor) {
+      visitor.visit(this);
+    }
+
+    @Override protected AstWriter unparse(AstWriter w, From from, int ordinal,
+        int left, int right) {
+      return w.append(" take ").append(exp, 0, 0);
+    }
+
+    public Take copy(Exp exp, List<Binding> bindings) {
+      return exp == this.exp
+          && bindings.equals(this.bindings)
+          ? this
+          : core.take(bindings, exp);
+    }
+  }
+
   /** An {@code order} clause in a {@code from} expression. */
   public static class Order extends FromStep {
     public final ImmutableList<OrderItem> orderItems;

src/main/java/net/hydromatic/morel/ast/CoreBuilder.java

@@ -521,6 +521,14 @@ public Core.Where where(List<Binding> bindings, Core.Exp exp) {
     return new Core.Where(ImmutableList.copyOf(bindings), exp);
   }
 
+  public Core.Skip skip(List<Binding> bindings, Core.Exp exp) {
+    return new Core.Skip(ImmutableList.copyOf(bindings), exp);
+  }
+
+  public Core.Take take(List<Binding> bindings, Core.Exp exp) {
+    return new Core.Take(ImmutableList.copyOf(bindings), exp);
+  }
+
   public Core.Yield yield_(List<Binding> bindings, Core.Exp exp) {
     return new Core.Yield(ImmutableList.copyOf(bindings), exp);
   }

src/main/java/net/hydromatic/morel/ast/FromBuilder.java

@@ -29,6 +29,7 @@
 import org.apache.calcite.util.Util;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
+import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -192,6 +193,19 @@ public FromBuilder where(Core.Exp condition) {
     return addStep(core.where(bindings, condition));
   }
 
+  public FromBuilder skip(Core.Exp count) {
+    if (count.op == Op.INT_LITERAL
+        && ((Core.Literal) count).value.equals(BigDecimal.ZERO)) {
+      // skip "skip 0"
+      return this;
+    }
+    return addStep(core.skip(bindings, count));
+  }
+
+  public FromBuilder take(Core.Exp count) {
+    return addStep(core.take(bindings, count));
+  }
+
   public FromBuilder group(SortedMap<Core.IdPat, Core.Exp> groupExps,
       SortedMap<Core.IdPat, Core.Aggregate> aggregates) {
     return addStep(core.group(groupExps, aggregates));
@@ -378,6 +392,14 @@ private class StepHandler extends Visitor {
       where(where.exp);
     }
 
+    @Override protected void visit(Core.Skip skip) {
+      skip(skip.exp);
+    }
+
+    @Override protected void visit(Core.Take take) {
+      take(take.exp);
+    }
+
     @Override protected void visit(Core.Yield yield) {
       yield_(false, yield.bindings, yield.exp);
     }

src/main/java/net/hydromatic/morel/ast/Op.java

@@ -137,6 +137,8 @@ public enum Op {
   COMPUTE,
   ORDER,
   ORDER_ITEM,
+  SKIP,
+  TAKE,
   YIELD,
   AGGREGATE,
   IF;

src/main/java/net/hydromatic/morel/ast/Shuttle.java

@@ -240,6 +240,14 @@ protected AstNode visit(Ast.Where where) {
     return ast.where(where.pos, where.exp.accept(this));
   }
 
+  protected AstNode visit(Ast.Skip skip) {
+    return ast.skip(skip.pos, skip.exp.accept(this));
+  }
+
+  protected AstNode visit(Ast.Take take) {
+    return ast.take(take.pos, take.exp.accept(this));
+  }
+
   protected AstNode visit(Ast.Yield yield) {
     return ast.yield(yield.pos, yield.exp.accept(this));
   }
@@ -395,6 +403,14 @@ protected Core.Where visit(Core.Where where) {
     return where.copy(where.exp.accept(this), where.bindings);
   }
 
+  protected Core.Skip visit(Core.Skip skip) {
+    return skip.copy(skip.exp.accept(this), skip.bindings);
+  }
+
+  protected Core.Take visit(Core.Take take) {
+    return take.copy(take.exp.accept(this), take.bindings);
+  }
+
   protected Core.Group visit(Core.Group group) {
     return group.copy(visitSortedMap(group.groupExps),
         visitSortedMap(group.aggregates));

src/main/java/net/hydromatic/morel/ast/Visitor.java

@@ -206,6 +206,14 @@ protected void visit(Ast.Where where) {
     where.exp.accept(this);
   }
 
+  protected void visit(Ast.Skip skip) {
+    skip.exp.accept(this);
+  }
+
+  protected void visit(Ast.Take take) {
+    take.exp.accept(this);
+  }
+
   protected void visit(Ast.Yield yield) {
     yield.exp.accept(this);
   }
@@ -326,6 +334,14 @@ protected void visit(Core.Where where) {
     where.exp.accept(this);
   }
 
+  protected void visit(Core.Skip skip) {
+    skip.exp.accept(this);
+  }
+
+  protected void visit(Core.Take take) {
+    take.exp.accept(this);
+  }
+
   protected void visit(Core.NonRecValDecl valDecl) {
     valDecl.pat.accept(this);
     valDecl.exp.accept(this);