lexing for hidden names

ex.moon

@@ -34,3 +34,24 @@ item_one: "this is item one"
 
 # we may reference an item that was defined earlier
 item_two: item_one
+
+# items can be hidden.  i.e., they're only valid in the parse and eval stage as
+# intermediate values internal to the config file; they are *not* visible to
+# the host program.  This is generally useful for composing larger, more
+# complicated things.
+.hidden_item: "it has a value"
+visible_item: .hidden_item
+
+.person_one: {
+    name: "the first name here"
+    age: 28
+    hometown: "crooklyn"
+}
+
+.person_two: {
+    name: "the second name here"
+    age: 30
+    hometown: "tha bronx"
+}
+
+people: [.person_one .person_two]

lex.go

@@ -110,6 +110,12 @@ func (l *lexer) next() rune {
 	return r
 }
 
+func (l *lexer) peek() rune {
+	r := l.next()
+	l.unread(r)
+	return r
+}
+
 func (l *lexer) keep(r rune) {
 	if l.buf == nil {
 		l.buf = make([]rune, 0, 18)
@@ -211,7 +217,10 @@ func lexRoot(l *lexer) stateFn {
 		l.keep(r)
 		l.emit(t_object_separator)
 		return lexRoot
-	case strings.IndexRune(".+-0123456789", r) >= 0:
+	case r == '.':
+		l.keep(r)
+		return lexAfterPeriod
+	case strings.IndexRune("+-0123456789", r) >= 0:
 		l.unread(r)
 		return lexNumber
 	case unicode.IsSpace(r):
@@ -227,6 +236,20 @@ func lexRoot(l *lexer) stateFn {
 	}
 }
 
+func lexAfterPeriod(l *lexer) stateFn {
+	r := l.next()
+	switch {
+	case strings.IndexRune("+-0123456789", r) >= 0:
+		l.unread(r)
+		return lexNumber
+	case unicode.IsLower(r):
+		l.keep(r)
+		return lexName
+	default:
+		return lexErrorf("unexpected rune after period: %c", r)
+	}
+}
+
 func lexComment(l *lexer) stateFn {
 	switch r := l.next(); r {
 	case '\n':

node.go

@@ -201,6 +201,10 @@ func (n *assignmentNode) eval(ctx map[string]interface{}) (interface{}, error) {
 	return nil, nil
 }
 
+func (n *assignmentNode) isHidden() bool {
+	return strings.HasPrefix(n.name, ".")
+}
+
 type stringNode string
 
 func (s *stringNode) Type() nodeType {
@@ -442,7 +446,3 @@ func (v *variableNode) eval(ctx map[string]interface{}) (interface{}, error) {
 	}
 	return value, nil
 }
-
-func (v *variableNode) isHidden() bool {
-	return strings.HasPrefix(v.name, ".")
-}