30 lines
645 B
Haskell
30 lines
645 B
Haskell
module Database
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( Clause(..)
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, Database(..)
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, seekAndInstantiate, seek
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) where
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import Binding
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import Nondeterminism
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import Terms
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import Control.Monad
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import Control.Applicative
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data Clause = Clause Term [Term]
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data Database = Database
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{ clauses :: [PrologStream Clause]
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}
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seekAndInstantiate :: Term -> Database -> PrologStream Term
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seekAndInstantiate goal db = do
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seek goal db
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instantiate goal
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seek :: Term -> Database -> PrologStream ()
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seek goal db = do
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foldr (<|>) mzero (map doClause (clauses db))
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where
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doClause clause = do
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Clause chead body <- clause
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unify goal chead
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forM_ body $ \newGoal -> seek newGoal db |