Language/Symantic/Expr/From.hs

   1 {-# LANGUAGE ConstraintKinds #-}
   2 {-# LANGUAGE DataKinds #-}
   3 {-# LANGUAGE FlexibleContexts #-}
   4 {-# LANGUAGE FlexibleInstances #-}
   5 {-# LANGUAGE GADTs #-}
   6 {-# LANGUAGE KindSignatures #-}
   7 {-# LANGUAGE MultiParamTypeClasses #-}
   8 {-# LANGUAGE Rank2Types #-}
   9 {-# LANGUAGE ScopedTypeVariables #-}
  10 {-# LANGUAGE TypeFamilies #-}
  11 {-# LANGUAGE TypeOperators #-}
  12 {-# LANGUAGE UndecidableInstances #-}
  13 module Language.Symantic.Expr.From where
  14
  15 import Data.Maybe (fromMaybe)
  16 import Data.Proxy (Proxy(..))
  17 import Data.Text (Text)
  18 import Data.Type.Equality ((:~:)(Refl))
  19 import GHC.Prim (Constraint)
  20
  21 import Language.Symantic.Type
  22 import Language.Symantic.Expr.Root
  23 import Language.Symantic.Expr.Alt
  24 import Language.Symantic.Expr.Error
  25
  26 -- * Class 'Expr_from'
  27 -- | Parse given @ast@ into
  28 -- a 'Type_Root_of_Expr' and
  29 -- a 'Forall_Repr_with_Context',
  30 -- or return an 'Error_of_Expr'.
  31 class Expr_from ast (ex:: *) where
  32         expr_from :: Expr_From ast ex hs ret
  33 instance -- Expr_from
  34  ( Expr_from ast (ex (Expr_Root ex))
  35  , Root_of_Expr (ex (Expr_Root ex)) ~ Expr_Root ex
  36  ) => Expr_from ast (Expr_Root ex) where
  37         expr_from _ex ctx ast k =
  38                 expr_from (Proxy::Proxy (ex (Expr_Root ex)))
  39                  ctx ast $ \ty (Forall_Repr_with_Context repr) ->
  40                         k ty (Forall_Repr_with_Context repr)
  41 instance -- Expr_from
  42  ( Expr_from ast (curr root)
  43  , Expr_from ast (next root)
  44  , Root_of_Expr (curr root) ~ root
  45  , Root_of_Expr (next root) ~ root
  46  , Unlift_Error_Expr (Error_Expr (Error_of_Type ast (Type_Root_of_Expr root))
  47                                  (Type_Root_of_Expr root) ast)
  48                      (Error_of_Expr ast root)
  49  ) => Expr_from ast (Expr_Alt curr next root) where
  50         expr_from _ex ctx ast k =
  51                 case expr_from (Proxy::Proxy (curr root)) ctx ast $
  52                  \ty (Forall_Repr_with_Context repr) ->
  53                         Right $ k ty (Forall_Repr_with_Context repr) of
  54                  Right ret -> ret
  55                  Left err ->
  56                         case unlift_error_expr err of
  57                          Just (Error_Expr_Unsupported_here _
  58                           :: Error_Expr (Error_of_Type ast (Type_Root_of_Expr root))
  59                                         (Type_Root_of_Expr root) ast) ->
  60                                 expr_from (Proxy::Proxy (next root)) ctx ast $
  61                                  \ty (Forall_Repr_with_Context repr) ->
  62                                         k ty (Forall_Repr_with_Context repr)
  63                          _ -> Left err
  64
  65 -- ** Type 'Expr_From'
  66 type Expr_From ast ex hs ret
  67  = Proxy ex
  68  -- ^ Select the 'Expr_from' instance.
  69  -> ast
  70  -- ^ The input data to parse.
  71  -> Context (Lambda_Var (Type_Root_of_Expr ex)) hs
  72  -- ^ The bound variables in scope and their types:
  73  -- held in the heterogeneous list @hs@,
  74  -- from the closest including lambda abstraction to the farest.
  75  -> ( forall h
  76     .  Type_Root_of_Expr ex h
  77     -> Forall_Repr_with_Context ex hs h
  78     -> Either (Error_of_Expr ast (Root_of_Expr ex)) ret )
  79  -- ^ The accumulating continuation.
