RebindableSyntax on individual do blocks

Mark Roberts

22 Jun 2015 22 Jun '15

2:39 p.m.

I have a program that uses both monads and indexed monads, and I'd like to use do-notation for each in the same source file. Is there a way to rebind syntax for only the do blocks that make use of an indexed monad? Thanks, Mark

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Sumit Sahrawat, Maths & Computing, IIT (BHU)

22 Jun 22 Jun

2:56 p.m.

I don't know anything about indexed monads, but it seems that you can use the 'where' keyword to rebind (>>) and return for any block you want [1]. An example from [1]: addNumbers = do 80 60 10 where (>>) = (+) It might be possible to generate this where block using TH. There is also a quasi-quoter available for indexed-do-notation [2]. [1]: https://ocharles.org.uk/blog/guest-posts/2014-12-06-rebindable-syntax.html [2]: https://github.com/fumieval/indexed-do-notation On 23 June 2015 at 00:09, Mark Roberts wrote:

...

I have a program that uses both monads and indexed monads, and I'd like to use do-notation for each in the same source file. Is there a way to rebind syntax for only the do blocks that make use of an indexed monad?

Thanks, Mark

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-- Regards Sumit Sahrawat

Erik Hesselink

3:18 p.m.

Hi Mark, RebindableSyntax uses whatever (>>), (>>=) and return are in scope. So if you bind them in a `let` or `where`, you should be able to use different ones for different do blocks. Erik On Mon, Jun 22, 2015 at 8:39 PM, Mark Roberts wrote:

...

I have a program that uses both monads and indexed monads, and I'd like to use do-notation for each in the same source file. Is there a way to rebind syntax for only the do blocks that make use of an indexed monad?

Thanks, Mark

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Mark Roberts

3:19 p.m.

Ah, I missed that bit. Thank you! Mark On Mon, Jun 22, 2015 at 12:18 PM, Erik Hesselink wrote:

...

Hi Mark,

RebindableSyntax uses whatever (>>), (>>=) and return are in scope. So if you bind them in a `let` or `where`, you should be able to use different ones for different do blocks.

Erik

On Mon, Jun 22, 2015 at 8:39 PM, Mark Roberts wrote:

...
I have a program that uses both monads and indexed monads, and I'd like to use do-notation for each in the same source file. Is there a way to rebind syntax for only the do blocks that make use of an indexed monad?

Thanks, Mark

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Adam Bergmark

3:27 p.m.

Here's a pretty elegant (read: hacky?) way of working with RebindableSyntax: === Foo.hs module Foo where import Prelude hiding (Monad (..)) import qualified Prelude as P data MyMonad m a b = MyMonad { (>>=) :: m a -> (a -> m b) -> m b , (>>) :: m a -> m b -> m b , return :: a -> m a , fail :: String -> m a } ioMonad :: MyMonad IO a b ioMonad = MyMonad (P.>>=) (P.>>) P.return P.fail === Bar.hs {-# OPTIONS -fno-warn-name-shadowing #-} {-# LANGUAGE RecordWildCards #-} {-# LANGUAGE RebindableSyntax #-} module Bar where import Prelude import qualified Foo normalDo :: Monad m => m () normalDo = do return () -- Inferred: ioDo :: IO () ioDo = do return () where Foo.MyMonad{..} = Foo.ioMonad Cheers, Adam On Mon, Jun 22, 2015 at 9:19 PM, Mark Roberts wrote:

...

Ah, I missed that bit. Thank you! Mark

On Mon, Jun 22, 2015 at 12:18 PM, Erik Hesselink wrote:

...
Hi Mark,

RebindableSyntax uses whatever (>>), (>>=) and return are in scope. So if you bind them in a `let` or `where`, you should be able to use different ones for different do blocks.

Erik

On Mon, Jun 22, 2015 at 8:39 PM, Mark Roberts wrote:

...
I have a program that uses both monads and indexed monads, and I'd like to use do-notation for each in the same source file. Is there a way to rebind syntax for only the do blocks that make use of an indexed monad?

Thanks, Mark

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

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Adam Bergmark
Erik Hesselink
Mark Roberts
Sumit Sahrawat, Maths & Computing, IIT (BHU)