From ab8264f8be5ca10d27a7061ea81197ffe356f81a Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 14 May 2020 17:50:48 +0200
Subject: [PATCH] docs: interfaces: is

---
 doc/docs.md | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/doc/docs.md b/doc/docs.md
index fc4658739e..18d24cb03d 100644
--- a/doc/docs.md
+++ b/doc/docs.md
@@ -1003,6 +1003,11 @@ interface Speaker {
 }
 
 fn perform(s Speaker) string {
+    if s is Dog { // use `is` to check the underlying type of an interface
+        println('perform(dog)')
+    } else if s is Cat {
+        println('perform(cat)')
+    }
     return s.speak()
 }
 
@@ -1042,7 +1047,7 @@ struct CallExpr {
 	...
 }
 
-fn (p mut Parser) expr(precedence int) ast.Expr {
+fn (p mut Parser) expr(precedence int) Expr {
 	match p.tok {
 		.key_if { return IfExpr{} }
 		...
@@ -1052,7 +1057,7 @@ fn (p mut Parser) expr(precedence int) ast.Expr {
 
 fn gen(expr Expr) {
 	match expr {
-		.key_if { gen_if(it) }
+		IfExpr { gen_if(it) }
 		...
 	}
 }