iter-ops raised above assign; 'cat' operator returns an iterator; $$ operator supports iterators producing a list of items

kern/iterator.go

@@ -7,6 +7,7 @@ package kern
 import (
 	// "errors"
 	"fmt"
+	"slices"
 )
 
 // Operator names
@@ -50,3 +51,45 @@ func IsIterator(v any) (ok bool) {
 	_, ok = v.(Iterator)
 	return
 }
+
+type IteratorBase struct {
+	ItemIndex int64
+	ItemCount int64
+	current   any
+}
+
+func (it *IteratorBase) Current() (item any, err error) {
+	return it.current, nil
+}
+
+func (it *IteratorBase) Index() int64 {
+	return it.ItemIndex
+}
+
+func (it *IteratorBase) Count() int64 {
+	return it.ItemCount
+}
+
+func (it *IteratorBase) HasOperation(name string) bool {
+	return slices.Contains([]string{NextName, IndexName, CountName, CurrentName}, name)
+}
+
+func (it *IteratorBase) Clean() (err error) {
+	return
+}
+
+func (it *IteratorBase) Reset() (err error) {
+	it.ItemIndex = -1
+	it.ItemCount = 0
+	it.current = nil
+	return
+}
+
+func (it *IteratorBase) Increment() {
+	it.ItemIndex++
+	it.ItemCount++
+}
+
+func (it *IteratorBase) SetCurrent(v any) {
+	it.current = v
+}

operator-cat.go

@@ -27,7 +27,7 @@ func newCatTerm(tk *scan.Token) (inst *scan.Term) {
 func evalCat(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var leftValue, rightValue any
 	var itLeft, itRight kern.Iterator
-	var item any
+	// var item any
 	var ok bool
 
 	if err = opTerm.CheckOperands(); err != nil {
@@ -54,16 +54,94 @@ func evalCat(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 		}
 	}
 
-	values := kern.NewListA()
-	for _, it := range []kern.Iterator{itLeft, itRight} {
-		for item, err = it.Next(); err == nil; item, err = it.Next() {
-			values.AppendItem(item)
+	// values := kern.NewListA()
+	// for _, it := range []kern.Iterator{itLeft, itRight} {
+	// 	for item, err = it.Next(); err == nil; item, err = it.Next() {
+	// 		values.AppendItem(item)
+	// 	}
+	// }
+	// if err == io.EOF {
+	// 	err = nil
+	// }
+	// v = values
+	v = newCatIterator(itLeft, itRight)
+	return
+}
+
+const catIteratorType = "cat"
+
+type catIterator struct {
+	kern.IteratorBase
+	itLeft    kern.Iterator
+	itRight   kern.Iterator
+	itCurrent kern.Iterator
+}
+
+func newCatIterator(itLeft, itRight kern.Iterator) (it *catIterator) {
+	it = &catIterator{
+		IteratorBase: kern.IteratorBase{},
+		itLeft:       itLeft,
+		itRight:      itRight,
+		itCurrent:    itLeft,
+	}
+	it.Reset()
+	return
+}
+
+func (it *catIterator) TypeName() string {
+	return catIteratorType
+}
+
+func (it *catIterator) String() string {
+	return fmt.Sprintf("$(%s %s %s)", it.itLeft, catIteratorType, it.itRight)
+}
+
+func (it *catIterator) Next() (item any, err error) {
+	if it.itCurrent == nil {
+		err = io.EOF
+	} else {
+		if item, err = it.itCurrent.Next(); err == nil {
+			it.Increment()
+		} else if err == io.EOF {
+			if it.itCurrent == it.itLeft {
+				it.itCurrent = it.itRight
+			} else {
+				return
+			}
+			if item, err = it.itCurrent.Next(); err == nil {
+				it.Increment()
+			} else {
+				it.itCurrent = nil
 			}
 		}
-	if err == io.EOF {
-		err = nil
 	}
-	v = values
+	it.SetCurrent(item)
+	return
+}
+
+// func (it *catIterator) Reset() (err error) {
+// 	err = it.itLeft.Reset()
+// 	it.IteratorBase.Reset()
+// 	return
+// }
+
+func (it *catIterator) CallOperation(name string, args map[string]any) (v any, err error) {
+	switch name {
+	case kern.NextName:
+		v, err = it.Next()
+	// case kern.ResetName:
+	// 	err = it.Reset()
+	// case kern.CleanName:
+	// 	err = it.Clean()
+	case kern.IndexName:
+		v = it.Index()
+	case kern.CurrentName:
+		v, err = it.Current()
+	case kern.CountName:
+		v = it.Count()
+	default:
+		err = kern.ErrNoOperation(name)
+	}
 	return
 }
 

operator-context.go

@@ -5,6 +5,8 @@
 package expr
 
 import (
+	"io"
+
 	"git.portale-stac.it/go-pkg/expr/kern"
 	"git.portale-stac.it/go-pkg/expr/scan"
 )
@@ -23,8 +25,8 @@ func newContextTerm(tk *scan.Token) (inst *scan.Term) {
 
 func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
 	var childValue any
-
 	var sourceCtx kern.ExprContext
+
 	if len(opTerm.Children) == 0 {
 		sourceCtx = ctx
 	} else if opTerm.Children[0].Symbol() == scan.SymVariable && opTerm.Children[0].Source() == "global" {
@@ -53,6 +55,20 @@ func evalContextValue(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error
 			}
 			v = d
 		}
+	} else if childValue != nil {
+		if it, ok := childValue.(kern.Iterator); ok {
+			var item any
+			values := kern.NewListA()
+			for item, err = it.Next(); err == nil; item, err = it.Next() {
+				values.AppendItem(item)
+			}
+			if err == io.EOF {
+				err = nil
+				v = values
+			}
+		} else {
+			err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
+		}
 	} else {
 		err = opTerm.ErrIncompatiblePrefixPostfixType(childValue)
 	}

scan/symbol-map.go

@@ -138,6 +138,7 @@ func init() {
 		SymKwMap:     {"map", SymClassOperator, PosInfix},
 		SymKwFilter:  {"filter", SymClassOperator, PosInfix},
 		SymKwDigest:  {"digest", SymClassOperator, PosInfix},
+		SymKwCat:     {"cat", SymClassOperator, PosInfix},
 		SymKwJoin:    {"join", SymClassOperator, PosInfix},
 		SymKwGroupBy: {"groupby", SymClassOperator, PosInfix},
 		SymKwFunc:    {"func(", SymClassDeclaration, PosPrefix},

scan/term.go

@@ -15,9 +15,9 @@ type TermPriority uint32
 const (
 	PriNone TermPriority = iota
 	PriRange
-	PriIterOp // map, filter, digest, etc
 	PriBut
 	PriAssign
+	PriIterOp // map, filter, digest, etc
 	PriInsert
 	PriOr
 	PriAnd

t_iterator_test.go

@@ -49,3 +49,14 @@ func TestIteratorParser(t *testing.T) {
 	// runTestSuiteSpec(t, section, inputs, 10)
 	runTestSuite(t, section, inputs)
 }
+
+func TestCatIterator(t *testing.T) {
+	section := "Iterator"
+	inputs := []inputType{
+		/*   1 */ {`([1] cat [2]) map $_`, kern.NewList([]any{int64(1), int64(2)}), nil},
+		/*   2 */ {`$$([1] cat [2])`, kern.NewList([]any{int64(1), int64(2)}), nil},
+	}
+
+	// runTestSuiteSpec(t, section, inputs, 2)
+	runTestSuite(t, section, inputs)
+}