func (self *Pair) Eval(env *scope.Scope) value.Value {
var first value.Value
var second value.Value
if self.Second == NilPair {
second = value.NilPairValue
} else {
switch self.Second.(type) {
case *Name:
second = value.NewSymbol(self.Second.(*Name).Identifier)
default:
second = self.Second.Eval(env)
}
}
if name, ok := self.First.(*Name); ok {
// treat Name as Symbol
first = value.NewSymbol(name.Identifier)
} else if _, ok := self.First.(*UnquoteSplicing); ok {
// our parser garantees unquote-splicing only appears in quasiquote
// and unquote-splicing will be evaluated to a list
first = self.First.Eval(env)
// () empty list must be handled
if first == value.NilPairValue {
return second
}
// seek for the last element
var last value.Value = first
for {
switch last.(type) {
case *value.PairValue:
pair := last.(*value.PairValue)
if pair.Second == value.NilPairValue {
pair.Second = second
return first
}
last = pair.Second
default:
if second == value.NilPairValue {
return first
} else {
// `(,@(cdr '(1 . 2) 3))
panic(fmt.Sprintf("unquote-splicing: expected list?, given: %s", first))
}
}
}
} else {
first = self.First.Eval(env)
}
return value.NewPairValue(first, second)
}
func (self *Cons) Apply(args []value.Value) value.Value {
if len(args) != 2 {
panic(fmt.Sprintf("cons: arguments mismatch, expected: 2, given: ", args))
}
return value.NewPairValue(args[0], args[1])
}