new operator dot '.' used to select an item or character from a list or a string respectively

operator-dot.go

@@ -0,0 +1,61 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-dot.go
+package expr
+
+// -------- dot term
+func newDotTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priDot,
+		evalFunc: evalDot,
+	}
+}
+
+func evalDot(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	indexTerm := self.children[1]
+	if !isInteger(rightValue) {
+		err = indexTerm.Errorf("index expression must be integer, got %T", rightValue)
+		return
+	}
+
+	index64, _ := rightValue.(int64)
+	index := int(index64)
+
+	if isList(leftValue) {
+		list, _ := leftValue.([]any)
+		if index >= 0 && index < len(list) {
+			v = list[index]
+		} else if index >= -len(list) {
+			v = list[len(list)+index]
+		} else {
+			err = indexTerm.Errorf("index %v out of bounds", index)
+		}
+	} else if isString(leftValue) {
+		s, _ := leftValue.(string)
+		if index >= 0 && index < len(s) {
+			v = string(s[index])
+		} else if index >= -len(s) {
+			v = string(s[len(s)+index])
+		} else {
+			err = indexTerm.Errorf("index %v out of bounds", index)
+		}
+	} else {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymDot, newDotTerm)
+}

operator-insert.go

@@ -4,7 +4,6 @@
 // operator-insert.go
 package expr
 
-
 //-------- insert term
 
 func newInsertTerm(tk *Token) (inst *term) {
@@ -12,7 +11,7 @@ func newInsertTerm(tk *Token) (inst *term) {
 		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
-		priority: priSign,
+		priority: priAssign,
 		evalFunc: evalInsert,
 	}
 }
@@ -22,7 +21,7 @@ func newAppendTerm(tk *Token) (inst *term) {
 		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
-		priority: priSign,
+		priority: priAssign,
 		evalFunc: evalAppend,
 	}
 }
@@ -38,7 +37,7 @@ func evalInsert(ctx ExprContext, self *term) (v any, err error) {
 		list, _ := rightValue.([]any)
 		v = append([]any{leftValue}, list...)
 	} else {
-		err = self.errIncompatibleType(rightValue)
+		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }
@@ -54,7 +53,7 @@ func evalAppend(ctx ExprContext, self *term) (v any, err error) {
 		list, _ := leftValue.([]any)
 		v = append(list, rightValue)
 	} else {
-		err = self.errIncompatibleType(leftValue)
+		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
 	return
 }

scanner.go

@@ -152,9 +152,10 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 		case ';':
 			tk = self.makeToken(SymSemiColon, ch)
 		case '.':
-			if next, _ := self.peek(); next >= '0' && next <= '9' {
-				tk = self.parseNumber(ch)
-			} else if next == '/' {
+			//if next, _ := self.peek(); next >= '0' && next <= '9' {
+			//	tk = self.parseNumber(ch)
+			//} else if next == '/' {
+			if next, _ := self.peek(); next == '/' {
 				tk = self.moveOn(SymDotSlash, ch, next)
 			} else {
 				tk = self.makeToken(SymDot, ch)

term.go

@@ -24,6 +24,7 @@ const (
 	priSign
 	priFact
 	priCoalesce
+	priDot
 	priValue
 )
 
@@ -166,7 +167,7 @@ func (self *term) checkOperands() (err error) {
 	switch self.position {
 	case posInfix:
 		if self.children == nil || len(self.children) != 2 || self.anyChildrenNil() {
-			err = self.tk.Errorf("infix operator %q requires two not nil operands, got %d", self.source(), self.getChildrenCount())
+			err = self.tk.Errorf("infix operator %q requires two non-nil operands, got %d", self.source(), self.getChildrenCount())
 		}
 	case posPrefix:
 		if self.children == nil || len(self.children) != 1 || self.children[0] == nil {