From c9c58f90308058b5d1b4ead6c881a9e70e69d40f Mon Sep 17 00:00:00 2001
From: VaclavT <vaclavt@gmail.com>
Date: Mon, 22 Feb 2021 01:29:54 +0100
Subject: [PATCH] allow if without else

---
 ml.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/ml.cpp b/ml.cpp
index 7c912ff..3f9229d 100644
--- a/ml.cpp
+++ b/ml.cpp
@@ -887,12 +887,15 @@ namespace builtin {
 
     // if-else (SPECIAL FORM)
     MlValue if_then_else(std::vector<MlValue> args, MlEnvironment &env) {
-	    if (args.size() != 3)
+	    if (args.size() != 2 && args.size() != 3)
 		    throw MlError(MlValue("if", if_then_else), env, args.size() > 3 ? TOO_MANY_ARGS : TOO_FEW_ARGS);
 
 	    if (args[0].eval(env).as_bool())
 		    return args[1].eval(env);
-	    else return args[2].eval(env);
+	    else if (args.size() == 3)
+			return args[2].eval(env);
+
+		return MlValue(0);
     }
 
     // Define a variable with a value (SPECIAL FORM)
@@ -1423,6 +1426,7 @@ namespace builtin {
 
 	    if (args.size() == 0)
 		    throw MlError(MlValue("push", push), env, TOO_FEW_ARGS);
+
 	    for (size_t i = 1; i < args.size(); i++)
 		    args[0].push(args[i]);
 	    return args[0];