func Eval(sc *scheme.Scope, e scheme.Sexpr) (scheme.Sexpr, error) {
//e = transform(sc, e)
switch e := e.(type) {
case *scheme.Cons:
cons := e
car, err := Eval(sc, cons.Car)
if err != nil {
return nil, err
}
if !isFunction(car) && !isPrim(car) {
return nil, evalError("Attempted application on non-function")
}
cdr := cons.Cdr
args, err := scheme.Flatten(cdr)
if err != nil {
return nil, err
}
if isPrim(car) {
return car.(*scheme.Primitive).Procedure()(sc, args)
}
f := car.(*scheme.Function).Procedure()
for i, a := range args {
args[i], err = Eval(sc, a)
if err != nil {
return nil, err
}
}
return f(sc, args)
case *scheme.Symbol:
return sc.Lookup(e)
}
return e, nil
}
func let(s *scheme.Scope, ss []scheme.Sexpr) (scheme.Sexpr, error) {
if len(ss) < 1 {
return nil, scheme.ProcError("let requires at least one argument")
}
evalScope := scheme.NewScope(s)
bindings, err := scheme.Flatten(ss[0])
if err != nil {
return nil, err
}
for _, b := range bindings {
bs, err := scheme.Flatten(b)
if err != nil {
return nil, err
}
if len(bs) != 2 {
return nil, scheme.ProcError("invalid binding on let")
}
sym, ok := bs[0].(*scheme.Symbol)
if !ok {
return nil, scheme.ProcError("invalid binding on let")
}
val, err := eval.Eval(s, bs[1])
if err != nil {
return nil, err
}
evalScope.Define(sym, val)
}
prog := ss[1:]
var last scheme.Sexpr = scheme.Nil
for _, l := range prog {
last, err = eval.Eval(evalScope, l)
if err != nil {
return nil, err
}
}
return last, nil
}