pec-0.1.1: lib/Stack.pec

module Stack

exports (Stack, stack, push, pop, is_empty, is_full)
// explicit export list

where

import Prelude

type Stck #cnt a = { height :: W32, data :: Array cnt a }
// stacks are polymorphic in their size and what they contain

type Stack #cnt a = Stck cnt a

>type Stack cnt a = Stack_ cnt a
>
>stack_ :: (Count cnt, Typed cnt, Typed a) => Term (cnt -> Stack cnt a)
>stack_ = lam_ $ \_ -> lift $ do
>  p <- eval $ alloca unused
>  eval_ $ store (height_get p) (int 0)
>  return $ load p
>
>push_ :: (Count cnt, Typed cnt, Typed a) =>
>  Term (a -> Ptr (Stack cnt a) -> Bool_)
>push_ = lam2_ $ \a (p :: Term (Ptr (Stack cnt a))) ->
>  app3 if_ (app is_full_ p)
>    false_
>    (lift (do i <- eval $ load (height_get p)
>              evalv $ store (idx (data_get p) (cast i)) a
>              evalv $ store (height_get p) (add i (int 1))
>              return true_
>          ))
> 
>pop_ :: (Count cnt, Typed cnt, Typed a) =>
>  Term (Ptr (Stack cnt a) -> Maybe_ a)
>pop_ = lam_ $ \p -> app3 if_ (app is_empty_ p)
>  nothing_
>  (lift (do i <- eval $ sub (load (height_get p)) (int 1)
>            evalv $ store (height_get p) i
>            return $ app just_ (load (idx (data_get p) (cast i)))
>        ))
>
>is_empty_ :: (Count cnt, Typed cnt, Typed a) =>
>  Term (Ptr (Stack cnt a) -> Bool_)
>is_empty_ = lam_ $ \p -> eq (load (height_get p)) (int 0)
>
>is_full_ :: (Count cnt, Typed cnt, Typed a) =>
>  Term (Ptr (Stack cnt a) -> Bool_)
>is_full_ = lam_ $ \(p :: Term (Ptr (Stack cnt a))) ->
>  eq (load (height_get p)) (int $ countof (unused :: cnt))