func (self *LetStar) Eval(env *scope.Scope) value.Value {
// Let* is similar to let, but the bindings are performed sequentially
// from left to right, and the region of a binding indicated by
// (<variable> <init>) is that part of the let* expression to the right
// of the binding. Thus the second binding is done in an environment in
// which the first binding is visible, and so on.
for i := 0; i < len(self.Patterns); i++ {
env = scope.NewScope(env)
binder.Define(env, self.Patterns[i].Identifier, self.Exprs[i].Eval(env))
}
return self.Body.Eval(env)
}
func (self *Let) Eval(s *scope.Scope) value.Value {
// The <init>s are evaluated in the current environment
// (in some unspecified order), the <variable>s are bound
// to fresh locations holding the results, the <body> is
// evaluated in the extended environment, and the value(s)
// of the last expression of <body> is(are) returned.
env := scope.NewScope(s)
extended := scope.NewScope(s)
for i := 0; i < len(self.Patterns); i++ {
binder.Define(extended, self.Patterns[i].Identifier, self.Exprs[i].Eval(env))
}
return self.Body.Eval(extended)
}
func (self *LetRec) Eval(s *scope.Scope) value.Value {
// The <variable>s are bound to fresh locations holding undefined values,
// the <init>s are evaluated in the resulting environment
// (in some unspecified order), each <variable> is assigned to the result of
// the corresponding <init>, the <body> is evaluated in the resulting
// environment, and the value(s) of the last expression in <body> is(are)
// returned. Each binding of a <variable> has the entire letrec expression
// as its region, making it possible to define mutually recursive procedures.
env := scope.NewScope(s)
extended := make([]*scope.Scope, len(self.Patterns))
for i := 0; i < len(self.Patterns); i++ {
extended[i] = scope.NewScope(env)
binder.Define(extended[i], self.Patterns[i].Identifier, self.Exprs[i].Eval(env))
}
for i := 0; i < len(extended); i++ {
env.PutAll(extended[i])
}
return self.Body.Eval(env)
}
func (self *Define) Eval(env *scope.Scope) value.Value {
binder.Define(env, self.Pattern.Identifier, self.Value.Eval(env))
return nil
}