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
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