FIX #202

allow interface method with empty (void) return type

-> only look for type declaration if no new line has been
   while skipping whitespace

compiler/parser.v

@@ -393,6 +393,25 @@ fn (p mut Parser) type_decl() {
 	p.table.register_type_with_parent(name, parent)
 }
 
+fn (p mut Parser) interface_method(field_name, receiver string) &Fn {
+	mut method := &Fn {
+		name: field_name
+		is_interface: true
+		is_method: true
+		receiver_typ: receiver
+	}
+	p.log('is interface. field=$field_name run=$p.run')
+	p.fn_args(mut method)
+	if p.scanner.has_gone_over_line_end() {
+		method.typ = 'void'
+	} else {
+		method.typ = p.get_type()// method return type
+		p.fspace()
+		p.fgenln('')
+	}
+	return method
+}
+
 // also unions and interfaces
 fn (p mut Parser) struct_decl() {
 	// Attribute before type?
@@ -525,18 +544,7 @@ fn (p mut Parser) struct_decl() {
 		// We are in an interface?
 		// `run() string` => run is a method, not a struct field
 		if is_interface {
-			mut interface_method := &Fn {
-				name: field_name
-				is_interface: true
-				is_method: true
-				receiver_typ: name
-			}
-			println('is interface. field=$field_name run=$p.run')
-			p.fn_args(mut interface_method)
-			p.fspace()
-			interface_method.typ = p.get_type()// method return type
-			typ.add_method(interface_method)
-			p.fgenln('')
+			typ.add_method(p.interface_method(field_name, name))
 			continue
 		}
 		// `pub` access mod

compiler/scanner.v

@@ -120,6 +120,20 @@ fn (s mut Scanner) ident_number() string {
 	return number
 }
 
+fn (s Scanner) has_gone_over_line_end() bool {
+	mut i := s.pos-1
+	for i >= 0 && !is_white(s.text[i]) {
+		i--
+	}
+	for i >= 0 && is_white(s.text[i]) {
+		if is_nl(s.text[i]) {
+			return true
+		}
+		i--
+	}
+	return false
+}
+
 fn (s mut Scanner) skip_whitespace() {
 	for s.pos < s.text.len && is_white(s.text[s.pos]) {
 		if is_nl(s.text[s.pos]) {
@@ -148,7 +162,8 @@ fn (s mut Scanner) cao_change(operator string) {
 	s.text = s.text.substr(0, s.pos - operator.len) + ' = ' + s.get_var_name(s.pos - operator.len) + ' ' + operator + ' ' + s.text.substr(s.pos + 1, s.text.len)
 }
 
-fn (s mut Scanner) scan() ScanRes {
+fn (s mut Scanner) scan() 
+ScanRes {
 	// if s.file_path == 'd.v' {
 	// println('\nscan()')
 	// }

compiler/tests/interface_test.v

@@ -0,0 +1,32 @@
+
+struct Dog {
+}
+
+fn (d Dog) speak() {
+	println('dog.speak()')
+}
+
+fn (d Dog) name() string {
+	return 'old gray'
+}
+
+interface Speaker {
+	name() string
+	speak() 
+}
+
+interface Speak2er {
+	speak() 
+	name() string
+}
+
+fn perform_speak(s Speaker) bool {
+	s.speak()
+	return true
+}
+
+fn test_perform_speak() {
+	d := Dog{}
+	assert perform_speak(d)
+}
+