  80  ->    Either (Error_of_Expr ast (Root_of_Expr ex)) ret
  81
  82 -- ** Type 'Context'
  83 -- | GADT for a typing context,
  84 -- accumulating an @item@ at each lambda;
  85 -- used to accumulate object-types (in 'Expr_from')
  86 -- or host-terms (in 'Repr_Host')
  87 -- associated with the 'Lambda_Var's in scope.
  88 data Context :: (* -> *) -> [*] -> * where
  89         Context_Empty :: Context item '[]
  90         Context_Next  :: item h -> Context item hs -> Context item (h ': hs)
  91 infixr 5 `Context_Next`
  92
  93 -- ** Type 'Lambda_Var'
  94 -- | Join a name and a type.
  95 --
  96 -- This data type is used to handle lambda variables by name
  97 -- (instead of DeBruijn indices for instance).
  98 data Lambda_Var ty h
  99  =   Lambda_Var Lambda_Var_Name (ty h)
 100 type Lambda_Var_Name = Text
 101
 102 -- ** Type 'Forall_Repr_with_Context'
 103 -- | A data type embedding a universal quantification
 104 -- over an interpreter @repr@
 105 -- and qualified by the symantics of an expression.
 106 --
 107 -- Moreover the expression is abstracted by a 'Context'
 108 -- built at parsing time to build a /Higher-Order Abstract Syntax/ (HOAS)
 109 -- for lambda abstractions.
 110 --
 111 -- This data type is used to keep a parsed expression polymorphic enough
 112 -- to stay interpretable by different interpreters.
 113 --
 114 -- NOTE: 'Sym_of_Expr'@ ex repr@
 115 -- is needed to be able to use symantic methods of the parsed expression
 116 -- into a 'Forall_Repr_with_Context'@ ex@.
 117 --
 118 -- NOTE: 'Sym_of_Expr'@ (@'Root_of_Expr'@ ex) repr@
 119 -- is needed to be able to use an expression
 120 -- out of a 'Forall_Repr_with_Context'@ (@'Root_of_Expr'@ ex)@
 121 -- into a 'Forall_Repr_with_Context'@ ex@,
 122 -- which happens when a symantic method includes a polymorphic type
 123 -- and thus calls: 'expr_from'@ (Proxy::Proxy (@'Root_of_Expr'@ ex))@.
 124 data Forall_Repr_with_Context ex hs h
 125  =   Forall_Repr_with_Context
 126  (   forall repr. ( Sym_of_Expr ex repr
 127                   , Sym_of_Expr (Root_of_Expr ex) repr
 128                   ) => Context repr hs -> repr h )
 129
 130 -- ** Type 'Forall_Repr'
 131 data Forall_Repr ex h
 132  =   Forall_Repr
 133  { unForall_Repr :: forall repr
 134                  .  ( Sym_of_Expr ex repr
 135                     , Sym_of_Expr (Root_of_Expr ex) repr )
 136                  => repr h }
 137
 138 -- ** Type family 'Sym_of_Expr'
 139 -- | The symantic of an expression.
 140 type family Sym_of_Expr (ex:: *) (repr:: * -> *) :: Constraint
 141 type instance Sym_of_Expr (Expr_Root ex) repr
 142  =            Sym_of_Expr (ex (Expr_Root ex)) repr
 143 type instance Sym_of_Expr (Expr_Alt curr next root) repr
 144  = ( Sym_of_Expr (curr root) repr
 145    , Sym_of_Expr (next root) repr
 146    )
 147
 148 -- * Checks
 149
 150 -- | Parsing utility to check that two types are equal,
 151 -- or raise 'Error_Expr_Type_mismatch'.
 152 check_eq_type
 153  :: forall ast ex root ty x y ret.
 154  ( root ~ Root_of_Expr ex
 155  , ty ~ Type_Root_of_Expr ex
 156  , Eq_Type ty
 157  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 158                    (Error_of_Expr ast root)
 159  )
 160  => Proxy ex -> ast -> ty x -> ty y
 161  -> (x :~: y -> Either (Error_of_Expr ast root) ret)
 162  -> Either (Error_of_Expr ast root) ret
 163 check_eq_type ex ast x y k =
 164         case x `eq_type` y of
 165          Just Refl -> k Refl
 166          Nothing -> Left $ error_expr ex $
 167                 Error_Expr_Type_mismatch ast
 168                  (Exists_Type x)
 169                  (Exists_Type y)
 170 -- | Parsing utility to check that two 'Type_Type1' are equal,
 171 -- or raise 'Error_Expr_Type_mismatch'.
