Add signatures to methods.

selsl/value/value.go

@@ -107,13 +107,14 @@ func (l List) String() string {
 
 type Method struct {
 	Object
-	Value func(env Value, self Value, args ...Value) List
+	Signature List
+	Value     func(env Value, self Value, args ...Value) List
 }
 
-func NewMethod(name string, members Members,
+func NewMethod(name string, members Members, signature List,
 	value func(env Value, self Value, args ...Value) List) Method {
 	return Method{Object: NewObject(name, MethodType, members),
-		Value: value}
+		Signature: signature, Value: value}
 }
 
 func (m Method) String() string {