Opened 7 years ago

Last modified 23 months ago

#3205 new feature request

Generalized isomorphic deriving

Reported by: ajd Owned by:
Priority: normal Milestone:
Component: Compiler Version: 6.10.2
Keywords: language Cc:
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: None/Unknown Test Case:
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:


A newtype is isomorphic to the type that it is based on. For example, newtype A = A Int is isomorphic to Int, so it is possible to automatically derive all of Int's instance for A.

It would be nice if this could be extended to other datatypes that were isomorphic to each other. For example, this would work

data K a = K a a a

instance C (K a) where

data L a = L a a a
  deriving (Eq,C<-K,Show)

where the C<-K notation means "derive an instance of C for this type that is 'the same as' the instance of C for K". The compiler would have to check that K and L were actually isomorphic.

I don't know if this is possible with the current internals of GHC, but it would be cool if it would be done. My main usage scenario would be deriving things for single-argument data constructors based on tuples; for example for serialization classes.

Change History (2)

comment:1 Changed 7 years ago by igloo

  • difficulty set to Unknown
  • Milestone set to _|_

Thanks for the suggestion.

comment:2 Changed 23 months ago by thomie

  • Keywords language added
  • Type of failure set to None/Unknown
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