Chris, On 23/04/2008, at 12:41, C.M.Brown wrote:
Hello,
I want to use the ghc evaluator on the fly for some refactorings within HaRe. However, I notice that runstmt ::Session -> String -> IO RunResult.
Is there anyway I can grab the result of the evaluated expression as a String (rather than it being outputted to the terminal)?
The result of an expression is not a String, but an arbitrary value of some type. If there is a Show instance around for it, you can use that to get a String. One way to do that (untested):
nameToString :: Session -> Name -> IO String nameToString cms@(Session ref) name = do dflags <- GHC.getSessionDynFlags cms do let noop_log _ _ _ _ = return () expr = "show " ++ showSDoc (ppr name) GHC.setSessionDynFlags cms dflags{log_action=noop_log} mb_txt <- GHC.compileExpr cms expr case mb_txt of Just txt_ | txt <- unsafeCoerce# txt_, not (null txt) -> return $ Just txt _ -> return Nothing `finally` GHC.setSessionDynFlags cms dflags
The expression "show <name>" is evaluated via compileExpr. CompileExpr will return a HValue that you need to cast to a String. Or one can use dynCompileExpr instead. The code takes care of temporarily replacing log_action to capture the type error arising in the case there is not a Show instance available. A way to tell runStmt that you don't want the result outputted to stdout is to enable the flag -no-print-bind-result. It would be nice to wrap this code in a more friendly API. Hopefully the SoC project will take care of that ! Cheers pepe