 172 check_eq_type1
 173  :: forall ast ex root ty h1 h2 a1 a2 ret.
 174  ( root ~ Root_of_Expr ex
 175  , ty ~ Type_Root_of_Expr ex
 176  , Eq_Type1 ty
 177  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 178                    (Error_of_Expr ast root)
 179  )
 180  => Proxy ex -> ast -> ty (h1 a1) -> ty (h2 a2)
 181  -> (h1 :~: h2 -> Either (Error_of_Expr ast root) ret)
 182  -> Either (Error_of_Expr ast root) ret
 183 check_eq_type1 ex ast h1 h2 k =
 184         case h1 `eq_type1` h2 of
 185          Just Refl -> k Refl
 186          Nothing -> Left $ error_expr ex $
 187                 Error_Expr_Type_mismatch ast
 188                  (Exists_Type h1)
 189                  (Exists_Type h2)
 190
 191 -- | Parsing utility to check that a type is has instance of a given 'Constraint',
 192 -- or raise 'Error_Expr_Constraint_missing'.
 193 check_constraint_type
 194  :: forall ast ex c root ty h ret.
 195  ( root ~ Root_of_Expr ex
 196  , ty ~ Type_Root_of_Expr ex
 197  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 198                    (Error_of_Expr ast root)
 199  , Constraint_Type c ty
 200  )
 201  => Proxy ex -> Proxy c -> ast -> ty h
 202  -> (Dict (c h) -> Either (Error_of_Expr ast root) ret)
 203  -> Either (Error_of_Expr ast root) ret
 204 check_constraint_type ex c ast ty k =
 205         case constraint_type c ty of
 206          Just Dict -> k Dict
 207          Nothing -> Left $ error_expr ex $
 208                 Error_Expr_Constraint_missing ast
 209                  {-(Exists_Dict c)-}
 210                  -- FIXME: not easy to report the constraint
 211                  -- and still support 'Eq' and 'Show' deriving.
 212                  (Exists_Type ty)
 213
 214 -- | Parsing utility to check that a type is has instance of a given 'Constraint'1,
 215 -- or raise 'Error_Expr_Constraint_missing'.
 216 check_constraint1_type
 217  :: forall ast ex c root ty h a ret.
 218  ( root ~ Root_of_Expr ex
 219  , ty ~ Type_Root_of_Expr ex
 220  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 221                    (Error_of_Expr ast root)
 222  , Constraint_Type1 c ty
 223  )
 224  => Proxy ex -> Proxy c -> ast -> ty (h a)
 225  -> (Dict (c h) -> Either (Error_of_Expr ast root) ret)
 226  -> Either (Error_of_Expr ast root) ret
 227 check_constraint1_type ex c ast ty k =
 228         case constraint_type1 c ty of
 229          Just Dict -> k Dict
 230          Nothing -> Left $ error_expr ex $
 231                 Error_Expr_Constraint_missing ast
 232                  (Exists_Type ty)
 233
 234 -- | Parsing utility to check that the given type is a 'Type_Type1'
 235 -- or raise 'Error_Expr_Type_mismatch'.
 236 check_type1
 237  :: forall ast ex root ty h ret.
 238  ( root ~ Root_of_Expr ex
 239  , ty ~ Type_Root_of_Expr ex
 240  , Unlift_Type1 (Type_of_Expr root)
 241  , String_from_Type ty
 242  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 243                    (Error_of_Expr ast root)
 244  )
 245  => Proxy ex -> ast -> ty h
 246  -> (forall (t1:: *).
