Hello everyone, we are trying to use the GHC API for a source-to-source transformation on Haskell programs. The result of parsing and typechecking a module enables us to apply the transformation, but writing the transformed module back using the pretty printer (Outputable) generates invalid Haskell code. For one thing, since even the names defined in the current module are fully qualified, the resulting code is not valid anymore. This can be worked around, but there is another issue: Simply reading the following program and then writing it out using the pretty printer renders the resulting code invalid.
module Main where main = do if True then putStrLn "longlonglonglonglonglongline" else return () longlonglonglonglonglonglonglonglonglonglonglongname $ "test" longlonglonglonglonglonglonglonglonglonglonglongname = putStrLn
The result looks like this:
Main.main = do if GHC.Bool.True then System.IO.putStrLn "longlonglonglonglonglongline" else GHC.Base.return () Main.longlonglonglonglonglonglonglonglonglonglonglongname GHC.Base.$ "test" Main.longlonglonglonglonglonglonglonglonglonglonglongname = System.IO.putStrLn
There are two different problems in this output: 1) the indentation of "if ... then ... else" violates the "do"-block layout rule 2) the indentation of the long function call is invalid It looks like those problems could be avoided if the pretty printer could be configured to consistently use "do { ... ; ... }" notation, but we have been unable to figure out how. Is there a canonical way to use the GHC API to pretty print to valid Haskell code? Kind regards, Jan Appended is our current code to execute the transformation above (the module to be read is expected in a file "dummy.hs" for simplicity). Please excuse if this might not be a minimal example. module Main where import GHC import GHC.Paths import Outputable main = do x <- runGhc (Just libdir) $ do dflags <- getSessionDynFlags setSessionDynFlags (dflags { hscTarget = HscNothing, ghcLink = NoLink }) target <- guessTarget "dummy.hs" Nothing setTargets [target] load LoadAllTargets graph <- getModuleGraph let unparsedmod = head graph parsedmod <- parseModule unparsedmod typecheckedmod <- typecheckModule parsedmod let Just renamedsource = renamedSource typecheckedmod (group,_,_,_,_) = renamedsource moduledings = (ms_mod unparsedmod) return (showSDoc (ppr group)) putStr $ x ++ "\n" -- If you're happy and you know it, syntax error!