This Haskell library provides quasiquote string interpolation with customizable concatenation for arbitrary types.
The default case uses Monoid and IsString:
import Exon (exon)
import Data.Text (toUpper)
newtype Name =
Name Text
deriving newtype (Show, Monoid, IsString)
instance Semigroup Name where
Name l <> Name r = Name (l <> " | " <> r)
lastName :: Name
lastName = "Fry"
up :: Name -> Name
up (Name name) = Name (toUpper name)
>>> [exon|Philip J. #{up lastName}|]
Name "Philip | J. | FRY"Individual segments are tokenized at whitespace boundaries, expressions between #{ and } are inserted verbatim.
The default implementation ignores whitespace when concatenating, while it is preserved for String, Text etc.
Customization
Concatenation is performed by the class Exon.Exon:
class Exon (tag :: Type) (a :: Type) where
convertSegment :: Segment a -> Result a
appendSegments :: Result a -> Segment a -> Result a
insertWhitespace :: Result a -> String -> Segment a -> Result a
concatSegments :: NonEmpty (Segment a) -> aAll methods have default implementations.
The tag parameter is an arbitrary type that allows the creation of different quoters, with exon using the tag
ExonDefault.
In order to get the default quoter to support custom rules for a type, one simply has to write an instance:
import Exon (Exon, ExonDefault, Result)
import qualified Exon as Segment (Segment(..))
instance Exon ExonDefault Name where
convertSegment = \case
Segment.String s -> Result (Name s)
Segment.Expression name -> Result name
Segment.Whitespace ws -> Result (Name " >>> ")Acknowledgments
Inspired by the magnificent string-interpolate.
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