Allow binding NIL in environments.

2 files changed, 8 insertions, 3 deletions

diff --git a/MLKEnvironment.m b/MLKEnvironment.m
index 2dab2aa..581c462 100644
--- a/MLKEnvironment.m
+++ b/MLKEnvironment.m
@@ -74,7 +74,9 @@ static id UNBOUND;
 
 -(void) setValue:(id)value forBinding:(MLKSymbol *)symbol;
 {
-  [self setBinding:symbol to:value inEnvironment:self];
+  [self setBinding:(symbol ? (id)symbol : (id)[NSNull null])
+        to:value
+        inEnvironment:self];
 }
 
 -(void) setBinding:(MLKSymbol *)symbol to:(id)value inEnvironment:(MLKEnvironment *)env
@@ -93,7 +95,8 @@ static id UNBOUND;
 
 -(id) valueForBinding:(MLKSymbol *)symbol
 {
-  return [self valueForBinding:symbol inEnvironment:self];
+  return [self valueForBinding:(symbol ? (id)symbol : (id)[NSNull null])
+               inEnvironment:self];
 }
 
 -(id) valueForBinding:(MLKSymbol *)symbol inEnvironment:(MLKEnvironment *)env
@@ -134,7 +137,7 @@ static id UNBOUND;
 
 -(void) addBinding:(MLKSymbol *)symbol
 {
-  [_bindings setObject:UNBOUND forKey:symbol];
+  [_bindings setObject:UNBOUND forKey:(symbol ? (id)symbol : (id)[NSNull null])];
 }
 
 -(MLKEnvironment *) environmentForBinding:(MLKSymbol *)symbol
diff --git a/MLKInterpreter.m b/MLKInterpreter.m
index 1f158ec..a8b94ee 100644
--- a/MLKInterpreter.m
+++ b/MLKInterpreter.m
@@ -48,6 +48,7 @@ static MLKSymbol *FUNCALL;
 static MLKSymbol *EVAL;
 static MLKSymbol *QUOTE;
 static MLKSymbol *SETQ;
+static MLKSymbol *PROGV;
 static MLKSymbol *_DEFMACRO;
 
 
@@ -69,6 +70,7 @@ static MLKSymbol *_DEFMACRO;
   EVAL = [cl intern:@"EVAL"];
   QUOTE = [cl intern:@"QUOTE"];
   SETQ = [cl intern:@"SETQ"];
+  PROGV = [cl intern:@"PROGV"];
   _DEFMACRO = [sys intern:@"%DEFMACRO"];
 }