[Haskell-cafe] what are correct ways to translate haskell code ?

[Jeffrey Brown]

> Maybe it should somehow replace "osiudfhg" with "x1_of", but how is it
supposed to know that? It is a library function, after all.

My understanding was that the user would ask for a refactoring by
explaining the isomorphism between two data types.

I just remembered that Facebook open-sourced something called Retrie that
they use to refactor their own Haskell code. That should give a solid lower
bound on what is possible.

On Wed, May 24, 2023 at 8:02 AM MigMit <migmit at gmail.com> wrote:

> I don't think that's possible. Assume that there is a library that
> contains a module Stupid with a function osiudfhg, which is actually the
> same as fst:
>
> module Stupid where
>   osiudfhg :: (a, b) -> a
>   osiudfhg (a, _) = a
>
> If Alice uses that library, then her code could look like
>
> main = putStrLn "print some magic number" >> print ( osiudfhg v )
>
> How is Bob's code supposed to look? Maybe it should somehow replace
> "osiudfhg" with "x1_of", but how is it supposed to know that? It is a
> library function, after all.
>
> Yes, it might analyze source code of the Stupid module, but this is a
> daunting task.
>
> > On 24 May 2023, at 14:52, profited--- via Haskell-Cafe <
> haskell-cafe at haskell.org> wrote:
> >
> > let's consider this example
> >         Alice has 1.hs like this
> >                 v :: (,) Int Bool
> >                 v = (,) 0 False
> >
> >                 main :: IO ()
> >                 main = putStrLn "print some magic number" >> print ( fst
> v )
> >
> >         Bob download 1.hs from Alice
> >
> >         Bob would like to change 1.hs to 2.hs
> >         Bob want the programs [ 1.hs 2.hs ] to behave the same
> >
> >         the reason that Bob want to modify 1.hs may be
> >                 Bob does not like the type (,) in 1.hs
> >
> >         Bob has Vector_2.hs
> >                 module Vector_2 where
> >
> >                 data Vector_2 a b = C a b
> >
> >                 x1_of :: Vector_2 a b -> a
> >                 x1_of ( C x1 _ ) = x1
> >
> >                 x2_of :: Vector_2 a b -> b
> >                 x2_of ( C _ x2 ) = x2
> >
> >         Bob like his Vector_2.hs
> >         Bob thinks the Vector_2 shall be good enough to replace (,) in
> 1.hs
> >
> > i want to create a translator.hs for Bob
> >         Bob tell the translator.hs that Bob want to replace (,) with
> Vector_2 in 1.hs
> >         translator.hs automatically translate 1.hs to 2.hs
> >         2.hs shall look like this
> >                 import Vector_2
> >                         ( Vector_2 )
> >                 import qualified Vector_2
> >
> >                 v :: Vector_2 Int Bool
> >                 v = Vector_2.C 0 False
> >
> >                 main :: IO ()
> >                 main = putStrLn "print some magic number" >> print (
> Vector_2.x1_of v )
> >
> > what shall i do ?
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