GHC Source Plugin for Data.String.Interpolate

Interpolate.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}

module Interpolate (plugin) where

import GhcPlugins
import HsSyn
import qualified Data.Generics as SYB

plugin :: Plugin
plugin = defaultPlugin
  { parsedResultAction = parsedPlugin
  }

parsedPlugin :: [CommandLineOption] -> ModSummary -> HsParsedModule -> Hsc HsParsedModule
parsedPlugin _ _ HsParsedModule{..} = do
  let hpm_module' = SYB.mkT transform `SYB.everywhere` hpm_module
  return $ HsParsedModule{ hpm_module = hpm_module', .. }

transform :: HsExpr GhcPs -> HsExpr GhcPs
transform (HsLit _ (HsString _ fs)) = HsSpliceE NoExt $ mkHsQuasiQuote (mkVarUnqual "i") noSrcSpan fs
transform expr = expr

Main.hs

{-# OPTIONS_GHC -fplugin=Interpolate #-}

module Main where

import Data.String.Interpolate

a :: Int
a = 42

s :: String
s = "#{a} * #{a} = #{a * a}"

main :: IO ()
main = putStrLn s -- 42 * 42 = 1764