new syntax to get items from collection: collection[index]. Supported collections are string, list and dict

parser.go

@@ -155,6 +155,7 @@ func (self *parser) parseFuncDef(scanner *scanner) (tree *term, err error) {
 }
 
 func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term, err error) {
+	r, c := scanner.lastPos()
 	args := make([]*term, 0)
 	lastSym := SymUnknown
 	itemExpected := false
@@ -179,7 +180,7 @@ func (self *parser) parseList(scanner *scanner, allowVarRef bool) (subtree *term
 		if lastSym != SymClosedSquare {
 			err = scanner.Previous().ErrorExpectedGot("]")
 		} else {
-			subtree = newListTerm(args)
+			subtree = newListTerm(r, c, args)
 		}
 	}
 	return
@@ -301,7 +302,7 @@ func (self *parser) parseSelectorCase(scanner *scanner, allowVarRef bool, defaul
 		startRow = tk.row
 		startCol = tk.col
 	} else if !defaultCase {
-		filterList = newListTerm(make([]*term, 0))
+		filterList = newListTerm(startRow, startCol, make([]*term, 0))
 	}
 
 	if tk.Sym == SymOpenBrace {
@@ -402,7 +403,19 @@ func (self *parser) parseGeneral(scanner *scanner, allowForest bool, allowVarRef
 		case SymOpenSquare:
 			var listTerm *term
 			if listTerm, err = self.parseList(scanner, allowVarRef); err == nil {
-				err = tree.addTerm(listTerm)
+				var sym = SymUnknown
+				if currentTerm != nil {
+					sym = currentTerm.symbol()
+				}
+				if sym == SymList || sym == SymString || sym == SymDict || sym == SymExpression {
+					indexTk := NewToken(listTerm.tk.row, listTerm.tk.col, SymIndex, listTerm.source())
+					indexTerm := newTerm(indexTk)
+					if err = tree.addTerm(indexTerm); err == nil {
+						err = tree.addTerm(listTerm)
+					}
+				} else {
+					err = tree.addTerm(listTerm)
+				}
 				currentTerm = listTerm
 			}
 		case SymOpenBrace: