Language/Symantic/Expr/Lambda.hs

   1 {-# LANGUAGE DefaultSignatures #-}
   2 {-# LANGUAGE FlexibleContexts #-}
   3 {-# LANGUAGE FlexibleInstances #-}
   4 {-# LANGUAGE MultiParamTypeClasses #-}
   5 {-# LANGUAGE Rank2Types #-}
   6 {-# LANGUAGE ScopedTypeVariables #-}
   7 {-# LANGUAGE TypeFamilies #-}
   8 -- | Expression for /lambda abstraction/s
   9 -- in /Higher-Order Abstract Syntax/ (HOAS).
  10 module Language.Symantic.Expr.Lambda where
  11
  12 import Data.Proxy (Proxy(..))
  13 import Data.Type.Equality ((:~:)(Refl))
  14 import Data.Text (Text)
  15
  16 import Language.Symantic.Type
  17 import Language.Symantic.Expr.Common
  18 import Language.Symantic.Repr.Dup
  19 import Language.Symantic.Trans.Common
  20
  21 -- * Class 'Sym_Lambda'
  22
  23 -- | Symantic.
  24 --
  25 -- NOTE: argument @arg@ and result @res@ of 'Lambda'
  26 -- wrapped inside 'lam': to control the calling
  27 -- in the 'Repr_Host' instance.
  28 --
  29 -- NOTE: the default definitions supplied for:
  30 -- 'app', 'inline', 'val' and 'lazy'
  31 -- are there to avoid boilerplate code
  32 -- when writting 'Trans' instances which
  33 -- do not need to alterate those methods.
  34 class (lam ~ Lambda_from_Repr repr) => Sym_Lambda lam repr where
  35         -- | This type constructor is used like
  36         -- the functional dependency: @repr -> lam@
  37         -- (ie. knowing @repr@ one can determine @lam@)
  38         -- in order to avoid to introduce a 'Proxy' @lam@
  39         -- in 'let_inline', 'let_val' and 'let_lazy'.
  40         --
  41         -- Distinguishing between @lam@ and @repr@ is used to maintain
  42         -- the universal polymorphism of @repr@ in 'Expr_from',
  43         -- the downside with this however is that
  44         -- to be an instance of 'Sym_Lambda' for all @lam@,
  45         -- the @repr@ type of an interpreter
  46         -- has to be parameterized by @lam@,
  47         -- even though it does not actually need @lam@ to do its work.
  48         --
  49         -- Basically this means having sometimes to add a type annotation
  50         -- to the interpreter call to specify @lam@.
  51         type Lambda_from_Repr repr :: {-lam-}(* -> *)
  52
  53         -- | /Lambda application/.
  54         app :: repr (Lambda lam arg res) -> repr arg -> repr res
  55
  56         -- | /Call-by-name/ /lambda abstraction/.
  57         inline :: (repr arg -> repr res) -> repr (Lambda lam arg res)
  58         -- | /Call-by-value/ /lambda abstraction/.
  59         val    :: (repr arg -> repr res) -> repr (Lambda lam arg res)
  60         -- | /Call-by-need/ /lambda abstraction/ (aka. /lazyness/): lazy shares its argument, no matter what.
  61         lazy   :: (repr arg -> repr res) -> repr (Lambda lam arg res)
  62
  63         default app    :: Trans t repr => t repr (Lambda lam arg res) -> t repr arg -> t repr res
  64         default inline :: Trans t repr => (t repr arg -> t repr res) -> t repr (Lambda lam arg res)
  65         default val    :: Trans t repr => (t repr arg -> t repr res) -> t repr (Lambda lam arg res)
  66         default lazy   :: Trans t repr => (t repr arg -> t repr res) -> t repr (Lambda lam arg res)
  67         app  f x = trans_lift $ trans_apply f `app` trans_apply x
  68         inline f = trans_lift $ inline $ trans_apply . f . trans_lift
  69         val    f = trans_lift $ val    $ trans_apply . f . trans_lift
  70         lazy   f = trans_lift $ lazy   $ trans_apply . f . trans_lift
  71
  72         -- | Convenient 'inline' wrapper.
  73         let_inline
  74          :: Sym_Lambda lam repr
  75          => repr var -> (repr var -> repr res) -> repr res
  76         let_inline x y = inline y `app` x
  77         -- | Convenient 'val' wrapper.
  78         let_val
  79          :: Sym_Lambda lam repr
  80          => repr var -> (repr var -> repr res) -> repr res
  81         let_val x y = val y `app` x
  82         -- | Convenient 'lazy' wrapper.
  83         let_lazy
  84          :: Sym_Lambda lam repr
  85          => repr var -> (repr var -> repr res) -> repr res
  86         let_lazy x y = lazy y `app` x
  87
  88 infixl 5 `app`
  89
  90 instance -- Sym_Lambda Dup
  91  ( Sym_Lambda lam r1
  92  , Sym_Lambda lam r2
  93  ) => Sym_Lambda lam (Dup r1 r2) where
  94         type Lambda_from_Repr (Dup r1 r2) = Lambda_from_Repr r1
  95         app (f1 `Dup` f2) (x1 `Dup` x2) = app f1 x1 `Dup` app f2 x2
  96         inline f = dup1 (inline f) `Dup` dup2 (inline f)
  97         val    f = dup1 (val f)    `Dup` dup2 (val f)
  98         lazy   f = dup1 (lazy f)   `Dup` dup2 (lazy f)
  99
 100 -- * Type 'Expr_Lambda'
 101 -- | Expression.
 102 data Expr_Lambda (lam:: * -> *) (root:: *)
 103 type instance Root_of_Expr      (Expr_Lambda lam root)      = root
 104 type instance Type_of_Expr      (Expr_Lambda lam root)      = Type_Fun lam
 105 type instance Sym_of_Expr       (Expr_Lambda lam root) repr = Sym_Lambda lam repr
 106 type instance Error_of_Expr ast (Expr_Lambda lam root)      = Error_Expr_Lambda ast
 107
 108 -- | Parse a /lambda variable/.
 109 var_from
 110  :: forall ast lam root hs ret.
 111  ( Type_from ast (Type_Root_of_Expr root)
 112  , Error_Expr_Lift (Error_Expr_Lambda ast)
 113                    (Error_of_Expr ast root)
 114  , Root_of_Expr root ~ root
 115  ) => Text -> Expr_From ast (Expr_Lambda lam root) hs ret
 116 var_from name _ex ast = go
 117         where
 118         go :: forall ex hs'. (ex ~ (Expr_Lambda lam root))
 119          => Context (Lambda_Var (Type_Root_of_Expr ex)) hs'
 120          -> ( forall h. Type_Root_of_Expr ex h
 121             -> Forall_Repr_with_Context ex hs' h
 122             -> Either (Error_of_Expr ast (Root_of_Expr ex)) ret )
 123          ->    Either (Error_of_Expr ast (Root_of_Expr ex)) ret
 124         go c k' =
 125                 case c of
 126                  Context_Empty -> Left $ error_expr_lift $
 127                         Error_Expr_Lambda_Var_unbound name ast
 128                  Lambda_Var n ty `Context_Next` _ | n == name ->
 129                         k' ty $ Forall_Repr_with_Context $
 130                          \(repr `Context_Next` _) -> repr
 131                  _ `Context_Next` ctx' ->
 132                         go ctx' $ \ty (Forall_Repr_with_Context repr) ->
 133                                 k' ty $ Forall_Repr_with_Context $
 134                                  \(_ `Context_Next` c') -> repr c'
 135
 136 -- | Parse a /lambda application/.
 137 app_from
 138  :: forall ty ast lam root hs ret.
 139  ( ty ~ Type_Root_of_Expr root
 140  , Type_from ast ty
 141  , Expr_from ast root
 142  , Type_Root_Lift (Type_Fun lam) ty
 143  , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
 144                    (Error_of_Expr ast root)
 145  , Type_Unlift (Type_Fun lam) (Type_of_Expr root)
 146  , Root_of_Expr root ~ root
 147  ) => ast -> ast
 148  -> Expr_From ast (Expr_Lambda lam root) hs ret
 149 app_from ast_lam ast_arg_actual ex ast ctx k =
 150         expr_from (Proxy::Proxy root) ast_lam ctx $
 151          \(ty_lam::Type_Root_of_Expr root h_lam) (Forall_Repr_with_Context lam) ->
 152         expr_from (Proxy::Proxy root) ast_arg_actual ctx $
 153          \(ty_arg_actual::Type_Root_of_Expr root h_arg_actual)
 154           (Forall_Repr_with_Context arg_actual) ->
 155                 case type_unlift $ unType_Root ty_lam of
 156                  Nothing -> Left $
 157                         error_expr ex $
 158                         Error_Expr_Type_mismatch ast
 159                          (Exists_Type (type_var SZero `type_fun` type_var (SSucc SZero)
 160                          :: Type_Root_of_Expr (Expr_Lambda lam root) (lam Zero -> lam (Succ Zero))))
 161                          (Exists_Type ty_lam)
 162                  Just (ty_arg_expected `Type_Fun` ty_res
 163                   :: Type_Fun lam (Type_Root_of_Expr root) h_lam) ->
 164                         when_type_eq ex ast
 165                          ty_arg_expected ty_arg_actual $ \Refl ->
 166                                 k ty_res $ Forall_Repr_with_Context $
 167                                  \c -> lam c `app` arg_actual c
 168
 169 -- | Parse a /lambda abstraction/.
 170 lam_from
 171  :: forall ty ast lam root hs ret.
 172  ( ty ~ Type_Root_of_Expr root
 173  , Type_from ast ty
 174  , Expr_from ast root
 175  , Type_Root_Lift (Type_Fun lam) ty
 176  , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
 177                    (Error_of_Expr ast root)
 178  , Root_of_Expr root ~ root
 179  ) => (forall repr arg res
 180       . Sym_Lambda lam repr
 181       => (repr arg -> repr res)
 182       -> repr (Lambda lam arg res))
 183  -> Text -> ast -> ast
 184  -> Expr_From ast (Expr_Lambda lam root) hs ret
 185 lam_from lam name ast_ty_arg ast_body ex ast ctx k =
 186         case type_from
 187          (Proxy::Proxy (Type_Root_of_Expr root))
 188          ast_ty_arg (Right . Exists_Type) of
 189          Left err -> Left $ error_expr ex $ Error_Expr_Type err ast
 190          Right (Exists_Type (ty_arg::Type_Root_of_Expr root h_arg)) ->
 191                 expr_from (Proxy::Proxy root) ast_body
 192                  (Lambda_Var name ty_arg `Context_Next` ctx) $
 193                  \(ty_res::Type_Root_of_Expr root h_res) (Forall_Repr_with_Context res) ->
 194                         k (ty_arg `type_fun` ty_res
 195                          :: Root_of_Type (Type_Root_of_Expr root)
 196                                          (Lambda lam h_arg h_res)) $
 197                         Forall_Repr_with_Context $
 198                          \c -> lam $
 199                                  \arg -> res (arg `Context_Next` c)
 200
 201 -- | Parse a /let/.
 202 let_from
 203  :: forall ty ast lam root hs ret.
 204  ( ty ~ Type_Root_of_Expr root
 205  , Type_from ast ty
 206  , Expr_from ast root
 207  , Type_Root_Lift (Type_Fun lam) ty
 208  , Error_Expr_Lift (Error_Expr (Error_of_Type ast ty) ty ast)
 209                    (Error_of_Expr ast root)
 210  , Root_of_Expr root ~ root
 211  ) => (forall repr var res. Sym_Lambda lam repr
 212       => repr var -> (repr var -> repr res) -> repr res)
 213  -> Text -> ast -> ast
 214  -> Expr_From ast (Expr_Lambda lam root) hs ret
 215 let_from let_ name ast_var ast_body _ex _ast ctx k =
 216         expr_from (Proxy::Proxy root) ast_var ctx $
 217          \(ty_var::Type_Root_of_Expr root h_var) (Forall_Repr_with_Context var) ->
 218                 expr_from (Proxy::Proxy root) ast_body
 219                  (Lambda_Var name ty_var `Context_Next` ctx) $
 220                  \(ty_res::Type_Root_of_Expr root h_res) (Forall_Repr_with_Context res) ->
 221                         k ty_res $ Forall_Repr_with_Context $
 222                          \c -> let_ (var c) $
 223                                  \arg -> res (arg `Context_Next` c)
 224
 225 -- * Type 'Error_Expr_Lambda'
 226 data Error_Expr_Lambda ast
 227  =   Error_Expr_Lambda_Var_unbound Lambda_Var_Name ast
 228  deriving (Eq, Show)