dict: implemented sub-field access, e.g D=["sub-dict"]["sub-field"]

parser.go

@@ -6,6 +6,7 @@ package expr
 
 import (
 	"errors"
+	"slices"
 
 	"git.portale-stac.it/go-pkg/expr/scan"
 	"golang.org/x/exp/constraints"
@@ -401,7 +402,8 @@ func couldBeACollection(t *scan.Term) bool {
 	if t != nil {
 		sym = t.Symbol()
 	}
-	return sym == scan.SymList || sym == scan.SymString || sym == scan.SymDict || sym == scan.SymExpression || sym == scan.SymVariable
+	// return sym == scan.SymList || sym == scan.SymString || sym == scan.SymDict || sym == scan.SymExpression || sym == scan.SymVariable
+	return slices.Contains([]scan.Symbol{scan.SymList, scan.SymString, scan.SymDict, scan.SymExpression, scan.SymVariable, scan.SymIndex}, sym)
 }
 
 func listSubTree(tree *scan.Ast, listTerm *scan.Term, allowIndeces bool) (root *scan.Term, err error) {