48 lines
1.3 KiB
Haskell
48 lines
1.3 KiB
Haskell
module Nix.Atoms where
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import Data.Data
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import Data.HashMap.Strict (HashMap)
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import Data.Text (Text, pack)
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import GHC.Generics
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-- | Atoms are values that evaluate to themselves. This means that
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-- they appear in both the parsed AST (in the form of literals) and
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-- the evaluated form.
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data NAtom
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-- | An integer. The c nix implementation currently only supports
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-- integers that fit in the range of 'Int64'.
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= NInt !Integer
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-- | Booleans.
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| NBool !Bool
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-- | Null values. There's only one of this variant.
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| NNull
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-- | URIs, which are just string literals, but do not need quotes.
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| NUri !Text
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deriving (Eq, Ord, Generic, Typeable, Data, Show)
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class ToAtom t where
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toAtom :: t -> NAtom
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instance ToAtom Bool where toAtom = NBool
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instance ToAtom Int where toAtom = NInt . fromIntegral
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instance ToAtom Integer where toAtom = NInt
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class FromAtom t where
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fromAtom :: NAtom -> t
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fromAtoms :: [NAtom] -> t
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fromAtomSet :: HashMap Text NAtom -> t
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-- | Convert a primitive into something which can be made from a
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-- constant. So for example `convert 1 :: Expression`
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convert :: (ToAtom prim, FromAtom t) => prim -> t
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convert = fromAtom . toAtom
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-- | Conversion to environment variables for constants.
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atomToEnvString :: NAtom -> Text
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atomToEnvString = \case
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NInt i -> pack $ show i
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NBool True -> "1"
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NBool False -> ""
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NNull -> ""
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NUri uri -> uri
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