30 lines
1.0 KiB
Haskell
30 lines
1.0 KiB
Haskell
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{-# LANGUAGE TemplateHaskell #-}
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module NotCPP.Utils where
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import Control.Applicative ((<$>))
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import Language.Haskell.TH
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-- | Turns 'Nothing' into an expression representing 'Nothing', and
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-- @'Just' x@ into an expression representing 'Just' applied to the
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-- expression in @x@.
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liftMaybe :: Maybe Exp -> Exp
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liftMaybe = maybe (ConE 'Nothing) (AppE (ConE 'Just))
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-- | A useful variant of 'reify' that returns 'Nothing' instead of
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-- halting compilation when an error occurs (e.g. because the given
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-- name was not in scope).
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maybeReify :: Name -> Q (Maybe Info)
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maybeReify = recoverMaybe . reify
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-- | Turns a possibly-failing 'Q' action into one returning a 'Maybe'
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-- value.
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recoverMaybe :: Q a -> Q (Maybe a)
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recoverMaybe q = recover (return Nothing) (Just <$> q)
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-- | Returns @'Just' ('VarE' n)@ if the info relates to a value called
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-- @n@, or 'Nothing' if it relates to a different sort of thing.
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infoToExp :: Info -> Maybe Exp
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infoToExp (VarI n _ _ _) = Just (VarE n)
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infoToExp (DataConI n _ _ _) = Just (ConE n)
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infoToExp _ = Nothing
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