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Grammar combinator for strings #8

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Grammar combinator for strings #8

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d2c9b2e
Grammar combinator for strings
edsko Feb 28, 2015
f17538f
Oops, sorry, remove redundant import
edsko Feb 28, 2015
48ceb8f
Nicer definition
edsko Mar 1, 2015
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20 changes: 17 additions & 3 deletions src/Language/JsonGrammar/Grammar.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,12 +20,12 @@ import Control.Category (Category(..))
import Data.Aeson (Value, FromJSON(..), ToJSON(..))
import Data.Aeson.Types (Parser)
import Data.Monoid (Monoid(..))
import Data.StackPrism (StackPrism, forward, backward, (:-)(..))
import Data.StackPrism (StackPrism, stackPrism, forward, backward, (:-)(..))
import Data.String (IsString(..))
import Data.Text (Text)
import Language.TypeScript (Type(..), PredefinedType(..))


import qualified Data.Aeson as Aeson
import qualified Data.Text as Text

-- Types

Expand Down Expand Up @@ -201,3 +201,17 @@ 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)

-- | Apply a prism to the top of the stack
--
-- TODO: It would be nicer if this was part of Data.StackPrism
top :: StackPrism a b -> StackPrism (a :- t) (b :- t)
top prism = stackPrism (\(a :- t) -> (forward prism a :- t))
(\(b :- t) -> (:- t) `fmap` backward prism b)

-- | Grammar for strings
--
-- (Defined explicitly rather than a Json instance so that we do not rely
-- on OverlappingInstances.)
string :: Grammar Val (Value :- t) (String :- t)
string = fromPrism (top (stackPrism Text.unpack (Just . Text.pack))) . grammar