Using GHC's parser and rendering the results is unreasonably difficult
After a couple hours, 30-some browser tabs, and attempting to use ghc-simple to paper over some annoyances with GHC's API (dynFlags/session-stuff, particularly), I gave up.
I then opened up haskell-src-exts and found the function I wanted in a minute or two.
import qualified Language.Haskell.Exts.Parser as P parsePls' :: String -> IO () parsePls' s = print $ P.parseExp s
This is where I got stuck:
Prelude> parsePls "1 + 1" Too late for parseStaticFlags: call it before runGhc or runGhcT
This is the code I was working with before I gave up on GHC:
module ParsePls where import DynFlags import FastString import qualified GHC import qualified GhcMonad as GM import HsSyn import Lexer import Outputable import Parser import RdrName import SrcLoc import StaticFlags import StringBuffer import qualified Language.Haskell.GHC.Simple as S import qualified Language.Haskell.GHC.Simple.Types as ST import System.Environment main :: IO () main = do [expr] <- getArgs parsePls expr parsePls :: String -> IO () parsePls s = do initStaticOpts let sbuf = stringToStringBuffer s srcloc = mkRealSrcLoc (mkFastString s) 1 1 (dynflags, _) <- S.getDynFlagsForConfig ST.defaultConfig -- dynflags <- undefined -- GHC.getSessionDynFlags -- unP :: P a -> PState -> ParseResult a -- mkPState :: DynFlags -> StringBuffer -> RealSrcLoc -> PState -- parseExpression :: P (LHsExpr RdrName) -- type LHsExpr id = Located (HsExpr id) -- Defined in ‘HsExpr’ let parseResult = unP parseExpression (mkPState dynflags sbuf srcloc) case parseResult of POk _ (L _ mdl) -> print $ showPpr dynflags mdl PFailed ss _ -> do putStrLn "Error occurred!" print ss
Whereas with haskell-src-exts I got:
Prelude> parsePls' "1 + 1" ParseOk (InfixApp (Lit (Int 1)) (QVarOp (UnQual (Symbol "+"))) (Lit (Int 1)))
Which was perfectly satisfactory.
Is there a reason it has to be this difficult?