61 lines
2.2 KiB
Haskell
61 lines
2.2 KiB
Haskell
-- This module contains checks to be run *after* type inference has
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-- completed successfully. At that point we still need to do occurs
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-- checks and ensure that `main` has an acceptable type.
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module Type.ExtraChecks (extraChecks) where
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import Control.Applicative ((<$>),(<*>))
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import qualified Data.Map as Map
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import qualified Data.UnionFind.IO as UF
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import Type.Type ( Variable, structure, Term1(..) )
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import Type.State (Env)
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import Type.PrettyPrint ( pretty, ParensWhen(Never) )
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import Text.PrettyPrint as P
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extraChecks :: Env -> IO (Either [P.Doc] Env)
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extraChecks env =
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case mainCheck env of
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Left errs -> return $ Left errs
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Right env -> occursCheck env
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mainCheck :: Env -> Either [P.Doc] Env
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mainCheck env =
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case Map.lookup "main" env of
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Nothing -> Right env
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Just var
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| P.render (pretty Never var) `elem` ["Element","Signal Element"] -> Right env
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| otherwise ->
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Left [ P.vcat [ P.text "Type Error:"
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, P.text "'main' must be an Element or a (Signal Element)\n" ] ]
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occursCheck :: Env -> IO (Either [P.Doc] Env)
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occursCheck env = do
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errors <- concat <$> mapM isFinite (Map.toList env)
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return $ if null errors then Right env else Left errors
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isFinite :: (String, Variable) -> IO [P.Doc]
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isFinite (name, var) =
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do varIsFinite <- go [] var
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return $
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case varIsFinite of
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True -> []
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False -> [ P.vcat [ P.text "Type Error:"
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, P.text $ "Cannot construct infinite type for '" ++ name ++ "'\n"
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]
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]
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where
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go :: [Variable] -> Variable -> IO Bool
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go seen var =
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let check = go (var:seen) in
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case var `elem` seen of
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True -> return False
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False -> do
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desc <- UF.descriptor var
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case structure desc of
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Nothing -> return True
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Just struct ->
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case struct of
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App1 a b -> (&&) <$> check a <*> check b
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Fun1 a b -> (&&) <$> check a <*> check b
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Var1 a -> check a
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EmptyRecord1 -> return True
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Record1 fields ext -> and <$> mapM check (ext : concat (Map.elems fields))
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