Hi Daniel, cafe,
On 31/03/12 17:47, Daniel Gorín wrote:
Could you provide a short example of the code you'd like to write but gives you
problems? I'm not able to infer it from your workaround alone...
This problem originally came up on #haskell, where Rc43 had a problem
making a library with a common module that re-exports several other modules:
http://hpaste.org/66281
My personal interest is somewhat secondary, having not yet used hint in
a real project, but code I would like to write at some point in the
future is much like the 'failure' below, unrolled it looks like:
main = (print =<<) . runInterpreter $ do
setImports ["Prelude"]
interpret "1/5" (as :: Rational)
-- fails
Having to remember that Rational is defined as type Rational = Ratio
Integer and that Ratio is defined in Data.Ratio and then to add that to
the setImports list is a little inconvenient:
main = (print =<<) . runInterpreter $ do
setImports ["Prelude", "Data.Ratio" ]
interpret "1/5" (as :: Rational)
-- works
But for my own purposes this is probably much saner in the long run than
my newtype wrapping approach below.
However, this is not always possible: supposing Ratio itself was defined
as a type synonym of Ratio2, and Ratio2 was not exported. Perhaps this
is what Rc43 was experiencing, but I shouldn't speculate, as this is all
getting a bit theoretical - I should try out hint in the real world to
see if this problem makes things impractical for me - sorry for the noise!
Thanks,
Claude
Thanks,
Daniel
On Mar 31, 2012, at 6:19 PM, Claude Heiland-Allen wrote:
Hi all,
What's the recommended way to get hint[0] to play nice with type synonyms[1]?
A problem occurs with in scope type synonyms involving types not in scope.
I came up with this after looking at the source[2], but it makes me feel ill:
--8<--
-- hint and type synonyms don't play nice
module Main where
import Language.Haskell.Interpreter
import Data.Typeable as T
import Data.Typeable.Internal
import GHC.Fingerprint.Type
main = failure>> success
test t = (print =<<) . runInterpreter $ do
setImports [ "Prelude" ]
interpret "1/5" t
failure = test (as :: Rational)
-- Left (WontCompile [GhcError {errMsg = "Not in scope: type constructor or class
`Ratio'"}])
success = test (as :: Q)
-- Right (1 % 5)
newtype Q = Q Rational
instance Show Q where
show (Q a) = show a
showsPrec n (Q a) = showsPrec n a
instance Typeable Q where
typeOf _ = TypeRep (Fingerprint 0 0) (T.mkTyCon "Rational") []
--8<--
Thanks,
Claude
[0] http://hackage.haskell.org/package/hint
[1] http://www.haskell.org/onlinereport/decls.html#type-synonym-decls
[2]
http://hackage.haskell.org/packages/archive/hint/0.3.3.4/doc/html/src/Hint-Eval.html#interpret
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