 247      ( Type_Type1 t1 ty h
 248      , Lift_Type1 t1 (Type_Var0 :|: Type_Var1 :|: Type_of_Expr root)
 249      ) -> Either (Error_of_Expr ast root) ret)
 250  -> Either (Error_of_Expr ast root) ret
 251 check_type1 ex ast ty k =
 252         (`fromMaybe` unlift_type1 (unType_Root ty) (Just . k)) $
 253         Left $
 254                 error_expr ex $
 255                 Error_Expr_Type_mismatch ast
 256                  (Exists_Type (type_var1 SZero (type_var0 SZero)
 257                  :: Type_Root_of_Expr ex (Var1 Var0)))
 258                  (Exists_Type ty)
 259
 260 -- * Parsers
 261
 262 -- | Like 'expr_from' but for a root expression.
 263 root_expr_from
 264  :: forall lam ast root.
 265  ( Expr_from ast root
 266  , Root_of_Expr root ~ root )
 267  => Proxy root -> Proxy lam -> ast
 268  -> Either (Error_of_Expr ast root)
 269            (Exists_Type_and_Repr (Type_Root_of_Expr root)
 270                                  (Forall_Repr root))
 271 root_expr_from _ex _lam ast =
 272         expr_from (Proxy::Proxy root) ast
 273          Context_Empty $ \ty (Forall_Repr_with_Context repr) ->
 274                 Right $ Exists_Type_and_Repr ty $
 275                         Forall_Repr $ repr Context_Empty
 276
 277 -- | Parse a literal.
 278 lit_from
 279  :: forall ty lit ex ast hs ret.
 280  ( ty ~ Type_Root_of_Expr ex
 281  , Read lit
 282  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 283                    (Error_of_Expr ast (Root_of_Expr ex))
 284  ) => (forall repr. Sym_of_Expr ex repr => lit -> repr lit)
 285  -> ty lit -> Lambda_Var_Name
 286  -> Expr_From ast ex hs ret
 287 lit_from lit ty_lit toread ex ast _ctx k =
 288         case read_safe toread of
 289          Left err -> Left $ error_expr ex $ Error_Expr_Read err ast
 290          Right (i::lit) -> k ty_lit $ Forall_Repr_with_Context $ const $ lit i
 291
 292 -- | Parse a unary operator.
 293 op1_from
 294  :: forall root ty lit ex ast hs ret.
 295  ( ty ~ Type_Root_of_Expr ex
 296  , root ~ Root_of_Expr ex
 297  , Eq_Type (Type_Root_of_Expr root)
 298  , Expr_from ast root
 299  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 300                    (Error_of_Expr ast root)
 301  , Root_of_Expr root ~ root
 302  ) => (forall repr. Sym_of_Expr ex repr => repr lit -> repr lit)
 303  -> ty lit -> ast
 304  -> Expr_From ast ex hs ret
 305 op1_from op ty_lit ast_x ex ast ctx k =
 306         expr_from (Proxy::Proxy root) ast_x ctx $
 307          \ty_x (Forall_Repr_with_Context x) ->
 308         check_eq_type ex ast ty_lit ty_x $ \Refl ->
 309                 k ty_x $ Forall_Repr_with_Context (op . x)
 310
 311 -- | Parse a binary operator.
 312 op2_from
 313  :: forall root ty lit ex ast hs ret.
 314  ( ty ~ Type_Root_of_Expr ex
 315  , root ~ Root_of_Expr ex
 316  , Eq_Type (Type_Root_of_Expr root)
 317  , Expr_from ast root
 318  , Lift_Error_Expr (Error_Expr (Error_of_Type ast ty) ty ast)
 319                    (Error_of_Expr ast root)
 320  , Root_of_Expr root ~ root
 321  ) => (forall repr. Sym_of_Expr ex repr => repr lit -> repr lit -> repr lit)
 322  -> ty lit -> ast -> ast
 323  -> Expr_From ast ex hs ret
 324 op2_from op ty_lit ast_x ast_y ex ast ctx k =
 325         expr_from (Proxy::Proxy root) ast_x ctx $ \ty_x (Forall_Repr_with_Context x) ->
 326         expr_from (Proxy::Proxy root) ast_y ctx $ \ty_y (Forall_Repr_with_Context y) ->
 327         check_eq_type ex ast ty_lit ty_x $ \Refl ->
 328         check_eq_type ex ast ty_lit ty_y $ \Refl ->
 329                 k ty_x $ Forall_Repr_with_Context $
 330                  \c -> x c `op` y c
 331