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Combinator for defining a grammar by enumeration #9

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Combinator for defining a grammar by enumeration #9

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13 changes: 12 additions & 1 deletion src/Language/JsonGrammar/Grammar.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ import Data.StackPrism (StackPrism, forward, backward, (:-)(..))
import Data.String (IsString(..))
import Data.Text (Text)
import Language.TypeScript (Type(..), PredefinedType(..))

import qualified Data.Aeson as Aeson


-- Types
Expand Down Expand Up @@ -201,3 +201,14 @@ defaultValue x = Pure f g
-- | Create a 'pure' grammar from a 'StackPrism'.
fromPrism :: StackPrism a b -> Grammar c a b
fromPrism p = Pure (return . forward p) (backward p)

-- | Define a grammar by enumerating the possible values
--
-- For example:
--
-- > bool :: Grammar Val (Value :- t) (Bool :- t)
-- > bool = enumeration [(True, "true"), (False, "false")]
enumeration :: Eq a => [(a, Text)] -> Grammar Val (Value :- t) (a :- t)
enumeration = mconcat . map aux
where
aux (a, txt) = defaultValue a . literal (Aeson.String txt)