32 lines
775 B
Haskell
32 lines
775 B
Haskell
module Check where
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import Expr ( Expr(..), betaEquiv, isSort, subst )
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import Data.List ((!?))
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import Control.Monad (guard)
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type Context = [Expr]
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findType :: Context -> Expr -> Maybe Expr
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findType g (Var k) = do
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t <- g !? fromInteger k
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kind <- findType g t
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guard $ isSort kind
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Just t
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findType _ Star = Just Square
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findType _ Square = Nothing
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findType g (App m n) = do
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Pi a b <- findType g m
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a' <- findType g n
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guard $ betaEquiv a a'
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Just $ subst 0 n b
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findType g (Abs t v) = do
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_argTypeValid <- findType g t
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bodyType <- findType (t : g) v
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_resTypeValid <- findType g (Pi t bodyType)
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Just $ Pi t bodyType
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findType g (Pi t v) = do
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argType <- findType g t
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guard $ isSort argType
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bodyType <- findType g v
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guard $ isSort bodyType
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Just bodyType
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