Pattern Synonyms for Return and :>>=

[Icelandjack]

pattern RETURN :: a -> Program instr a
pattern RETURN x <- (view -> Return x)

pattern BIND :: instr a -> (a -> Program instr b) -> Program instr b
pattern BIND x k <- (view -> x :>>= k)

Bikeshed names.

[HeinrichApfelmus]

Looks intriguing!

Is it really necessary for the pattern synonym to be all caps?

Since which version of GHC are pattern synonyms supported? I would like to add a conditional to keep backwards compatibility with older compilers.

[Icelandjack]

The names I chose are tentative due to a chronic lack of imagination, conditional usage in lens

#if __GLASGOW_HASKELL__ >= 710
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ViewPatterns #-}
#endif

#if __GLASGOW_HASKELL__ >= 710
  -- * Pattern Synonyms
  , pattern Wrapped
  , pattern Unwrapped
#endif

(note pattern before the export)

#if __GLASGOW_HASKELL__ >= 710

pattern Wrapped a <- (view _Wrapped -> a) where
  Wrapped a = review _Wrapped a

pattern Unwrapped a <- (view _Unwrapped -> a) where
  Unwrapped a = review _Unwrapped a

#endif

[Icelandjack]

They may be made (explicitly) bidirectional like the Head pattern in the user guide

[HeinrichApfelmus]

Hm, I would very much like to name the patterns Return and Bind, of course. Unfortunately, these names are (essentially) already taken by the ProgramView type, so this would either have to break backward compatibility or introduce weird names for the patterns. I have to think about this.

[Icelandjack]

Returner and Binder?

[FranklinChen]

Any more thoughts about introducing pattern synonyms?

[turion]

It seems that pattern synonyms would only be useful for Program, not for ProgramT. I for my part only use ProgramT.