Added DISTINCT clause as an iterator

pkg/compiler/visitor.go

@@ -192,6 +192,7 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 
 	var spread bool
 	var distinct bool
+	var distinctSrc core.SourceMap
 	forRetCtx := ctx.ForExpressionReturn().(*fql.ForExpressionReturnContext)
 	returnCtx := forRetCtx.ReturnExpression()
 
@@ -203,7 +204,13 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 			return nil, err
 		}
 
-		distinct = returnCtx.Distinct() != nil
+		distinctCtx := returnCtx.Distinct()
+
+		if distinctCtx != nil {
+			distinct = true
+			token := distinctCtx.GetSymbol()
+			distinctSrc = core.NewSourceMap(token.GetText(), token.GetLine(), token.GetColumn())
+		}
 
 		predicate.Add(returnExp)
 	} else {
@@ -225,7 +232,6 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 		keyVarName,
 		src,
 		predicate,
-		distinct,
 		spread,
 	)
 
@@ -233,6 +239,10 @@ func (v *visitor) doVisitForExpression(ctx *fql.ForExpressionContext, scope *sco
 		return nil, err
 	}
 
+	if distinct {
+		forExp.AddDistinct(distinctSrc)
+	}
+
 	for _, clause := range ctx.AllForExpressionClause() {
 		clause := clause.(*fql.ForExpressionClauseContext)
 

pkg/runtime/expressions/clauses/distinct.go

@@ -0,0 +1,28 @@
+package clauses
+
+import (
+	"context"
+	"github.com/MontFerret/ferret/pkg/runtime/collections"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+)
+
+type DistinctClause struct {
+	*baseClause
+}
+
+func NewDistinctClause(
+	src core.SourceMap,
+	dataSource collections.IterableExpression,
+) *DistinctClause {
+	return &DistinctClause{&baseClause{src, dataSource}}
+}
+
+func (clause *DistinctClause) Iterate(ctx context.Context, scope *core.Scope) (collections.Iterator, error) {
+	src, err := clause.dataSource.Iterate(ctx, scope)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return collections.NewUniqueIterator(src)
+}

pkg/runtime/expressions/for.go

@@ -15,7 +15,6 @@ type ForExpression struct {
 	keyVar     string
 	dataSource collections.IterableExpression
 	predicate  core.Expression
-	distinct   bool
 	spread     bool
 }
 
@@ -25,7 +24,6 @@ func NewForExpression(
 	keyVar string,
 	dataSource collections.IterableExpression,
 	predicate core.Expression,
-	distinct bool,
 	spread bool,
 ) (*ForExpression, error) {
 	if valVar == "" {
@@ -45,7 +43,6 @@ func NewForExpression(
 		valVar, keyVar,
 		dataSource,
 		predicate,
-		distinct,
 		spread,
 	}, nil
 }
@@ -62,6 +59,10 @@ func (e *ForExpression) AddSort(src core.SourceMap, sorters ...*clauses.SorterEx
 	e.dataSource = clauses.NewSortClause(src, e.dataSource, e.valVar, sorters...)
 }
 
+func (e *ForExpression) AddDistinct(src core.SourceMap) {
+	e.dataSource = clauses.NewDistinctClause(src, e.dataSource)
+}
+
 func (e *ForExpression) Exec(ctx context.Context, scope *core.Scope) (core.Value, error) {
 	iterator, err := e.dataSource.Iterate(ctx, scope)
 
@@ -69,13 +70,6 @@ func (e *ForExpression) Exec(ctx context.Context, scope *core.Scope) (core.Value
 		return values.None, err
 	}
 
-	// Hash map for a check for uniqueness
-	var hashes map[uint64]bool
-
-	if e.distinct {
-		hashes = make(map[uint64]bool)
-	}
-
 	res := values.NewArray(10)
 
 	for iterator.HasNext() {
@@ -98,28 +92,14 @@ func (e *ForExpression) Exec(ctx context.Context, scope *core.Scope) (core.Value
 			return values.None, err
 		}
 
-		var el core.Value
-
-		// The result shouldn't be distinct
-		// Just add the output
-		if !e.distinct {
-			el = out
-		} else {
-			// We need to check whether the value already exists in the result set
-			hash := out.Hash()
-			_, exists := hashes[hash]
-
-			if !exists {
-				hashes[hash] = true
-				el = out
-			}
-		}
-
-		if el != nil {
 		if !e.spread {
-				res.Push(el)
+			res.Push(out)
 		} else {
-				elements := el.(*values.Array)
+			elements, ok := out.(*values.Array)
+
+			if !ok {
+				return values.None, core.Error(core.ErrInvalidOperation, "spread of non-array value")
+			}
 
 			elements.ForEach(func(i core.Value, _ int) bool {
 				res.Push(i)
@@ -128,7 +108,6 @@ func (e *ForExpression) Exec(ctx context.Context, scope *core.Scope) (core.Value
 			})
 		}
 	}
-	}
 
 	return res, nil
 }